What cyborg clams can teach us about the ocean

On August 23, 2023 By Dan KillamIn clams1 Comment

Every clam is a door into the sea. If the “door” of its shell is open, the clam may be happily breathing, or eating, or doing other weirder things. If the door is closed, it may be hiding from a predator, or preventing itself from drying out at low tide, or protecting itself from some other source of stress. It turns out that by monitoring the opening and closing of a clam’s shell valves, a field called valvometry, scientists can learn a lot about the clam’s physiology, its ecology and the environment around it.

Valvometry involves attaching waterproof sensors to each shell valve of the bivalve, to measure the distance between them and their movement. Researchers have used valvometers to figure out that bivalves can be disturbed by underwater pollution like oil spills, harmful algal blooms, and more unexpected sources such as noise and light pollution.

A great video from Tom Scott discussing a Polish program to monitor water quality with valvometry

Giant clams are a group of unusually large bivalves (some species reach up to 3 feet long!) native to coral reefs of the Indo-Pacific, from Australia to Israel. They grow to such large size with the help of symbiotic algae living in their flesh, the same kind that corals partner with the corals that build the reefs. The algae photosynthesize and share the sugars they make with their host clam, and the clam gives the algae nitrogen fertilizer and other nutrients, a safe home from predation and even helps channel light to the algae using reflective cells called iridophores.

A *Tridacna derasa* clam in the Biosphere ocean. It has deep green flesh, covered with yellow stripes of iridophores and a blue fringe at the edge.

Previous studies have used valvometers on giant clams, but I was always perplexed by how few studies there were: only two that I know of! One study on clams in New Caledonia figured out that the clams partially close every night and bask wide open during the day. The clams’ shell opening behavior and growth was found to become more erratic at temperatures above 27 °C, and when light levels become too great. Another study showed the clams start to clam up when exposed to UV light to protect themselves from a sort of sunburn, which is a real threat in the shallow reef waters they live in.

Two clams sitting next to each other in the B2 ocean. They often moved themselves to “snuggle” next to each other this way. Safety in numbers!

There is clearly a lot of information to pick up about how clams react to their environments, which can help us understand the health of the clams and also the corals around them. Coral reefs are under global stress from climate change, overfishing and pollution. Giant clams are some of the most prolific and widespread bivalve inhabitants of reefs, and represent an appealing potential biomonitor of reef conditions. Many giant clam species are threatened by the same stressors that influence the corals which build the reefs they live on, as well as overharvesting for food and their shells. For that reason, wild examples should clearly not be bothered by applying valvometric sensors. But giant clams are increasingly grown for the aquarium trade, resulting in a wealth of cultured specimens which could serve as sentinels of reef health, if they were fitted out with sensors. All of these motivators made me more and more curious of why we don’t have more literature monitoring the behavior of these clams with valve sensors.

I wondered if one of the limiting factors preventing the use of valvometry on giant clams is expense and ease of access. Giant clams live primarily in regions bordering developing countries in the Indo-Pacific, and almost all the professional aquaculture of clams for the reef trade happens in such countries, including places like Palau, Thailand, and New Caledonia. These countries are far removed from the places where most of the proprietary valvometric systems are manufactured. These systems can cost several thousand dollars even in Europe, never mind Palau, where arranging the import of electronics can be difficult.

When I started my postdoctoral fellowship at Biosphere 2 in 2020, I set out to grow two dozen smooth giant clams (Tridacna derasa, a species which can grow to about 2 feet long) in the controlled environment of the Biosphere 2 ocean, a 700,000 gallon (over 2.6 million liter) saltwater tank used to grow corals and tropical fish and kept at a stable year-round temperature of 25 °C. We suspended a series of LED lights intended to simulate the powerful light levels these clams experience in the wild (light is a lot brighter in the tropics than it is in Arizona!). The main focus of my project involved measuring the shell chemistry of the clams, to determine how their body chemistry changed as they grew from mostly getting their energy from filtering algae food from the water like other clams, to getting most of their energy from sunlight like a plant. But as a “side project” I set about measuring the behavior of the clams with custom-built valvometers based on open-source, inexpensive hardware that would be more accessible to researchers in the developing world. That work has since been published in PLoS One!

In our design, we used Hall effect sensors. Hall effect sensors generate a voltage when a change in magnetic field is detected. They are cheap, easily obtained for less than $1.50 apiece and are common in the electronics hobby trade. You might have encountered one in a home security system door/window sensor, where they help detect if a door is open or shut. We stuck a hall sensor soldered to a long copper cable to one valve of a clam, and a small magnet to the other valve. When the clam closed, we could measure exactly how closed it was. You can see why I started off by calling clams doors into the sea: we were literally measuring them that way!

Showing the sensor soldered to the three strands of the cable.

But here the first challenge of my project appeared. The off-the-shelf Hall sensors don’t come in waterproof form, and I learned quickly that the ocean really, really loves to break my gear. After dozens of failures, I settled on coating the sensors in waterproof grease, wrapping that in heat-shrink tubing and then sealing that inside of aquarium-grade silicone. During this process, a gifted technician at Biosphere 2 named Douglas Cline helped with iterating on the first prototypes. At a certain point I taught myself to solder so I could do my part to improve the sensors.

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A post shared by Biosphere 2 (@biosphere2)

It was also hard to figure out how to attach the sensors and magnets to the clams in a durable way. Neither of the prior studies mentioned how they attached the sensors to giant clams, and I tried and failed with literally a dozen different ways before settling on “pool putty,” a two-part adhesive often used to seal leaks in pools that can cure underwater. I found the pool putty had trouble attaching to the clams’ shells on its own, so I combined it with a special kind of cyanoacrylate superglue called “frag glue,” often used to attach pieces of corals to growth stubs. I also had to find a way to attach it to the clams without stressing them out. I determined five minutes out of the water was enough time to get the sensors attached to the clams, after which they could be returned to the water to finish curing. While giant clams are adapted to spend extended periods out of the water in their natural intertidal environment, we wanted to make sure to minimize their stress however possible, to ensure they would show natural cycles of behavior in the data.

Figure from the paper showing: A) schematic of the sensor attached to the clam, linked to an Arduino microcontroller and Raspberry pi computer. B) A sensor attached to one of the clams

We were pleased to see the cyborg clams seemed to pay no mind to the sensors. Giant clams are adapted to encourage all sorts of other critters to live on their shells as a form of natural camouflage, and I think the clams interpreted the sensors as pieces of coral or anemones sticking to the side of their shell. Whatever the case, as long as we kept the cable pointing to the side away from the clams’ flesh, they opened five minutes after being returned to the water, and their behavior and growth rates were indistinguishable from the clams that didn’t have sensors attached.

One of what became many sunsets on the Biosphere 2 ocean shore troubleshooting the clam sensors! Pardon the chaos: mad scientist at work!

So how did we measure the voltages coming from the sensors? Our design featured an Arduino microcontroller, sort of like a smart circuit board which can measure the voltages coming back over the copper cables. Arduinos are very cheap, and we chose a $25 model. Even more importantly, Arduino has a huge library of plug-ins available to keep the exact time of each observation using a clock attachment, and the data can be uploaded to SD cards or an attached computer. For the attached computer, I used a Raspberry Pi computer, which are open-source Linux-based tiny computers that are very cheap! Or rather they were very cheap before the pandemic, but fortunately there a lot of open-source alternatives that can be obtained more cheaply. We logged the data on the Raspberry Pi as it rolled over from the Arduino, and I could watch the read-out on a monitor right on the Biosphere 2 beach. We set the Arduino to record every 5 seconds.

Sensors attached to four of the clams. Notice the one on top left has closed a bit, after sensing my presence! They have eyes so they were able to detect me 😀

We ran the sensors for three months. During that time, the baby giant clams grew almost an inch! What did the sensors record them doing? During the day, the clams basked wide-open, exposing as much of their tissue as possible to light (other than the times that I disturbed them by swimming above them, of course)! This schedule of opening aligned pretty closely with the times that maximum sunlight hit their part of the Biosphere 2 ocean: the mornings, because the clams were on the east side of the building. At this time of day, the clams want to expose their symbiotic algae to as much light as possible, so they can conduct photosynthesis and make sugars that the clams use as food!

A) Plot of the valvometry data. Points higher on the plot mean the clam was more closed, up to 100% closed. The clams proceeded by opening in the early morning and then closing in the early afternoon. The big red circles represent times that the clams closed briefly, with bigger circles representing a longer time spent closed. Most of these rapid closures happened at night. B. A plot of Photosynthetically active Radiation (the amount of light the clams had to use for photosynthesis). The highest values were in the mid-morning when the clam lights were running in combination with direct sunlight hitting them from above.

Around mid-afternoon, the clams started to close partially, to about half closed. Why might that be? My hypothesis is that this posture represents a kind of “defensive crouch” to protect themselves from predators, in this case fireworms that live in the Biosphere 2 Ocean and were constantly kicking the clams’ tires. Similar nighttime behavior was observed in wild clams in a previous study, but not in a study that took place in a small predator-free terrarium tank. By remaining partially closed, the clams are prepared to rapidly close completely if they feel a predator approaching. But they only expend that energy of staying in that posture if predators are around!

One of the fireworms that proved to be my nemesis and continually attacked the clams during the experiment

And approach the fireworms did. We observed frequent closures at night lasting anywhere from a few seconds to hours, likely partially related to the activity of the worms around the clams. But the clams were engaging in another activity at night: filter feeding! Giant clams really get to have their cake and eat it too, because during the day, they act like a plant, but at night, they eat other plants in the form of plankton that they filter feed out of the water using their gills! At regular intervals, the clams need to clear uneaten material from their gills in a process sometimes called “valve-clapping”. The clams yank their shell valves together rapidly to force water out, blowing out pseudofeces: unwanted material packaged with mucus. We measured this valve-clapping mostly at night. The clams are likely scheduling this activity for the night-time so they can prioritize staying open and filter feeding during the day!

Figure comparing how often clams closed per day to measures of how high plankton numbers were in the Biosphere 2 ocean (chlorophyll is a marker of phytoplankton while phycocyanin is a measure of cyanobacteria), and how high the light levels were. Peaks in closure activity often happened shortly after rises in algae.

We observed that the frequency of valve clapping aligned closely with the rises and falls of chlorophyll concentration in the Biosphere 2 ocean, which is a measure of how much plankton is in the water column. The clams would engage in a burst of valve clapping around 4 days on average after a bloom in chlorophyll, suggesting they were filtering out plankton after they had died and settled to the bottom where the clams could eat them. We also found that the clam’s filtering activity peaked at times of highest pH. This likely is due to the fact that higher pH means the algae around the clams are being more active, and pulling CO2 in from the water to use in photosynthesis, making the water less acidic. More photosynthesis means potentially more material for the clams to filter through! This data helps quantify how giant clams help filter the water in their native environments! Coral reefs depend on very clear transparent water to allow maximum sunlight to reach the corals, and the filtering activity of giant clams likely plays a big role in helping preserve those conditions!

So we found that by adding sensors to clams, we could record their ability to feed from the sun, their feeding on plankton around them and their avoidance of predators. How can this technique be used next? We hope that by using cheap off-the-shelf resources and open-source software, we can enable more sensors to be put on clams all over the world, such as places where giant clams are farmed in Palau, New Caledonia, Thailand, Taiwan, Malaysia and more! If we can collect data on clam activity from all these places, we can compare how their feeding patterns differ in places that have more or less plankton floating by, or have more or less sunlight available, or different predators that affect the clams’ behavior. This data would have importance to the clams’ conservation, as well as our understanding of the reef overall. In future years, I hope we can develop a global network of cyborg giant clams from the Red Sea to the Great Barrier Reef, so we can better understand how these oversized and conspicuous but still mysterious bivalve work their magic!

An open letter to Stephen Colbert from a clam expert

On March 23, 2023March 24, 2023 By Dan KillamIn clamsLeave a comment

Abraclam Lincoln (photo source) next to a handful of *Mercenaria mercenaria*, a closely related kind of quahog (photo from Wikipedia), illustrating that Abraclam is indeed a chonker. To the right we have *Arctica islandica*, the famous long-lived clam, illustrating how hard it is to tell these clams apart without specialized training (photo from conchology.be).

Recently, a bit of an amusing clamfuffel arose when the Gulf Specimen Marine Lab, a research institute in Florida, began posting about a supposedly 214-year-old clam they named “Abraclam Lincoln”, in honor of potentially sharing a birth year with Honest Abe. The story went viral, and while some of their clammy claims turned out to hinge on flawed assumptions about how clams can be aged, it was still a worthwhile opportunity to communicate about the wonderful world of bivalves with people.

I was particularly impressed with how GSML went out of their way to correct the record as more info came in. Long story short, Abraclam is not the long-lived ocean quahog Arctica islandica (more on them below), but in fact a specimen of the southern quahog Mercenaria campechiensis, which lives along the Gulf coast and grows much more quickly than A. islandica. So the large clam they found was likely more like 40 years old, which is not too unusual for this species, rather than two centuries old. It also makes much more sense to find Mercenaria in Florida than Arctica. Additionally, external shell growth lines in Mercenaria are known to not be reliable for aging the species. The shell would have to be cut open to view internal lines to figure out how old Abraclam really is, which would require killing them. Fortunately, they released the clam rather than cut them in half for science.

Known range of *Arctica islandica* as a heatmap, compared to location of GSML on the Florida Panhandle. Source: OBIS

Slice through a *Mercenaria campechiensis* shell. The shell is lit from behind to show the annual growth lines. From Moss et al. 2021, written by fellow clam man David Moss, a friend of mine!

For what it’s worth, I still think Abraclam is an interesting specimen of M. campechiensis– they have a huge scar in their shell that would be interesting to learn more about (maybe they were hit by a dredge in their youth, healed the break and recovered to reach a ripe old age), and an unusual undulating margin at the edge of the shell that could be a deformity reported in the past literature for this species. Sometimes, scientists are wrong the first time, but we’re open about how we’re wrong, and everyone ends up learning more than we would have known otherwise.

So far so good. Then a bull had to wander into this delicate china shell with the entry of Stephen Colbert into the debate. I’ll let Stephen speak for himself, but needless to say, after his rant I feel a need to respond:

Before I dig into this clambake, Stephen, kudos to you for covering the whole story and not just the initial incorrect information. You addressed all the big inaccuracies, from the size not being tremendously out of the ordinary, to the incorrect species ID, to the incorrect age. Maybe it’s not so bad that people are getting their news from comedians rather than the news media these days! But while there were definitely some pearls of wisdom within your monologue, I have to point out some misconceptions here.

“The only thing more heartbreaking than the lies we were fed in this story…is growing up to be a clam expert!”
– Stephen Colbert

This is just plain false, since I’m not heartbroken, because clams are frickin’ awesome. Clams are way cooler than you or me, and that means by extension that the people who study them are pretty cool and interesting too (not really referring to myself. I’m just an eclamgelist along for the ride). So here are three facts about big old clams, and information about the clam experts who discovered these facts!

The ocean quahog lives to >500 years old!

*Arctica islandica* shell I saw on the beach in Massachusetts. This individual was likely several decades old when it died based on its fairly large size!

The ocean quahog Arctica islandica (which Abraclam was initially misidentified as) is tremendously long-lived, one of the longest-lived animals on earth! It has been confirmed to live to at least half a millenium! One individual caught off the coast of Iceland was aged to ~507 years by counting tiny growth lines in its shell via microscope, combined with radiocarbon dating. This clam was named Hafrún (meaning “ocean mystery” in Icelandic), but is sometimes called Ming due to it being born in the Ming dynasty of China. So put that in your Ming vase and smoke it Colbert!

https://museum.wales/media/48824/Ming-blog1image1.jpg — Part of the shell of Hafrún, which was cut open to determine its age via internal growth lines. Source: Museum Wales

Several scientists worked on aging Ming, but Alan Wanamaker at Iowa State was a lead author on the original work. He uses growth lines in the shells of many clam species as records of climate change and is generally one of the nicest people you could have the opportunity to meet.

Tridacna gigas grows to over 4 feet long and hundreds of pounds!

Large specimens of giant clams that are around 3 feet long at the California Academy of Science collection.

The author sitting in a scale model of *Tridacna gigas* at the Monterey Bay Aquarium

Abraclam might be only 6 inches long (which is respectable as he/she is quite girthy; length isn’t everything, Stephen!), but there are other types of clams that are bigger than one Colbert in mass. The giant clam Tridacna gigas grows to over 4 feet long and weighs hundreds of pounds. They live on tropical coral reefs and use the power of the photosynthetic algae in their flesh to speed up their growth. So basically these clams are bigger and way more interesting than you, Stephen, since they get to go out and tan in the sun for lunch while you have to gobble down a slice of pizza.

Mei-Lin Neo at University of Singapore is considered the world’s leading expert on Tridacna, and has done more than almost anyone I know to describe all twelve currently known species of giant clams found around the world. She’s a tremendous advocate for giant clam conservation and gave an outstanding TED talk about them to boot. You should have her on your show to be honest.

Geoducks: they looked like that first!

WDFW employee holds large geoduck — A 6.5 pound geoduck and admiring Washington Department of Fish and Wildlife Volunteer (Source)

Speaking of girthy, long clams, I’d be remiss not to mention the geoduck, Panopea generosa. Pronounced “gooey-duck,” these clams looked like this long before any part of human anatomy existed, having been around in various forms since at least the Jurassic. They have a long siphon that they use like a snorkel when they dig deep in the mud, and they can live for almost 200 years.

Brian Black at the University of Arizona is an expert in using their shells as a record of climate change. He was part of a group that was able to stitch together the growth line records from multiple geoduck shells to make a continuous record of climate change going back to 1725. Seems appropriate to note that 1725 was the year that Casanova was born…a man who may have channeled some qualities of geoducks.

Local experts on Abraclam

I’d like to mention two of the experts who corrected the record about Abraclam Lincoln and provoked Stephen’s attack in the first place. Dr. Dan Marelli wrote an op-ed correcting the record on how Mercenaria clams are aged for the Tallahassee Democrat. He’s an expert scientific diver and has published papers on clams ranging from endangered scallops to invasive mussels. Scientific diving is crucial to understand clams in their native environment, and to assist in their conservation. If I had to choose who had more interesting stories at the bar, it’d be an easy decision to listen to the swashbuckling diver over the late-night TV host!

Dr. Edward Petuch at Florida Atlantic University reached out to GSML to make sure they knew the correct species ID for Abraclam. He is well-known for his work describing the change in ecology of mollusks in Florida and the Caribbean over the last several million years. GSML expressed interest in working with Dr. Petuch in the future, and I can confirm that I’ve had fruitful scientific collaborations start when other scientists have reached out to me about how I was totally, embarrassingly wrong. Being wrong in science is part of the job, and that’s why I’m glad this Abraclam story came out in the first place.

“So what does your son do? He’s a marine biologist. Does he work with dolphins? …I’m gonna say yes.”
-Stephen Colbert

To close out, I’d like to address Stephen’s assertion that my mom isn’t proud of me for being a clam expert. Stephen, I’ll have you know that my mom is the most enthusiastic patron of my clam science. She reached out to the local paper to anonymously tip them to interview me about my clam work, had me give a speech about clams at the local women’s group she’s a part of, and when I defended my PhD thesis, she made t-shirts to commemorate the occasion. I can confidently say I wouldn’t be Dan the Clam Man if it weren’t for her support. Thanks Mom!

My whole family mobbed my defense with t-shirts and it made my year pic.twitter.com/msJ3tJBNYJ
— Dan Killam (@DantheClamMan) April 7, 2022

Why I like scicomm on Mastodon!

On December 2, 2022 By Dan KillamIn scicomm1 Comment

A geoduck clam (also called "elephant clams") next to the elephant-like Mastodon mascot. The clam has along trunk-like siphon. — A geoduck clam (also called “elephant clams”) next to the elephant-like Mastodon mascot

Over the last couple weeks, I’ve seen hundreds of academics, nerds and everyday people I know open new accounts on Mastodon, in a phenomenon that has been called the great #TwitterMigration. Mastodon is an open-source microblogging platform similar in format to Twitter, but running on thousands of servers interconnected with each other in an open network called the “Fediverse” (referring to the fact that these services are “federated” to each other). Many researchers are disillusioned with the current state of Twitter, which was purchased recently by an erratic, bigoted oligarch, and are registering their disapproval by seeking out other places to share their science.

Personally, I am not “migrating” per se, as I have been using Mastodon for over 4 years now. I don’t intend to close my Twitter account, because I think the site will survive the current damage being done to it, though I’ve stopped posting for the time being, while they work through the process of learning the hard way that hate speech can never be allowed on the platform. I wanted to write about my experience using Mastodon to communicate science and why I think it has a lot of advantages over Twitter for certain use cases, precisely through the ways it does not seek to be a direct Twitter replacement.

Posting how I want

First of all, Mastodon gives me way more freedom to post the way I want. It is a true “micro-blog” in the way Twitter can’t be, since I get enough characters (500 at scicomm.xyz, and more on some servers!) to allow me to post a real paragraph. I have never found Twitter’s 180 characters to be enough space to really tell a satisfying story. Some people get around this by posting threads, but I also have never enjoyed writing threads! Other than that time I went on a giant clam fact rant. Mastodon also supports threads if you’re into that, and also allows you to set the visibility on your subsequent posts, so that your replies to yourself don’t spam everyone’s feed.

In my four years writing #clamfacts on Mastodon, I’ve written short facts. Long facts. Silly facts. Meaningful facts. I just have a lot more freedom with the format. Mastodon was also much faster to enable accessibility features like image descriptions than Twitter was. So the facts I shared are more accessible to disabled folks. While Twitter now includes alt-text, it still feels like Mastodon’s alt-text is a more mature feature. As with subtitles and other accessibility solutions, these features end up improving usability for everyone. In the case of alt-text, it gives me tons of space to describe scientific diagrams for anyone who might need additional context.

Mastodon recently added the ability to edit posts, which has been very advantageous for me, as a typo-prone individual. For Twitter, that feature is still locked behind a subscription. But even before editing was available on Mastodon, there was an option to “Delete and redraft”, which I used frequently to re-post when I had forgotten an image description, or to fix a typo. Mastodon has long provided far more options to control who can see a post and how, which is why I felt more incentive to be creative there than on Twitter.

A small pond by design: Engagement and sustained connection over reach

Twitter sometimes feels like an RSS feed with comments. Particularly for the more popular accounts or viral posts, while you can reply, there is such a torrent of feedback on the other end that it is difficult for them to respond to everyone. For my niche specialized clamposting, I am not interested in going viral. I just want to engage with people and learn from them as much as I share knowledge with them.

Mastodon is very well designed for this. Your posts get shared across the federated network, but only as much as other people “boost” it (analogous to retweeting) or reply to it. There are favorites (similar to the like button), but those are mostly just a direct message that someone liked a post, and have no impact on whether it spreads larger over the network. So the main people seeing my posts are my direct followers. And because Mastodon is a reverse chronological feed, with no opaque algorithm determining whether or not to show someone something, I am more confident that a bot moderator isn’t going to misidentify my clam content as NSFW and hide it by default from people’s feeds.

Culturally, Mastodon is driven by following people, and making your feed for yourself, rather than having posts from people you don’t follow pushed to you by a computer. If you follow someone back, you’re more likely to make a lasting connection through time, rather than trusting some algorithm to figure out who you enjoy to see. This leads to more lasting, meaningful connections in my experience. Truly powerful scicomm never happens in one direction; it relies on exchange.

I think that Mastodon will stay like this in the future, even as it continues to grow by leaps and bounds. Rather than one giant, sometimes dangerous ocean like Twitter, it’s more of a collection of small ponds. My reach is restricted to my followers and their followers, and sometimes their followers’ followers. That produces much more meaningful, sustained connections.

Hosted and moderated by scientists, for scientists

My home since the start has been Scicomm.xyz, a server run by a scientist in the UK going by the username Quokka. Recently he recruited another scientist and me to be moderators on the server, and we’re looking to add more. But since the start even before I was moderating myself, I’ve felt more secure sharing science when it’s hosted and moderated by another scientist. Even before Twitter laid off moderation staff en masse, and before the site announced scientific misinformation is now fair game, Twitter was not a place run by scientists, for scientists. If someone replied to me with misinformation about the coronavirus or climate change, my recourse against them was limited, since the moderation staff there are not exactly experienced peer reviewers. On Mastodon, there have always been data-conscious nerds running things. And now, there are a constellation of science–specific servers to choose from!

Science, including scicomm, is always more at home in an open-source environment

The last point I’ll bring up is that science always works better in an open-source environment. Mastodon is available free and open-source on Github for anyone to download, alter and run themselves. I prefer to use such open-source solutions in my own scientific work, from including Rstudio, QGIS, ImageJ, Raspberry Pi, Arduino, Ubuntu, Inkscape, Firefox/Thunderbird and more. So hosting my science communication on an open platform feels like preaching what I practice, as opposed to allowing a for-profit company to own my scientific content.

For all the reasons above, I have been extremely pleased to see the wave of scientists, technologists and other interested people join Mastodon over the last few weeks. I feel Twitter will still have a place in my science communication once it has worked through its current drama. But in the meantime, I look forward to sharing my clam facts with all the people I can, in my little pond on Mastodon.

A coral, a worm and some clams walk into a bar…

On May 31, 2022March 21, 2023 By Dan KillamIn Biology, clams1 Comment

The tree of life is often portrayed as a neatly branching structure, with each division point cleanly delineated and separated from its neighbors. The truth is that the various twigs of the tree of life often overlap and become tangled in a process we call symbiosis. I’ve talked about symbiosis before on this blog, which falls along a spectrum of wholesomeness. At one end we have mutualism, a partnership where both organisms benefit and achieve more than the sum of their parts. The other extreme is parasitism, when one organism benefits at the expense of the other. Between the two, there is a broad gray area including commensalism, when one organism’s presence doesn’t necessarily cost or benefit the other in any way. The tree of life is crowded and unpruned, and so sometimes the twigs might wrap around each other quietly and without much fuss. We live on a small planet, and have had to get used to living in uncomfortable intimacy with all sorts of creatures, such as the mites that are living on your eyelashes right now.

But things start to get really weird and tangled when the tree of life loops over on itself twice, or three times, or more. “Three-way” symbioses are surprisingly common, and the more you look for them, the more you realize that the tree of life is more of a knot than anything else.

A view of the *Heteropsammia* coral from the side

A recent paper from researchers in Bremen (Germany) and Saudi Arabia looked at such a three-way symbiosis between a coral, a worm and bivalves found off of Tanzania in East Africa. The relationship between solitary corals (Heteropsammia cochlea and Heterocyathus aequicostatus), a sipunculan worm (Aspidosiphon muelleri muelleri) and the clam Jousseaumiella, is a complex triangle of dependencies that had previously been noticed by other researchers, but never investigated at great depth. The worm lives with multiple tiny clams attached, all inside of a small solitary coral the size of a dime (1 cm long). Is the coral a willing host for this crowded boarding house, or has it been parasitized? Does the worm gain anything from the clams? The researchers sought to find out.

Part of the reason I enjoyed reading this study so much was that it had to take a narrative structure to describe the evolutionary ménage à trois of its focus. So much of modern science has moved away from anecdote to hard data, and while there is plenty of that to find in the study, it turns out that a lot of the study of symbiosis is storytelling. We need to know the setting and the characters.

In this case, the main characters are small solitary corals living in the tropical reefs of the Indo-Pacific. We denote them as solitary to distinguish them from their giant colony-forming compatriots that construct the coral reefs currently threatened by climate change and pollution. But like those giant reef-builders, these solitary corals get much of their food from sunlight through a mutualistic partnership with algae called Symbiodinium. The algae provide the host with sugars and other photosynthetic products, and the hosts give them nutrients and a safe cozy home in their tissue.

You might be thinking, “Wait! Dan just said this was a three-way partnership between a coral, a worm and some clams. So this is actually a four-way partnership between corals, worms, clams and algae?” You’d be exactly right. And I’m happy to say that the plot of this sordid story is about to thicken even further.

The side of the coral. See the little pores?

The Aspidosiphon worm is found in a spiral-shaped burrow inside of the skeleton of the coral. It is a pretty cozy home, with walls made of calcium carbonate by the coral, with breathing holes in the sides to allow the worm to breathe and release waste. The researchers wanted to know more about the structure of the burrow. Was it dug out by the worm using acid or an abrasive motion, like some clams use to dig into coral? So the researchers essentially gave the coral a CT scan to see its 3D internal structure. Inside they found growth features suggesting the coral grew around the worm, as if intentionally providing it a home.

Cross-sectional CT scans of the coral skeleton. In figure D, you can see the silhouette of the chambers of the snail shell where the worm made its first home!

Even more crazily, they found evidence that the worm had first settled inside an empty snail shell, like a hermit crab! The coral probably settled on a snail shell as a larva, and grew to engulf the whole snail shell, leaving growing space for the worm inside, with windows and all! So to review, this is now a five-way symbiosis between a dead snail, a worm that moved into its empty shell, the coral (powered by algae) that grew around it and encased the snail shell within its skeleton, and we haven’t even gotten to the clams. How many creatures are hiding stacked in this trench coat? Please bear with me as I explain!

An SEM image of Jousseaumiella. These are less than 1 mm long! Pinhead sized!

What are the clams doing in this picture? Jousseaumiella is part of a family of clams called Galeommatidae, which we previously mentioned on this blog in the context of some bivalves found growing in the gills of unfortunate sand crabs. Many members of the Galeommatidae family are parasitic or commensal with other marine organisms. In this case, Jousseaumiella are tiny flat-bodied clams less than 1 mm long, found attached to the body of the worm, squeezed inside the burrow in the coral’s skeleton. It feeds on the worm’s waste and potentially food particles coming through the pores in the sides of the burrow. Not the most dignified existence, but a more mobile home means more opportunities to eat a varied diet similar to that that the worm and coral are seeking out, and the clam also gets protection from predation tucked inside the coral. It is unclear if it benefits the worm directly to have clams attached to it.

A time lapse of the coral+worm moving from the paper’s supplement! It would be handy to navigate to greener pastures, if it became too muddy in a certain place!

It is, however, clear how living inside a coral would be a pretty good deal for the worm, which gets a stable, protective suit of carbonate armor to protect it from predators, and grows to fit it as it gets larger. They are normally found inside of rocks, shells and other hard inanimate objects, but having a living home is a cool upgrade. What is the coral getting out of the deal? The researchers note that the corals are often found in the crevices between other large reef-building corals, in areas of the reef that receive high supplies of nutrients and turbidity (dirt that blocks out light). These sorts of environments aren’t necessarily friendly places for a coral to be, since they reduce the light and therefore the food that the coral can receive from photosynthesis. These crevices also have a lot of variability in other conditions like temperature and water flow. But because the coral has hitched a ride on the back of a worm, it can actually move in the sediment to react to changing conditions and avoid being buried by piles of sediment floating by! The worm can also act as a sort of anchor preventing the worm from sinking in the sediment underneath, which would be a big hazard for the small, stubby coral on its own. The coral seems to go to great pains to make its partner comfortable, not growing its skeleton to cover the pore windows to the outside. The researchers note that as coral reefs worldwide are subject to increasing human-made pollution and climate change, it would be interesting to research whether this complex three-(five?) way symbiosis provides the various participants with an advantage compared to other corals.

So like any good story, this symbiosis features complex, growing characters, a dynamic setting, and still plenty of mystery demanding a sequel! To that end, there are lots of other great three-way symbioses to investigate. Snails which farm fungus that parasitizes plants. Bryozoans living on snail shells that have a hermit crab inside. Gobies serving as lookouts at the entrances of burrows built by shrimp, with a crab freeloader along for good measure. Algae and bacteria teaming up to attack mussels. The list keeps going! I could see this becoming quite a franchise!

New job! Where I’m going and how I got here

On January 18, 2022March 25, 2022 By Dan KillamIn academia, BiologyLeave a comment

Richmond, California’s Finances Remain Shaky — Richmond, CA from the air, showing the turbid waters of the SF Bay

Well folks, it finally happened. I found a permanent scientific job. On January 31st, I’ll be starting as an Environmental Scientist at the San Francisco Estuary Institute (SFEI), working on the Nutrient Management Strategy (NMS) program. NMS is a group trying to understand how nutrient supply in the San Francisco Bay works.

The SF Bay is an extremely nutrient-enriched environment (eutrophic) due to human pollution and natural factors, to the extent that if all other factors were equal, scientists would expect it to be a nasty green sludgy mess. Yet up to today, due to factors that are still debated, the SF Bay is in much better shape than it should be. It is not a dead zone, choked off by algal blooms and oxygen-starved in the way that other high-productivity regions such as parts of the Gulf of Mexico have become. Those factors may include the cloudiness (turbidity) of the Bay’s water limiting algae growth, naturally rapid tidal mixing with ocean water, and the influence of clams and other grazing animals keeping the populations of potentially harmful plankton suppressed.

However, there is also evidence that this resilience may be fading as water temperatures in the Bay increase and the ecology of the system changes with climate change. Oxygen levels are dropping and levels of harmful algae are rising, which endangers the health and livelihoods of millions of people in the SF Bay area who depend on a clean, ecologically functioning SF Bay. In my role at NMS, I will be assisting in processing and interpreting huge quantities of environmental data on temperature, dissolved oxygen, water flow, light levels, algae concentrations, and harmful algae toxins, to help figure out how the SF Bay works and how we can protect it. I will be assisting another scientist joining the team in deploying more sensors to monitor the Bay on a minute by minute basis, and also packaging the data to help create models which allow us to figure out the various moving parts that make it work.

In a way, this is oddly similar to the work I’ve done during my postdoc at Biosphere 2, where I’ve been growing giant clams in their 700,000 gallon ocean tank since May 2020. The clams are biological sensors have been recording the environment of the Biosphere 2 ocean through their shells and valve opening/closing activity, and I have had to decode their diaries through comparison with the environmental data we collect on light, pH, dissolved oxygen, chlorophyll and other measurements. The SF Bay is a site of enormously influential research which has been important to understand estuaries around the world, but it is still a mysterious body of water in many ways. NMS is trying to understand how all its complex pieces fit together, much like I’ve been doing at Biosphere 2, which is why I jumped at the opportunity to apply for the job.

I also am excited to get involved in this work because it’s immensely important for everyday people’s lives. The SF Bay provides millions of people with food, employment, recreation and overall well-being, and the science that NMS produces has real-world value for making policy and a concrete plan to keep the Bay healthy. It represents exactly the kind of science that I wanted to do since I first jumped into environmental biology as a 19-year-old at USC. At that time, I was interning at JPL studying historical trends in California rainfall data, so this new job represents a homecoming of sorts to California water science!

This job will be a bit of a change of pace from my present work as at first, because I’ll be part of a scientific team with a shared mission, unlike most of my prior research, where I came up with ideas, pitched them to my advisors and funders and then coordinated the projects to collect and analyze data. There will be more teamwork, and while academic publications will still be one of our products, we also will be writing reports for policymakers and stakeholders who are deciding on how to regulate nutrient levels in the Bay.

I also won’t be working with clams on an everyday basis! But as I mentioned before, clams do play a major role in the Bay in terms of filtering the water, and so it is likely we will need to understand the activities of the clams and other grazers to explain the trends in nutrients that we see. I didn’t start as a Clam Man, but my curiosity about clams meant that my attention kept being drawn to these enigmatic but influential creatures, and I expect that dynamic will continue. I am, and always will be, Dan the Clam Man.

I will continue to get my present clam projects out the door as publications, so there will be lots of clamsplaining in the future months as those get out the door. Regarding the Biosphere 2 clams, we still have four individuals of Tridacna derasa (the smooth giant clam) growing in the 700,000 gallon ocean tank, and intend to leave them as long-term research subjects and an exhibit for visitors to enjoy and learn about. We also have proposals in the work for new projects to expand on this work. I hope I can continue to visit in the coming decades and see our clams grow to be true giants, two feet in length! I also hope to acquire pet giant clams of my own, with names rather than specimen numbers, to be my friends rather than my research subjects.

I’ll be starting the new job remotely at the end of this month, to give myself time to tie off loose ends in Tucson, intending to move to the Bay Area by March. I will really miss Biosphere 2 and Tucson, but this isn’t the last they’ll see of me, because my collaborations with people here will continue into the future. I knew from the start as a postdoctoral researcher that my position would not be permanent, but it is still bittersweet to leave. I will miss hiking in the Sonoran desert, swimming in the Biosphere 2 ocean tank and also my advisor Diane Thompson and her lab here, full of people who have been a joy to work with.

But I am excited for this new chapter, because the postdoc life has been lately losing its luster for me. I’ve enjoyed being a postdoc for the freedom it entails, both in my research topics and the way I structure that work. But postdoc work is emotionally exhausting, as I have been a journeying academic contractor on “soft money”. My employment for the following year has always been contingent on the next grant coming through. Moving between different institutions on different continents has been a big weight on my family and my partner, who I miss greatly.

As a postdoc, while I’ve had fun and wouldn’t change anything about it, I have felt like a plane trying to take off in unfavorable weather. I could see the end of the runway approaching as my current funding ends in May, which was a scary feeling. I’m willing to hustle and fight for research funding, but not my basic income. Looking back, I have applied to around 45-50 academic positions (including postdocs) since finishing my PhD and got interviewed for less than ten percent of those, and received offers for two postdocs. When I got the offer from SFEI, which was itself a rigorous, multi-stage process over months, I cannot describe what a relief it was to clear out my “job applications” folder in my to-do list. This SFEI job will allow me to pursue marine science that helps the environment and people, in a more emotionally sustainable way.

I’m excited to start my next chapter and share with you all the discoveries our team makes about the SF Bay, while also continuing to clamsplain here on my own time. Keep an eye out for my Biosphere 2 studies, which will be rolling out over the next months as the data arrives!

Research Explainer: How I learned to stop worrying and trust the clams

On September 3, 2021 By Dan KillamIn clams, scicomm4 Comments

Two giant clams off the coast of Israel. Left: *Tridacna maxima*, the small giant clam. Right: *Tridacna squamosina*

Another year, another new paper is out, another clamsplainer to write! The fourth chapter from my PhD thesis was just published in Proceedings of the Royal Society B. This study represents five years of work, so it feels great to finally have it leave the nest. In this study, we investigated the comparative growth of fossil and modern giant clams in the Gulf of Aqaba, Northern Red Sea. Back in 2016 during my PhD, I knew I wanted to study giant clams because they are unique “hypercalcifying” bivalves that grow to huge sizes with the help of symbiotic algae living in their bodies. The clams are essentially solar-powered, and use the same type of algae that reef-building corals depend on! Unlike corals, which are the subject of a ton of research related to how they are threatened by climate change, habitat destruction and pollution, comparatively little is known of how giant clams will fare in the face of these environmental changes. Are they more resistant than corals, or more vulnerable?

T. squamosa on the reef off the coast of Eilat.

I had strong reason to suspect that the clams are struggling in the face of human changes to the environment. They can bleach like corals do when exposed to warm water, and have been observed to be harmed when waters are less clear since they are so reliant on bright sunlight to make their food. But I need a way to prove whether that was the case for the Red Sea. I needed to travel to a place where fossil and modern giant clams could be found side by side, so their growth could be compared using sclerochronology. We would count growth lines in their shells to figure out how fast the grandaddy clams grew before humans were around, and compare that ancient baseline to the growth rate of the clams in the present. Giant clams make growth lines every day in their shells, giving us the page numbers in their diary so we can figure out exactly how fast they grew! We can also measure the chemistry of their shells to figure out the temperatures they experienced from the oxygen isotopes, and even what they were eating from the nitrogen isotopes.

A map of the Gulf of Aqaba, where our study took place. My talented marine scientist partner Dana Shultz made this map!

It just so happened that UCSC’s Dr. Adina Paytan was leading an NSF-funded expedition to the Red Sea in summer 2016, which represented a perfect place to do this work. There are many age dated fossil reefs uplifted onto land around the Gulf of Aqaba on the coasts of Israel and Jordan, and there are three species of giant clam living in the Red Sea today: Tridacna maxima (the small giant clam), Tridacna squamosa (the fluted giant clam), and Tridacna squamosina. Tridacna squamosina is particularly special because it is only found in the Red Sea, making it an endemic species. It is extremely rare in the modern day, with likely only dozens of individuals left, making it potentially endangered.

So I set off with Adina and two other students to live for two months in in the blazing hot desert resort town of Eilat, Israel, working at the famous Interuniversity Institute. Getting a permit from the Israeli National Parks Authority, I collected dozens of empty giant clam shells (no clams were harmed in the course of this study!) from the surf zone and from ancient reefs ranging from a few thousand years to almost 180,000 years old. I also spent a week over the border in Aqaba, Jordan where I worked with Dr. Tariq Al-Najjar, my coauthor and director of the University of Jordan Marine Science Station. Tariq is a specialist in algal productivity in the Gulf and was an excellent resource in trying to understand how water quality has changed in the area through time. He pointed out that over the years, the Gulf of Aqaba has had an increased nutrient supply far above what it received in historic times. For nearly 20 years the Gulf was subjected to excess nutrients from Israeli fish farms, which caused tremendous damage to the reefs of the area with their releases of fish waste. The farms were finally forced to close after a long lobbying campaign from Israeli and Jordanian scientists and environmentalists. But even after the farm pollution stopped, there was still increased nutrient supply from runoff and even carried into the Red Sea by dust in the form of nitrate aerosols. These aerosols are produced when our cars and power plants release nitrogen oxide gases, which react in the atmosphere to form nitrate and fall during periodic dust storms that hit the Red Sea a few times per year.

All of these sources of nitrogen are fertilizer for plankton, causing what scientists call “eutrophication.” When plankton blooms, it literally causes the water to be less transparent, which could reduce the clams’ ability to gather light and lead to them growing more slowly. At least that was my hypothesis, but I had to prove if it was true or not. So during that summer and over the next few months, I cut dozens of clam shells into cross-sections, used a special blue dye called Mutvei solution to make their growth lines visible, and took pictures of those lines with a microscope. Then I counted those lines to figure out how many micrometers the clam was growing per day.

A picture showing some of the fine daily lines visible in a blue-stained shell

Here I hit my first challenge: it turned out some clams were putting down one line per day as expected, but some were putting down twice as many! But the way I was using to discern between the two was to measure the oxygen isotopes of the clams’ shells, which forms a record of temperature. By counting how many lines appear between each annual peak of temperature, we confirmed some were daily and some were twice daily. But the oxygen isotope approach is expensive would not be scalable across the dozens of shells I had collected.

Annual growth lines in the shell of a *Tridacna maxima* clam

Then I remembered that I could measure the lines in the inner part of the clams’ shells, which are formed annually. By counting those lines and then measuring the length of the clam, I could get an approximate measure of how much it grew per year on average. This would allow me to calibrate my band-counting and discern which records represented daily lines and which were twice daily! What a relief.

So I went through all of the shells, counting lines and gathering growth info for as many shells as I could muster. It meant many hours staring at a microscope, taking pictures and stitching the pictures together, then squinting at my computer screen highlighting and measuring the distance between each growth line. I had hoped to come up with an automated way to measure it, but the lines turned out to be faint and difficult for the computer to distinguish in a numerical way. So instead I just powered through manually. When I had the raw growth data, I then transformed them to a pair of growth constants commonly used in the fisheries literature to compare growth across populations. When I put the data together across all 55 shells, I was surprised to discover that my hypothesis was totally incorrect. The clams were growing faster!

Growth constants for all three species, comparing fossils and modern shells. We used two growth constants (phi prime and k) to help control for the fact that our clams were at different sizes from each other. You wouldn’t compare the growth rate of babies and teenagers and try to make any broader assumptions of their relative nutrition without some additional attempts to normalize the data!

Science rarely goes according to plan. The natural world is too complex for us to follow our hunches in understanding it, which is the main reason the scientific method came about! But at a human level, it can still be shocking to realize your data says you were totally wrong. So after a few days sitting and ruminating on these results and what they meant, I remembered what Tariq and other scientists had said about nitrates. The clams are essentially part plant. They use photosynthetic symbionts to gain most of their energy. And much as nitrate pollution can fertilize plankton algae growth, maybe it could do the same for the algae within the clams! It had previously been observed that captive giant clams grew faster when “fertilized” with nitrates or ammonia. But such an effect had never before been observed in the wild. We needed a way to demonstrate whether the Red Sea clams were experiencing this.

Fortunately, the clams also keep a chemical record of what they’re eating within the organic content of their shells. Shells are a biological mineral, made of crystals of a mineral called calcium carbonate. But within and between those crystals, there’s a network of proteins the clam uses like a scaffold to build its shell. Those proteins are made of amino acids that contain nitrogen. That nitrogen comes in different “flavors” called isotopes that can tell us a lot about what an animal eats and how it lives. The ratio of heavier nitrogen-13 and lighter nitrogen-12 increases as you go up the food chain. Plants and other autotrophs have the lowest nitrogen isotope values because they use nitrate directly from the environment. For every level of the animal food chain, nitrogen isotope values increase. Herbivores are lower than carnivores. If you live on only steak, your nitrogen isotope values will be higher than a vegetarian. The same will be true for clams. If the clams were taking in more nitrogen from sources like sewage or fish farms, they would show higher nitrogen isotope values in the modern day.

We found that nitrogen isotope values were lower in the modern day!

Taking bits of powder from several dozen of the shells, we worked with technician Colin Carney at the UCSC Stable Isotope Lab to measure the nitrogen isotopes of the shell material. A machine called an Elemental Analyzer literally burns the shell material to release it in a gas form. A carbon dioxide scrubber absorbs the CO2 and carbon monoxide gas, leaving only the nitrogen gas behind. That gas is measured by a mass spectrometer, which essentially separates out the different isotopes of nitrogen and tells us what fraction is nitrogen-13 or nitrogen-12. Plotting all the shell data together, I discovered that my hypothesis was…totally wrong. The nitrogen isotope values of the modern shells were lower than the fossils. The clams had moved down in the food chain, but how?

https://www.israelscienceinfo.com/wp-content/uploads/2017/09/timna-park.jpg — A dust storm rolling over the Israeli Negev Desert. Source

After ruling out a bunch of other explanations including the preservation of the shells, we propose that this represents a human-related change in the environment that the clams are recording. As I mentioned before, the Red Sea these days is regularly hit by huge dust storms which are conduits for nitrate aerosols. Our cars emit nitrogen-containing gases which, through a complex web of chemical reactions in the atmosphere, end up in the form of nitrate particles called aerosols. These nitrate aerosols bind to the dust delivered by strong windstorms called haboobs, which carry the dust long distances, with some of it being deposited several times of year. This deposition of nitrate has been found to form up to a third of the nitrate supply hitting the Red Sea, and was a source of nitrogen that wasn’t available to the clams in historic times. These nitrate aerosols are extremely low in nitrogen isotope value, and would be very likely to explain the lower nitrogen isotope value in our clams! If the clams ate the nitrate, their symbionts would grow more quickly, providing them with more sugars through photosynthesis and accelerating clam growth!

Some additional factors probably also have influenced giant clam growth in the region. The Red Sea historically had regular monsoon rains which likely slowed growth in fossil clams, as storms are known to do for giant clams in other areas, but such monsoons no longer reach the area. The Red Sea also had much higher seasonal range of temperatures in the past, with colder winters and warmer summers. Both factors (storms and extremes of temperature) have been previously shown to depress giant clam growth, and so the modern Red Sea may be a goldilocks environment for the clams: a consistent year-round not too cold or hot temperature.

However, as we discuss in the paper, these factors don’t necessarily mean that the clams are healthier. Faster giant clam growth has been found in other research to lead to more disordered microstructure in their shells, which would have uncertain effects on their survival against predators like fish, lobsters and humans. Additionally, a higher nutrient supply to reefs often causes the corals that build the reefs to lose out to competition from algae that block sunlight and crowd out coral colonies. If the reefs are harmed by the climatic changes that have potentially helped the clams, the clams will still lose. Giant clams are adapted to live only where coral reefs are found, and nowhere else. So more research will be needed in the Red Sea to determine if the health of clams and corals is hurt or harmed by these nitrate aerosols, and what that will mean for their long-term survival in the area.

Over the course of working on this research, the giant clams taught me a lot about life. They taught me that my hypotheses are often wrong, but that’s alright, because my hypotheses can still be wrong in a way that is interesting. I learned to go with the flow and trust the clams to tell me their story through the diaries they keep in their shells. I have followed their lessons wherever they led. Now I am doing follow-up work growing giant clams in a giant coral reef tank at Biosphere 2 in Arizona, to directly observe how the clams’ symbiosis develops and create new forms of chemical records of their symbiosis! The work described in my paper here has led to a suite of different ongoing projects. The clams have many more lessons to teach me. Thank you clams!

Gollum clams

On May 11, 2021May 12, 2021 By Dan KillamIn clamsLeave a comment

Right: Gollum, Middle Earth. Photo credit: Peter Jackson, New Line Cinema. Left: *Congeria kusceri*. Photo credit: Helena Bilandžija

In some ways, living in a cave sounds pretty comfortable. A relatively stable year-round environment and refuge from above-ground predators/competitors make it a place that trogloditic (cave dwelling) animals can develop stable evolutionary forms which persist through long periods of time. Like the deep sea, caves are great places to look for “relict” organisms representative of groups that disappeared long ago on the surface. But living in a cave presents a lot of challenges that require specialized adaptations. The most obvious is the lack of light, the source of energy for photosynthesis supports food webs on the surface. Animals in caves must make a living eating material that flows in from the surface world, like bat gauno or debris from runoff. They can also make a living eating the microbes that directly feed off the rocks of the cave walls. Some caves also have methane or other geologically sourced gases that can serve as a food source, similar to the deep sea, where methane seeps and hydrothermal vents provide fuel for diverse and vibrant ecosystems.

A map of the 15 caves where *Congeria* has been found. Source: Bilandžija et al. 2013

You don’t need to watch Lord of the Rings to see that spending your life in a cave like Gollum requires serious changes to your lifestyle. But that’s exactly where we can find an unusual genus of freshwater mussels called Congeria. Congeria consists of three species found so far only in fifteen caves in the Dinaric Alps, a mountain range in Southeastern Europe stretching from Italy to Albania. These mountains are made from limestone that first formed at the bottom of a shallow tropical sea (picture the Bahamas and you get a good idea of how it would have looked) during the Mesozoic era, the time of the dinosaurs. This limestone (also called karst) was lifted up in the early Cenozoic (after the Cretaceous extinction) by tectonic activity due to the collision of the Adriatic microplate with Europe. This 645 km-long row of mountains is made of a highly soluble rock similar in chemical composition to Tums. Over millions of years, cracks in this karst have been widened by acidic rainwater dissolving away the limestone to make caves. The Dinaric Karst is chock-full of such caves which form a huge maze of interconnected systems deep into the earth (the limestone goes down for kilometers into the crust)!

*Congeria kusceri* shows its white, unpigmented flesh. Photo by Vedran Jalžić

So if you were to put all your cards into evolving to be a cave creature, the Dinaric Karst would be a great place to try it. All sorts of spooky trogloditic creatures are found down there, such as olm salamanders, cave-dwelling isopods (rolly-pollies), and more. But Congeria is of particular interest because it is a remnant of a group of mussels that was once much more prevalent across this area of Europe, once a huge mass of swamps and lakes called Paratethys. Many species of mussels in the same family as Congeria can be found as fossils in rocks covering an area reaching from Switzerland to Lake Aral in Central Asia. But over time, the climate and geography of the area changed and almost all of these species went extinct. It was once assumed that Congeria had itself gone extinct 5 million years ago, as it was only known from fossils.

*Congeria kusceri*. Photo by The Croatian Biospeleological Society

In the 1960s, a team exploring the caves of the Dinaric Karst were shocked to find examples of living Congeria in caves. In many ways, the story was very similar to the discovery of coelocanths in the deep sea, a fish assumed to have gone extinct millions of years ago which was found by accident. These species are remnant twigs of previously lush branches of the tree of life. Such species are sometimes called “relict” taxa, or sometimes “living fossils.” Many biologists prefer not to use that phrase, because while these creatures may closely resemble the forms of their distant ancestors, they often have changed in all sorts of ways not easily visible to the naked eye. Congeria was unknown to us, but spent millions of years evolving to improve its fitness in its cave environment. Such groups thought extinct only to reappear later in the fossil record are also sometimes called “Lazarus taxa.” Like Lazarus in the biblical story, Congeria was thought dead only to reappear much later.

It appears the species making up Congeria were trapped in Paratethys first by the rise and retreat of the Mediterranean Sea and then trapped in caves following the drying up of Paratethys. For the past several million years, they have lived only in the cave systems of the Dinaric Alps. But like Gollum, they were not preserved exactly as they previously lived in the Paratethys. While other freshwater mussels continue to frolic like merry hobbits through the streams of the Dinaric Alps above, Congeria has adapted in all sorts of interesting ways to its life as spelunking animals.

Like other bivalves, Congeria makes a living filter feeding. But in caves, they don’t have access to the photosynthetic plankton food that is the main dietary staple for typical bivalves. Congeria instead feeds on whatever detritus flows its way through the waters of the caves, and it can’t be picky. Bivalves use their gills to catch food when filtering, and Congeria has a particularly bulked up set of gills to supercharge its ability to grab these particles. But the palps, organs to select which particles to actually bring to the animal’s mouth, are tiny to the point of being almost absent. As with Gollum, who was known to gobble down the occasional goblin, Congeria can’t be selective. They have to try to eat whatever comes its way, unlike other bivalves such as my Biosphere 2 clams, which spit out many of the particles they catch as “pseudofeces.”

In evolution, if you don’t use a feature, you often lose it. Organisms can’t afford to be sentimental about organs; if it saves energy and doesn’t cost any survival ability to cut out a particular feature, it will be reduced or lost over the generations. Like other cave animals, Congeria has lost almost all pigmentation since such pigments have no purpose in the absence of light. It also has a highly reduced foot, which is used by other freshwater bivalves to move around and dig in the sediment. In the stable, low energy environment of caves, a muscular foot would be a waste of energy. It has lost its statocysts; balance stones similar in function to our inner ear used by most mollusks to sense which direction is up. Since it settles on any available surface and doesn’t move, it makes sense to strike that item from the energy budget.

*Congeria* living comfortably out of water, one with valves open! Source Glavaš et al. 2017

Most bivalves in the freshwater mussel Dreissenidae family are “r strategists“, meaning they are like guppies or mice, producing and broadcast spawning a huge number of offspring. They don’t put too much energy into each offspring, and hope a certain small percentage of them will survive each year to keep the cycle going. R strategists often don’t live very long. Such a life strategy would be tough to sustain in isolated cave systems, which are a harsh environment in many ways, particularly regarding food supply for baby Congeria. Congeria instead has evolved to be a “K strategist” like humans or elephants. It “broods” its young rather than broadcast spawning. This process, found in other bivalves from extreme environments such as polar regions, involves taking in sperm to fertilize eggs internally. The mother clam then nurtures the embryos to a certain size, first within the gills and then in special pouches in the mantle tissue. This organ is called a marsupium; these clams are like kangaroos! Brooding is much more energy-intensive than broadcast spawning, since the mother is sharing energy with her babies, but the investment ensures that each baby Congeria will reach a larger size before leaving its mother’s shell, giving each one a better chance of surviving long term. In the resource-deprived environment of a cave, a little boost to reach maturity matters! Because real estate is fairly limited in its caves, Congeria can survive in very dense aggregations with over 1,600 individuals per square meter. These mussels are surprisingly selfless and communally living for such a harsh environment.

An acetate peel of the hinge of *Congeria kusceri*, showing annual growth lines used to tell its age. Source: Puljas et al. 2014.

As with Gollum, Congeria has become very long-lived. Individuals have been confirmed to live almost 60 years based on growth lines in its shell, and there are suggestions that they can live much longer. In the relatively predatory-free environment of the caves, Congeria can bet on not being killed before it reaches its prime. Instead, its greatest enemy is the fickle environment of the caves, which are dependent on water flow from the surface. Their shell growth is interrupted during the summer, when the waters of its cave become much less alkaline than at other times of year, depriving them of the calcium they need to build the shell. At other times they might have to survive extended periods being emersed from the water, when levels drop during the dry season or droughts. Most bivalves can only persist for hours in such conditions, but Congeria can survive 2 months out of water! For Congeria, it makes sense to bet on being able to survive as long as it can in the spot it settled, trying to reproduce little by little over a long period of time. In this way, it is not quite like Gollum, as it has evolved to live a long time to improve its ability to reproduce and pass on its genes, rather than out of selfish worship of a ring.

Like Gollum though, Congeria is very unique and fragile. The caves in which it lives are a sensitive environment, vulnerable to overdevelopment and pollution. Manipulation of groundwater has reduced the flow of water through these caves and thus restricted Congeria‘s habitat, wiping it out from areas of some caves. Because its population is inherently restricted by the “small pond” it inhabits, it would not take a big environmental disruption to wipe Congeria off of the map. To that end, Congeria is red-listed as endangered and is protected in most of its native countries. Still, we can only hope that even now there are other populations of Congeria waiting to be discovered, hidden in unexplored caverns deep in the Dinaric Karst.

Recent Science Communication!

On March 26, 2021March 26, 2021 By Dan KillamIn academia, scicommLeave a comment

At Biosphere 2, our science is essentially done in public. Every time I’m in the water checking on our clams and the sensors around them, I’m in view of the public and essentially an attraction for the public to watch. This is a really unique way to do science unlike any of my past experience, when I’ve been out in the field with a collaborator, or in the lab with a laboratory technician. I was initially intimidated by the idea of doing my science with an audience, but I’ve decided to lean into it as a huge opportunity. It is rare that the public gets to see all the steps going into our science; they usually only see the end of the story and not the whole journey leading up to that point. So recently I participated in two new ways of sharing my work while it’s in progress with the public.

The first was a collaboration with Mari Clevin, a videographer with the University of Arizona who made a really nice profile of my crazy clam journey. It was a lot of fun showing her around B2, trying to capture what it’s like to work here. It was fascinating seeing how all her footage and interviews came together into a video, and how she captured the key points of our conversation into a narrative!

The other scicomm event I participated in was a “Research Show and Tell” event run by the PAGES Early Career Network. Early Career Researchers include PhD students, postdoctoral researchers like me, and early career faculty. The ECN is intended to help us band together to share opportunities and plan events relevant to our interests. Among the North American regional representatives for the ECN, we saw a real need for more informal ways to share our research to an advanced audience of our peers. We’re all burned out from Zoom webinars, and on the other side Zoom coffee hours don’t typically provide much opportunity to share scientific content, so there’s a real need for events in the middle. So I was excited to share my research with a group of my peers, touring them around the Biosphere, showing them my clams via pre-recorded video and then having a Q and A to describe the work. It was a lot of fun and you can watch the whole hour-long event below!

Biosphere 2 Update!

On September 27, 2020September 28, 2020 By Dan KillamIn Biology, clams3 Comments

I am now several months into my postdoctoral fellowship at Biosphere 2 in Oracle, Arizona! I am working with Professor Diane Thompson on a project measuring the shell and body chemistry of giant clams in Biosphere 2’s huge reef tank. Our goal is to find better proxies (indirect ways of measuring) the symbiosis of these clams with the algae they farm within their bodies. The controlled, closely monitored conditions of the Biosphere 2 ocean tank represent the perfect balance between the real ocean and the more controlled environment of a lab. Using trace metals and isotopes in their shells and tissue, we can trace back the ways that clams record their own internal biology. Wild giant clams make chemical records via the growth lines in their shells, similar to tree rings. These have been the subject of many cool past studies, but there are aspects of the “language” they use to write their shell “diaries” that are poorly understood. Much like researchers used the Rosetta Stone to decode heiroglyphics, we are observing clams as they grow in order to better translate the shell diaries of their prehistoric ancestors. Doing so, we can better understand how their ancestors reacted during past periods of climate change, and identify similar bivalves in the fossil record which may have harbored symbionts.

I started my postdoc remotely in May. The following months were spent sheltering at home in Southern California with my mom, supervising the installation of a cohort of giant clams into the 700,000 gallon ocean tank over Zoom. It felt like a science fiction movie, watching technicians Katie Morgan and Franklin Lane from hundreds of miles away on my computer screen as they nurtured and installed the little clams in their new home. I felt like Mission Control back on earth, watching a group of space colonists work with strange alien creatures.

Some of the *T. derasas* in the Biosphere tank

But in August I was able to finally move to Tucson to meet these clams in person! We had three species in the first batch: Tridacna derasa, T. squamosa and T. maxima. Of the three, T. derasa (the smooth giant clam) has proven to be the most successful in the Biosphere 2 ocean tank. All of the derasa clams from May have survived and thrived, attaching themselves to the bottom with byssal threads and growing their shells, both very positive signs of clam health!

Some of our newer batch of *T. derasa* in the quarantine tank

So we have doubled down on T. derasa and installed 11 more individuals last week, sourced from Palauan clam farms via a reef supply company in Florida called ORA. They are currently in a shallow quarantine tank where we will monitor them for disease and unwanted hitchhikers before introducing them to the broader Biosphere tank.

The workers at Biosphere 2 are very creative problem solvers. Giant clams need intense amounts of light to sustain their symbiotic algae and create food for themselves, a quantity of light higher than is available in the current Biosphere tank. To provide a light supplement, the engineering team at Biosphere 2 constructed a floating lighting rig with hanging LED lighting, right over the lagoon where we have the clams!

The lighting rig glows with a blue light as the sun goes down outside the Biosphere

To make sure the clams have enough light, we installed a Li-Cor light sensor to measure the exact amount of photons (light particles) hitting the clams over the course of a day. The light is measured in units of micromoles of photons per meters squared per second. A mole is 6.02 * 10²³ particles, and other clam experts like James Fatheree have suggested that the clams need light levels of at least 200 micromoles/m²s to make enough food for themselves. That’s 120,400,000,000,000,000,000,000 light particles we need to hit every square meter of their habitat every second. The clam channels as many of those photons as it can to its algae residing within tubes in its tissue. The symbionts use it in photosynthesis to make sugars, which they share with their host. A well lit giant clam is a happy, well-fed giant clam! But because the glass dome of Biosphere eats up some of the light, and plankton and floating particles in the seawater eat up another portion, we use the lights to make sure the clams have the boost they need to maintain their symbiosis like they would in the clear, shallow waters of a tropical coral reef.

The Li-Cor sensor floats above the clams, telling us how much light they’re getting

Much like a new dad might read parenting books to get ideas for baby care, I am always poring through the literature trying to figure out how to maximize the growth of these clams. Dr. Fatheree is kind of like Dr. Lipschitz from Rugrats, except unlike the suspect childcare advice in the show, this real-life giant clam advice is very valuable. Like human babies, these clams can be a challenge! The clams sometimes decide to move around and get themselves into trouble, requiring us to rescue them if they get trapped behind a rock or under a pile of sand. So I have had to do a fair amount of clam-herding during my time here.

We are growing the clams for science, and there will be data to collect. We will be monitoring data like the trace metal chemistry of the clams’ tissue and shells, the color of their mantles, and the pH, temperature and oxygen levels of their environment, all to relate together to make the best clam record of their environment possible. So far, I have been snorkeling in the tank every couple days maintaining their setup. Next week, I will dive in the Biosphere tank for the first time to collect data on their shell chemistry! I have other projects in the works to measure their valves opening and closing using magnetic sensors, and to measure their color changes through time through computational photography.

That brings me to what I’ve found to be the coolest part about Biosphere 2: the people. Something about this place attracts creative, brilliant, can-do people who solve problems on the fly and are always jumping into the next project. It has been a privilege to learn and pick up technical skills from them in the brief time I’ve been here. This place is really like a space colony out of The Expanse or Silent Running. There are endless valves, pipes, tanks, exchangers and other hardware needed to keep Biosphere 2 running. Getting to witness the technical competence behind the whimsical solutions the staff comes up with, like the floating light rig, has been the most exciting part of this job for me. Everyone has a deeply ingrained curiosity and passion for science that is inspiring to see; they are as interested in my clams as I am in their corals, tropical plants, and geochemical experiments. I would argue that the human team behind Biosphere 2 is a bigger treasure than the unique metal-and-glass structure they work under, and I look forward to seeing the results all of the collaborations we have in the works!

Research Explainer: The chemistry across a “forest” of giant clams

On July 19, 2020July 20, 2020 By Dan KillamIn clams8 Comments

Another one of my PhD chapters is published in the journal G-cubed, resulting from work I did in the summer of 2016 in Israel and Jordan around the Red Sea. This is my first geochemistry article in a journal, so it is a big deal to me! I thought I’d write up a clamsplainer about what I was looking for and how we went about achieving the paper.

A slice of giant clam shell. You can see the difference between the inner and outer layers. The inner layer has visible annual growth lines.

I study the chemistry of giant clam shells. You might already be familiar with the concept of tree rings, a field called dendrochronology. It’s like reading the diary of a tree, where every “ring” is a page in the record of its life. The related field of sclerochronology looks at rings in the hard parts of shelled organisms. We can count those rings to figure out the ages of clams, or their health, and we can measure the chemistry of those rings to understand the temperature the clam grew at, and even what it ate.

A giant clam growing on the reef flat in Eilat

Giant clams are bivalves of unusually large size which achieve a very rapid growth rate through the help of symbiotic algae in their flesh. The clams are farmers, and their crop is inside their tissue! They grow their shells very quickly (sometimes up to 5 cm a year, equivalent to if a six foot tall man grew a foot every year from birth), and live a very long time, up to 100 years (their growth slows later in life). A whole bunch of talented researchers have measured the chemistry of giant clams all around the world to reconstruct past climate and even measure historic storms!

If we want to understand the ecology of a forest, we can’t measure just one tree!

But if you come back to the analogy of tree rings, we essentially have measured the rings and chemistry of individual “trees” in a bunch of different places, but don’t have as good an idea of how the chemistry varies within a “forest” of giant clams in a particular place. In our new study, we set out to describe exactly that, focusing on the Northern Red Sea.

A map of the Northern Red Sea. The right “toe” is the Gulf of Aqaba

Sites where we sampled shells along the northernmost tip of the Gulf of Aqaba

The Gulf of Aqaba represents the northernmost toe of the Red Sea, bordered by Egypt, Israel, Jordan and Saudi Arabia. It hosts some of the northernmost coral reefs in the world, aided by tropical temperatures and clear waters due to the lack of rainfall in the surrounding deserts. Here, we can find three species of giant clams including the small giant clam Tridacna maxima, the fluted giant clam T. squamosa and the very rare T. squamosina, which is found only in the Red Sea and nowhere else (as far as we know). In summer 2016, I went all around the Gulf of Aqaba collecting shells of clams from the beaches, fossil deposits, and even were able to work with shells confiscated from smugglers at the Israel-Egypt border. We cut these shells into slices and used tiny drill bits to sample powder from the cross section of their shells, which we could then conduct geochemistry with! We sampled large areas in bulk from the inner and outer portions of the shell (more on why later) using a Dremel tool, and also sampled more finely in sequential rows with a tiny dental drill bit (same brand your dentist uses!) to see how the measured temperatures varied through seasons. By “we”, I mean my coauthor and friend Ryan Thomas, who spent every Friday morning for several weeks milling out most of the powder we needed for this study. This data became part of his senior thesis at UCSC!

Two giant clams thriving on the shallow reef near Eilat, Israel

What kind of chemistry did we measure? The shells of clams are made of calcium carbonate, the same stuff Tums is made of. Calcium carbonate contains one calcium atom, one carbon atom, and three oxygen atoms. It turns out that all of those atoms come in “flavors” that we call isotopes, relating to the weight of those atoms. When you take the shell powder and put it into a machine called a mass spectrometer, you can figure out the proportions of isotopes of different elements present in the samples

The first isotope “flavors” we were interested were carbon-12 and carbon-13. The ratio of the two is thought to relate back mostly to the action of the algae inside (its symbionts) and outside the clam’s body (the floating algae the clam filters out of the water as an additional meal). This happens because as algae take carbon from the environment and bind it into sugars through photosynthesis, they naturally weight the dice in favor of carbon-12 making it into the sugars. So carbon-13 is left out in the water, and potentially in the clam’s shell. When photosynthesis is more active, it would leave the shell with proportionally more carbon-13. At least that’s what other researchers have confirmed happens in corals, and suspect happens in clams. In the world of isotope chemistry, this phenomenon is called “fractionation,” when a process causes isotopes to form fractions separated by mass. We wanted to test if that was true for giant clams, and could do so by comparing T. squamosina and T. maxima, which have more active photosynthesis, to the less photosynthetic T. squamosa.

Comparing carbon isotopes across different species and shell layers. The results are fairly flat all the way across.

It turns out that the more symbiotic species don’t have more carbon-13 in their shells. We set out several reasons that might be the case, including that the symbionts of these clams are actually more carbon-limited than many researchers might expect. Essentially, the algae lack an excess of carbon atoms to choose from, so they can’t be picky with which isotopes they use to make sugars. Therefore, the fractionation effect weakens and becomes possibly too subtle to manifest in the shell, even in the best-case scenario of three closely related species living the same area. This represents what I’d term a “null result.” We had a hypothesis and we demonstrated that hypothesis was not the case in our data. It was important to publish this result, because other researchers will know not to try the same thing. This means that when we try to search for evidence of symbiotic algae in fossil clams, we will likely need to use other types of chemistry to figure it out. But don’t worry, as finding such a “smoking gun” for algal symbiosis in fossil bivalves is part of my life’s work! I have a few projects in the works looking for exactly that kind of evidence! 😉

A look at how temperatures measured via oxygen isotopes vary through the lives of the animals. This is how scientists can use very old shells to figure out how temperatures varied through a year in prehistoric times!

But we had additional data we collected in addition to the carbon isotopes which actually turned out to provide some interesting results. This other type of measurement regarded the oxygen isotope ratio of the shells. Previous research has shown that the ratio of oxygen-18 to oxygen-16 in carbonate skeletons directly relates to temperature, a principle that has birthed a field known as paleothermometry. There are thousands of papers which use shells of corals, clams, cephalopods, microbes and more to reconstruct temperatures in ancient times. Giant clams have proven to be effective weather stations going all the way back to the Miocene epoch, millions of years ago! Because they grow so quickly (putting down a new layer every day), live for a long time, and don’t stop growing, they form very complete, high-resolution, and long records of past climate.

But no past studies had ever compared different species of giant clams from the same place. There would be interesting new lessons to draw from such a comparison, including seeing if one species preferred to grow at warmer parts of the reef. As complex, three dimensional structures, there are many remarkably different micro-environments throughout a reef, from the hot, sun-exposed reef flat and crest to the cooler, current-swept, deeper fore-reef. Do any of the species of giant clams show a consistently higher temperature than the others, and what would that mean if they did?

*T. squamosina* records higher temperatures than the other species. Outer shell layers also record higher temperatures than inner shell layers. More on that later in the post 😀

It turns out that the rare T. squamosina, only found in the Red Sea, does record a higher average temperature, almost 3 degrees C higher than the other two species. This is of interest because this species had been proposed by prior researchers to only live on the sun-drenched reef crest, at the shallowest part of the reef. We believe these results corroborate that observation. The previous research on the habitat of T. squamosina was limited to a single study which only was able to find 13 live animals along the coast of the Red Sea. But by independently confirming this life habit, we can ask further questions that may be borne out by further research.

An example of *T. squamosina* showing signs of possible bleaching (light parts at the center of its body).

Being restricted to the shallowest waters, is T. squamosina at greater risk of harvesting by humans along the shores of the region than its counterparts? Illegal poaching of giant clams along the Red Sea is believed to be a major stressor on their population size in the area. Could this explain why T. squamosina is so rare today, despite being proposed to have been more common in the past? In addition, being restricted to the top few feet of depth in the water could leave the species more vulnerable than the others to atmospheric warming. As with corals, when giant clams overheat they will “bleach”, expelling their symbiotic algae as a stress response. While the clams can recover, it is sometimes a fatal form of stress that leads to their death.

An excellent cartoon of the different shell layers in giant clams. From a peer of mine who also studies them, Michelle Gannon!

More research is needed to answer those questions. But the last aspect of this study relates to what is happening inside of the bodies and shells of the clams themselves. Giant clam shells have two layers. The outer layer grows forward away from the hinge, increasing clam’s length. The clam also makes an internal layer, growing inward to thicken the shell and add weight. We can read the growth lines of the clam’s diary within either layer, and different studies have used one or the other to make records of climate change. But very few studies have compared the two layers of the same individual. Do they record the same temperatures? Figuring it out would be important to determine how studies with just the inner layer or outer layer can be compared to each other across time and space.

A vividly blue example of the small giant clam, *T. maxima*. From user arthur_chapman on iNaturalist

In our studied clams, it turns out that the outer layer records warmer temperatures on average than the inner one! After ruling out other possible explanations behind this difference (the details are complicated and hard for even shell nerds to wrap our heads around), we settled on the idea that the outside of the clam is indeed warmer on average than the inside! This means that the outer layer, recording temperatures of the outer mantle, is indeed forming at a higher temperature than inside! Why is this?

Unlike us, clams are ectothermic. They generally stay the same temperature as their surrounding environment and don’t use their metabolism to generate internal heat. But that doesn’t mean that the clam doesn’t have hotter and cooler spots in its body. It makes sense that it would be hotter at the outer part of its body, facing the sun, as the solar rays hitting its outer mantle would then radiate out again as heat. The outer mantle is also darker in color than the inner mantle, allowing it to absorb more solar energy, much as you might feel hotter wearing a darker t-shirt in the sun than a white one. Photosynthesis itself produces a warming effect, a phenomenon known as non-photochemical quenching, and so the outer mantle, which contains the vast majority of the symbiotic algae, may be partially warmed by the activity of the symbionts!

More research is needed to confirm if this is true. As of yet, no researcher has ever stuck a temperature probe in multiple parts of a clam to see if the outside of it is indeed warmer than the inside. But until that day, it is interesting to think of how this would influence comparisons of diaries from the inner and outer layers of different bivalves. The effect is on the small side, so it doesn’t really mean one layer or the other should be preferred for future shell-based studies of climate change. But it could be an additional aspect to consider in the future as a way to record temperature differences within the body of an animal, and look into how those differences influence its overall level of stress.

Examples of juvenile smooth giant clams, *T. derasa*, that we’re growing at Biosphere 2. Photo by Katie Morgan.

So I hope this long explanation of my paper helps you to have a better idea of the work I did during my PhD thesis. There were other aspects to the paper that are too wonkish to get into here, particularly concerning the correlation we found between carbon and oxygen isotope ratios, but if you have questions or want a copy of the PDF, please message me! I have more clam papers in the pipeline, and my new postdoc at Biosphere 2 involves growing three species of giant clams in a controlled environment, where I hope to answer some of the physiological questions I mentioned above! But until then, stay hinged and happy as a clam (as much is possible in this chaotic time), and take comfort knowing there are colorful bivalves out there all at this very moment, harvesting sunlight for food and growing huge shells.