Israel: Field Report!

So I’ve been living in Israel since the start of November after a whirlwind of defending my PhD, moving out of Santa Cruz forever and suddenly moving to another continent for a postdoc. I’ve been working on clams, taking samples, using an SEM and planning a new manuscript, but I have also been learning a lot about living in a country that is at once strangely familiar and completely foreign. I’m coming back to California tomorrow for a Holiday break, so I took an hour to reflect on what I’ve learned about this country so far. Here are some random things I’ve learned about Israel during my time here.

Israel is small

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Israel is a tiny country by my Californian standards. You can take a bus along the entire length of it in less than seven hours. I am in Haifa on the farthest northern part of the Mediterranean coast, but in 2016, I lived down in Eilat for two months. Despite its small size, Israel has a variable climate depending on where you are. Up in Haifa, they have have a classic Mediterranean climate which reminds me of California in a lot of ways (think chaparral and coastal dunes, though a little more humid than I’m used to and with more thunderstorms). The Negev desert is in the South, which is intensely dry, hot and sometimes completely devoid of vegetation.

Happy naturalists!

For birders, I’ve noticed the North is dominated by hooded crows from Europe while the South is dominated by house crows, an Asian species. In general, because they’re at the nexus between Europe, Asia and Africa and the gradient between those ecoregions, Israel and the Middle East overall are very biodiverse. As a result, there is a vibrant culture of naturalists in this country who want to know about every aspect of every species. When I post something to my iNaturalist, within a few hours someone who is an expert on that taxon confirms or corrects me, without fail.

Delicious food+drink

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Living here, I have been subsisting of a diet based largely on hummus, falafel, shawerma, tahini (try the dark kind!) and pita, with plenty of veggies thrown in. In fact, there are restaurants where they just serve you a bowl of hummus with pita and you have at it. Be prepared for the food coma. For beers, I guess Danish beer companies got a big foothold here early on because the defaults are Carlsberg, Tuborg, Heineken etc. The biggest native Israeli brewery is Gold Star, and they’re not bad! And there are a growing number of Israeli craft breweries. Overall I approve, though they sometimes experiment a bit too much and taste odd, and a lot of them don’t really seem to know what an IPA is.

Cultural diversity

Israel, as you may or may not have heard, is indeed a very complicated place. There is no doubt that the tensions are high between Israelis and Palestinians and Hezbollah and Iran, which is often in the news. But day to day on the ground, Israel is a very safe place and safer than what I’m used to in the States. The crime rate is much lower than almost everywhere in the US, and I can walk around Haifa at night without ever feeling at risk. That is more than I can say for Santa Cruz and many parts of LA.

Haifa is a special place. It is a uniquely diverse city with a significant Arab population. The student body at the University of Haifa is over 30% Arab in descent and I can walk through hearing four languages in one hallway. The main temple of the Baha’i faith is here in Haifa.

There are Israeli Jews of all sorts of backgrounds, including Ashkenazi, Sephardic, Yemeni, Ethiopian and more. There are secular Jews, Conservative Jews, Orthodox Jews and the Haredim (Ultra-Orthodox), along with myriad others I haven’t learned about yet. There also is a huge population throughout Israel of Russian Jews who came here following the collapse of the Soviet Union. Russian is spoken heavily here and is on the street signs. Like America, Israel is a hugely diverse place and I believe could be a great strength for their future growth and prosperity.

Language and cultural challenges

As a secular American, there were some parts of Israel that have proved challenging to adapt to. The biggest challenge for me by far is that Israel’s national language is Hebrew, which is a very challenging language to learn. I now know the numbers, some letters and some words, but there’s no way I’m going to be able to pick up conversational Hebrew during my time here. And as all foreigners know, not being able to read and write makes literally everything about “adulting” more difficult. I have had to learn never to assume that English is understood here. I speak slowly and use hand gestures. I do everything in person, never over the phone. Trying to do something logistical over the phone has not once worked. Seriously, don’t even entertain the notion of trying to do stuff in English over the phone here.

Instead, I recommend going to the place you need to go, ask the person for help with a dumb blank smile on your face, and people will try to help you do what you need to do, whether that is opening a bank account, getting your bus card, or signing a lease for your apartment. People here are generally very direct and no-nonsense in everyday business dealings, but they also have proven very generous and willing to help me, which is not something I can say about service in America. However, on the rare occasions when I’ve found someone who speaks English, is available, and is exactly the person who can help me with the task at hand, I feel as though I should drop to my knees and thank the God of Abraham for his mercy. Day to day life here is tough for a non-Hebrew speaker.

If there was one aspect of life in Israel which I will openly complain about, it is Shabbat (from sundown Friday to sundown Saturday). In most of the Western world, we take for granted that Saturday and Sunday are the days of rest. But here in Israel, it is Friday and Saturday, and Israel is very hardcore about their days of rest. On Shabbat, any eating establishment that wants to be Kosher has to be closed. Almost all public transport is shut down.

There are a small number of more secular, diverse cities, luckily including Haifa, where a couple buses stay running Friday night and Saturday. But on Saturday, if I realize I need groceries, my choice is to splurge on a cab or walk 25 minutes down to the nearest 24/7 market (basically a convenience store). There is a reason Shabbat is a big deal in Israel and I get it. There is no other country on Earth where Jews of all creeds and colors can know that they will get to observe Shabbat in the way it was practiced by their ancestors. But for me as a secular person without a car, it presents a lot of logistical challenges.

Miscellaneous

Here is a list of other things I found notable and unexpected about life in Israel

  • They really like malls. There are new malls opening everywhere and they are always full of people. As an American, I think of malls as very last century, but they’re still the main social place here for many people.
  • They don’t really use mops. Instead, they use giant squeegees to clean their floors. I still don’t get how to use one.
  • When you sign a lease, many landlords want twelve pre-signed checks. I thought this was very strange (where do they keep them?!) and then noticed an option in the ATM to save checks for “safe-keeping.” Weird.
  • Israel is a cell phone paradise. I can get an unlocked SIM card with 30 gb of data, unlimited voice and text for $21.50. This is absolutely insane. How is this possible?
  • In Israel, they charge tenants a bimonthly property tax. That is annoying!
  • People say Israel is super expensive and yes, prices on food and basics are somewhat high by standards of some US States. But coming from California, I have been so relieved. I now can afford to live in my own apartment and pay <25% of my income on rent rather than 50%. I can once again stay under $10-15 a day on food which wasn’t possible for me in California for the last couple years. So I have more discretionary income for fun stuff which has been refreshing.
  • As I’ve noticed in Europe as well, it’s fun paying with coins! They have 10, 5, 2, and 1 shekel coins and I find myself actually using them, unlike the useless pocket change in the states that I just save to trade in later. There are around 3.7 shekels to the dollar.
  • They have an excellent bus system (except Friday or Saturday 😉 ). Buses come by frequently in all parts of Haifa, are clean, and cost about $1.50 per ride (1/3 less than that if you set up your student access card). The bus card allows you to connect for free within a certain time period as well.
  • Most locks in Israel use keys on the inside and outside. I’m not sure if this is an Israel-specific thing, or just something the rest of the world has that the US doesn’t, but it was surprising to see that I’d have to use my key to lock my front door from inside.
  • They have smarter crosswalks in Haifa that generally bridge over a median, with two separate pedestrian lights. You may have to stop in the middle but it means less risk of someone doing a turn and hitting you, and that is good urban planning in my book. Eilat has done away with streetlights altogether, completely converting to roundabouts. I frickin love roundabouts.
  • Israel has a semi private system of healthcare, but with generally very high quality care and low cost.
  • In Israel, life is completely transformed by their mandatory military service. While I have been out of college for a few years, many Israelis are only just starting college as they enter their late 20s after being discharged. So the student body trends older at Israeli universities.
  • I thought I’d stick out as an American goy being here, but apparently I don’t. People keep asking me for directions in Hebrew and Russian and I just say “sorry, English only”, and they look at me with disappointment. I guess I can say I look Jewish!

In conclusion, I have enjoyed my time in Israel so far, and I have found myself just watching life going on around me with great curiosity, because it is a very interesting place full of constant unexpected moments. Let me know if any of you visit anytime soon 🙂

Mystery of the “spurting” mussels

If you’ve read any of my posts, you should realize by now that clams are pretty weird. Some catch live prey. Some have algae in their bodies that they “farm” for food. Some can bore into hard rock. Some sail the seas on rafts of kelp. Clams live in a competitive world and have had hundreds of millions of years of time to evolve to try out all sorts of weird, unlikely ways of life.

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U. crassus in a Slovenian river (Alexander Mrkvicka)

The thick shelled river mussel (Unio crassus) is known from many rivers and streams of Central Europe. As this is a very well-studied region of the world, many generations of academics have noted an unusual, seemingly inexplicable behavior undertaken by these mussels at certain times of year.

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U. crassus propped up on its foot (UCforLife)

Using its muscular foot, U. crassus pulls itself to the edges of the streams and rivers it lives in until it is partially exposed to air. It orients itself at a right angle with the surface of the stream with its siphons (two little snorkels coming out of the shell) facing out towards the water. Like all bivalves, U. crassus can act as a bellows by opening and closing its shell to pull in and push out water through those siphons. It has one siphon above the water and one below, and it proceeds to suck in water and spray it into the center of the stream using the power of its suction. The water can travel over a meter away and they continue this spurting about once a minute, sometimes for hours.

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Squirting water into the stream! (Vicentini 2005)

Needless to say, this is a very strange and unlikely behavior to observe in a mussel. It is exposing itself to potential dessication or suffocation from exposure to air. It is vulnerable to predation from terrestrial mammals and birds. There has to be a very powerful benefit from this behavior to outweigh those risks. And why squirt water into the air?

Some researchers proposed that the mussels were traveling to shore to harvest from the more plentiful food particles deposited there. But why would they face their siphons away from the shore then? Other workers suggested that it was a way to reduce heat stress through evaporation, though that also seems unlikely, considering the water is warmest in the shallows. The question persisted for decades in the minds of curious malacologists.

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Top-down view of spurting behavior (Vicentini 2005)

In 2005, Heinrich Vicentini of the Swiss Bureau for Inland Fisheries and Freshwater Ecology decided to try settle the question of why these mussels spurt. He observed several dozen of the mussels crawl to the edge of the water and diligently begin squirting into the streams. In the name of science, put himself in the path of these squirts, caught the water and used a hand lens to observe that the squirted water was full of mussel larvae (glochidia).

Lifecyle of U. crassus (Rita Larje via UCforLife)

U. crassus falls in the order Unionida, a group of freshwater mussels distinguished by a very unusual method of reproduction. They are parasites! Because they can’t swim well enough to colonize upstream against the current, they need to rely on fish to hitch a ride. Some have evolved elaborate lures to convince fish to take a bite, then allowing them to release their larvae, which attach to the fish’s gills like binder clips and ride all the way upstream. Once they have reached their destination, they detach and grow up into more conventional burrowing mussels. It’s a weird, creepy and wonderfully brilliant strategy that enabled the mussels to invade the inland rivers which would otherwise be inaccessible to them.

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Loach (type of freshwater fish) gills with unionid larvae attached (UCforLife)

The mussels appear to be spurting out not only water, but their babies. They gain a couple of advantages from this. For one, their larvae can distribute further than would be possible from the bottom of the creek. Instead, they are released at the center of the surface of the stream, where they can be carried for a much longer distance by the current before they settle at the bottom. In addition, the splash of water on the surface may mimic the behavior of insects and other fish food falling in the water. A curious minnow might venture to investigate the source of the splash, where it would promptly breathe in a cloud of larvae that get stuck on its gills. A pretty rude surprise, but a brilliant trick to give the baby mussels the best chance of surviving.

So again, clams prove themselves to be far more clever and interesting than they might initially seem. U. crassus and other members of the Unionida are an ancient and globally distributed lineage which have evolved all sorts of weird and wonderful ways to maintain their river lifestyle. Unfortunately, rivers are some of the most widely damaged environments in the world. A majority of freshwater mussel species worldwide including U. crassus are endangered by habitat loss, overharvesting and pollution. But more research into their unusual biology can help us understand ways we can enhance their conservation, with the hope of providing more habitat for them to recover populations in the future. New projects in Sweden and other countries aim to recover habitat for their larvae to settle along 300 km of rivers, and research the fish species which their larvae prefer to hitch a ride on. With more work, we can hopefully ensure that the streams of Europe will harbor little mini super-soakers for millennia to come.

The clams that sail the seas on rafts of kelp

 

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The streamlined shells of Gaimardia trapesina. Source: New Zealand Mollusca
Bivalves are not known as champion migrators. While scallops can swim and many types of bivalves can burrow, most bivalves are primarily sessile (non-moving on the ocean bottom). So for many bivalves, the primary method they use to colonize new territories is to release planktotrophic (“plankton-eating”) larvae, which can be carried to new places by currents and feed on other plankton surrounding them. Many bivalves have broad distributions because of their ability to hitchhike on ocean currents when they are microscopic. They don’t even pack a lunch, instead eating whatever other plankton is around them. But once they settle to grow, they are typically fixed in place.

Not all bivalves have a planktotrophic larval stage, though. Larvae of lecithotrophic bivalve species (“yolk-eaters”) have yolk-filled eggs which provide them with a package of nutrition to help them along to adulthood. Others are brooders, meaning that rather than releasing eggs and sperm into the water column to fertilize externally, they instead internally develop the embryos of their young to release to the local area when they are more fully developed. This strategy has some benefits. Brooders invest more energy into the success of their offspring and therefore may exhibit a higher survival rate than other bivalves that release their young as plankton to be carried by the sea-winds. This is analogous to the benefits that K-strategist vertebrate animals like elephants have compared to r-strategist mice: each baby is more work, and more risky, but is more likely to survive to carry your genes to the next generation.

Brooding is particularly useful at high latitudes, where the supply of phytoplankton that is the staple food of most planktrophic bivalve larvae is seasonal and may limit their ability to survive in large numbers. But most of these brooding bivalves stay comparatively local compared to their planktonic brethren. Their gene flow is lower on average as a result, with greater diversity in genetic makeup between populations of different regions. And generally, their species ranges are more constricted as a result of their limited ability to distribute themselves.

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A bunch of G. trapesina attached to kelp. Notice the hitchhiking clams have in turn had hitchhiking barnacles attach to them. Freeloaders on freeloaders! Source: Eleonora Puccinelli

But some brooding bivalves have developed a tool to have it all: they nurture their young and colonize new territories by sailing the seas using kelp rafts. The clam Gaimardia trapesina has evolved to attach itself to giant kelp using long, stringy, elastic byssal threads and a sticky foot which helps it hold on for dear life. The kelp floats with the help of gas-filled pneumatocysts, and grows in the surge zone where it often is ripped apart or dislodged by the waves to be carried away by the tides and currents. This means that if the clam can persist through that wave-tossed interval to make it into the current, it can be carried far away. Though they are brooders, they are distributed across a broad circumpolar swathe of the Southern Ocean through the help of their their rafting ability. They nurture their embryos on specialized filaments in their bodies and release them to coat the surfaces of their small floating kelp worlds. The Southern Ocean is continuously swirling around the pole due to the dominance of the Antarctic Circumpolar Current, which serves as a constant conveyor belt transporting G. trapesina across the southern seas. So while G. trapesina live packed in on small rafts, they can travel to faraway coastlines using this skill.

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The broad circumpolar distribution of G. trapesina. Source: Sealifebase

The biology of G. trapesina was described in greater detail in a recent paper from a team of South African researchers led by Dr. Eleonora Puccinelli, who found that the clams have evolved to not bite the hands (kelp blades?) that feed them. Tests of the isotopic composition of the clams’ tissue shows that most of their diet is made up of detritus (loose suspended particles of organic matter) rather than kelp. If the clams ate the kelp, they would be destroying their rafts, but they are gifted with a continuous supply of new food floating by as they sail from coast to coast across the Antarctic and South American shores. But they can’t be picky when they’re floating in the open sea, and instead eat whatever decaying matter they encounter.

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Falkland Islands stamp featuring G. trapesina. Source.

The clams are small, around 1 cm in size, to reduce drag and allow for greater populations to share the same limited space of kelp. Their long, thin byssal threads regrow quickly if they are torn, which is a useful skill when their home is constantly being torn by waves and scavengers. Unlike other bivalves, their shells are thin and fragile and they do not really “clam up” their shells when handled. They prioritize most of their energy into reproduction and staying stuck to their rafts, and surrender to the predators that may eat them. There are many species that rely on G. trapesina as a food source at sea, particularly traveling seabirds, which descend to pick them off of kelp floating far from land. In that way, these sailing clams serve as an important piece of the food chain in the southernmost seas of our planet, providing an energy source for birds during their migrations to and from the shores of the Southern continents.

 

A to-do list: 239 ways (and counting) that Trump has hurt the environment. Let’s fight back!

I’ve had a hobby for the last couple months. I just finished my PhD in Earth Science, but on the side I’ve been making a to-do list. For the last two years, I’ve been watching the ways that President Trump is attacking the environment I study and my colleagues that study the environment. It was becoming difficult to keep track of all the ways that his policies have hurt the planet, so I started a list of things he’s done, with dates, sources, and agencies responsible included. As environmental voters, need need to cross items off this list as soon as we can.

I have categorized 120 actions as “ugly.” These are malevolent actions which I, an environmental professional, conclude will cause permanent damage to our planet’s lifeforms, both human and non-human. Some ugly actions are intended to purge the government of environmental professionals and scientists who cannot be easily brought back when Trump is gone. Their loss will take decades to undo.

119 actions are classified as “bad.” These are actions we can likely reverse when we vote in representatives who are responsible stewards of the environment. Unfortunately, Trump’s administration has likely moved the window of what was acceptable to Republicans in terms of environmental damage. I am worried that this is the new normal if we as voters to not register our displeasure.

12 actions are “neutral,” with implications that are unclear.

A sadly small 22 actions of the Trump administration can be classified as helpful to the environment. I am happy to add more if they are pointed out. These are glimmers of hope to me. They are a sign that some aspects of the machinery protecting our environment are still working despite attempts from Andrew Wheeler, Ryan Zinke, Scott Pruitt, Rick Perry and others who seek to permanently lobotomize the government’s ability to regulate harm against the environment.

I would note I probably would have several dozen more entries on this list if I included Mick Mulvaney’s proposed budgets here. Every year, he basically proposes firing all environmental scientists from the government and defunding most of the means we have to regulate pollution from corporations. So far, Congress has resisted 99% of his crazy proposals, but talking heads on Fox News and other conservative commentators have become increasingly vocal that they will not tolerate a budget next year which doesn’t include significant cuts to research and environmental protection. So next year, we may witness irreplaceable programs get put on the chopping block. Researchers may get laid off. And these educated professionals will leave the work force never to return if that happens.

I believe that as a whole, this list represents a crime against our world by an administration that was not elected with a popular mandate. The voters who elected them will be hurt by many of these actions. As soon as we have the means to, environmentally conscious voters must begin pressuring our representatives to undo these crimes against the planet. Our children are depending on us to reconstruct the mechanisms needed to rein in pollution, stop climate change and study humanity’s place in the environment. I will be keeping this list in mind when I vote in the future, so I thought I’d share it and update it. Please feel free to comment with any items I may have missed and I will update the spreadsheet.

Weird Clam Profile: Pinna nobilis

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A fan mussel among the seagrass it calls home (Arnaud Abadie on Flickr)

The fan mussels (Pinna nobilis) are a species of enormous mussel which live in seagrass beds of the Mediterranean Sea. They can grow to nearly 4 feet long (though most are 1-2 feet in size at maturity), and live with most of their bodies protruding straight up out of the sediment, anchored down into the sand with long rootlike byssal threads which grow out of their rear hinge.

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They are really enormous (Marc Arenas Camps on WordPress)

These mussels grow up to 20 cm per year, almost entirely in the vertical direction. As they gain in mass, their bodies start to sink in the sand beneath them, so it is believed this extremely fast growth rate evolved in order to stay above the sediment. It also helps them to remain elevated above the seagrass around them, where they can access passing phytoplankton and organic particles in the current.

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A sea silk glove (Wikipedia)
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Close up view of the hairlike byssus. I definitely am feeling some beard envy here. (Wikipedia)

Because they are exposed to the current like a giant fan, they need a very strong anchor. So they create huge quantities of byssal threads which root them down in the sand. These byssal threads are known as as “sea silk” and communities around the Mediterranean have used the silk to sew clothing for thousands of years. The material is extremely fine but strong, and has historically been of immense value as a result. Sea silk or sea wool is mentioned in writings of the ancient Egyptians, Greeks and Romans.

Unfortunately, the fan mussels are considered critically endangered due to overharvesting, pollution, climate change and destruction of their native seagrass habitats. However, they are now protected and active conservation efforts are underway. When the cruise ship Costa Concordia ran aground off of Italy in 2012, a community of fan mussels were rescued from a seagrass bed next to the wreck and moved to another nearby site. I hope someday to study the fan mussels because I find them to be a truly charismatic bivalve with many interesting mysteries still waiting to be uncovered about their unique lifestyle.

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Huge pen shell I saw at the Hebrew University Museum in Jerusalem. My lens cap is only 6 cm to give you a sense of scale! The shells are fragile and easily break.

Killer Clams

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Some shells of the carnivorous genus Cardiomya. Notice the protuberance off one side, making space for the overdeveloped siphon they use to capture prey (Machado et al. 2016)

You might think of clams as rather pacifistic creatures. Most of them are; the majority of bivalves are filter-feeding organisms that suck in seawater and eat the yummy stuff being carried by the currents. This mostly means phytoplankton, tiny single-celled photosynthetic plankton which make up most of the biomass in the world’s oceans. Most bivalves could be considered exclusively herbivorous, but as I’ve learned happens throughout evolutionary biology, there are exceptions to every rule. We already talked about parasitic bivalves that have evolved to hitch a ride on other hapless marine animals. But there is an even more sinister lineage of bivalves waiting in the sediment: yes, I’m talking about killer clams.

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View of the oversized siphon (Machado et al. 2016)

Carnivory in bivalves has evolved multiple times, but the majority of known carnivorous bivalves fall within an order called the Anomalodesmata. Within that order, two families of clams called the Poromyidae and Cuspariidae have a surprising number of species which are known to eat multicellular prey.

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Evil clams are also the star of my favorite Spongebob episode

Now, you can rest easy because there are no clams that eat people. You’re safe from the Class Bivalvia, as far as we know. But if you were a small crustacean like a copepod, isopod or ostracod, you would be quite concerned about the possibility of being eaten by a poromyid clam in certain regions of the world. These clams lie in wait in the sediment like a sarlacc, with sensory tentacles feeling for passing prey and a large, overdeveloped siphon ready to suck up or engulf their helpless targets.

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Until we catch the feeding behavior of poromyids on video, these whimsical artist’s depictions will have to do (Morton 1981).

Because they spend their lives under the sediment, these clams aren’t very well studied, and the first video of them alive was only taken in recent years. In addition, many of these killer clams live in deeper water, where their murderous lifestyle provides an advantage because food supplies can be much more sparse than in the sun-drenched shallow coastal zone. Much like the venus flytrap and carnivorous plants have arisen in response to the low nutrient supply of boggy swamp environments, the ability to eat alternative prey is valuable to the killer clams in all sorts of unconventional environments.

The siphon which these clams use to suck up their prey is a repurposed organ. In most other bivalves, the siphon is usually a snorkel-like organ which enables the clam to safely remain buried deep in the sediment and still breathe in oxgyen and food-rich water from open water above. But for the poromyids, the siphon is instead a weapon which can be used like a vaccum cleaner hose, or even be enlarged to engulf hapless prey. The poromyids have also evolved to have a much more complex, muscular stomach than any other bivalves. It takes a lot more energy to digest multicellular food, while most other bivalves simply just feed from the single-celled food they catch on their gills, expelling the other un-needed junk as “pseudofeces.”

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Dilemma, another strange carnivorous bivalve which eats marine isopods (pill bugs), found from deep waters off the the Florida Keys, Vanuatu and New Zealand (Leal 2008)

Hopefully soon we will have video of this predatory activity in action. But until then, you can imagine that somewhere on earth, tiny copepods foraging on the surface of the sediment pass by a strange field of squishy tentacles. Suddenly, out of nowhere a hellish giant vacuum hose appears in view and sucks them in like Jonah and the whale. Then it’s just darkness and stomach acid. What a way to go!

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Lyonsiella going after a doomed copepod (Morton 1984).

Weird Clam Profile: Hammer Oysters

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Malleus malleus from Indonesia. Source: Wikipedia

Oyster. Reading that word, you probably formed an image in your mind of a rough-shelled creature with a shiny mother-of-pearl (nacreous) inside that someone pulled out of some silt in an estuary. And yes, that’s what most oysters look like. Some oysters are of additional economic value through their creation of pearls. These pearl oysters have long, straight hinge lines and live in the tropics in and around coral reefs.

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A pearl oyster. See the straight hinge? Source: Pearl Paradise on Flickr

The hammer oysters are another sort of oyster, not of the Ostreidae family that includes most of the bivalves we think of as oysters, but still closely related and in its own family, the Malleidae. Malleus is the latin word for hammer, and the most distinctive genus of hammer oysters indeed look just like a hammer sitting on the seafloor.

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In a typical life position in a seagrass bed. Notice all the algae, anemones and other encrusting creatures freeloading off the hammer oyster’s hard work. Source: Ria Tan on EOL

What the…that thing’s alive? How does that even work? This is an oyster? That’s how I imagine the first scientist to discover the hammer oyster reacting. Because they are weird and rather incomprehensible-looking. But when you know the way they live, it makes more sense.

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There is a small area of nacre (mother of pearl) in the area near the rear of the interior. Source: Archerd Shell Collection

The hammerhead part of the oyster is just a super elongated hinge. The creature has a long, straight hinge like other oysters, but it has evolved to instead have a relatively narrow set of valves attached to that ridiculously overbuilt hinge. Like other oysters, they secrete byssal threads from their backside to attach themselves to the bottom. The narrow valves commonly poke up out of sandy bottoms in tropical waters nearby coral reefs. They do particularly well in seagrass beds, and often live in large colonies similar to other oysters.

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Shell collectors seek out hammer oyster shells which have other bivalves attached. Here is a thorny oyster living on top of Malleus. Two for one! Source

The absurd hinge helps these creatures to stay anchored into the sediment, but also serves as “wings” that help it avoid sinking into the sediment over time. One thing us humans don’t realize sitting on sand is that it actually acts like a liquid. Over time, if we sat on wet sand, we would likely begin to sink in unless we spread out our arms and legs to increase our surface area. In the ocean, all sand is quicksand. Different organisms have different strategies to avoid being engulfed by the sediment they live on, and the hammer oyster has had good success with its strategy. It doesn’t care that you think it looks weird. It just sits there, filtering water for passing food particles and plankton. It’s very good at it, has been perfecting the strategy for over 250 million years, and doesn’t need your smartass remarks, thank you very much.

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Another shot of a happy hammer oyster doing what it does best, in a seagrass bed near Singapore. Source: Wild Singapore on iNaturalist

The boring giant clam is anything but.

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Tridacna crocea, bored into a coral head on a reef in Palau

There are many types of giant clam. Not all of them are giant; the boring giant clam, Tridacna crocea, only grows to 10 cm long or so. The boring giant clam is not so named because it’s dull; its main skill is its ability to bore into the coral of its coral reef home and live with its entire shell and body embedded in the living coral. They sit there with their colorful mantle edge exposed from a thin opening in the coral, harvesting energy from sunlight like the other giant clams. When disturbed by the shadow of a human or other such predator, they retract their mantle and close their shell, encased by an additional wall of coral skeleton. It’s a clever defensive strategy, and they are some of the most numerous giant clams in many reefs in the Eastern and Southern Equatorial Pacific.

But it’s always been a mystery of how they bore away at the coral so efficiently, and how they continue to enlarge their home as they grow their shell. There are other bivalves that are efficient borers, including the pholad clams (“piddocks”) which use sharp teeth on their hinge to carve their way into solid rock, and the shipworms, which have abandoned their protective shell and instead use their two valves as teeth to burrow into wood. Both of these methods of boring are pretty straightforward.

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Piddocks in next to holes that they made in solid rock. Source: Aphotomarine

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Shipworm embedded in wood. Source: Michigan Science Art via Animal Diversity Web

But the boring giant clam has no such adaptation. It does not have large teeth on its hinge to carve at the coral. Such abrasion of the coral would also not explain how they widen the opening of their cubby-holes to allow their shell to grow wider. This mystery has long confounded giant clam researchers. I myself have wondered about it, and was surprised to find there was no good answer in the literature about it. But now, a team of scientists may have cracked the problem once and for all.

At the back of T. crocea‘s shell at the hinge, there is a large “byssal opening” with a fleshy foot which they can extend out of the opening to attach themselves to surfaces. Giant clams that don’t embed in coral (“epifaunal,” resting on the surface of the coral rather than “infaunal,” buried in the coral) lack this opening. The researchers suspected that the foot was the drilling instrument the clam used to create its home.

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Byssal opening of T. crocea with the foot retracted. Source: NickB on Southwest Florida Marine Aquarium Society

How could a soft fleshy foot drill into the solid calcium carbonate (CaCO3) skeleton of corals? I can confirm from experience that my own foot makes for a very ineffective drilling instrument in such a setting. But T. crocea has a secret weapon: the power of acid-base chemistry. CaCO3 can be dissolved by acids. You may well have taken advantage of this chemistry to settle your acid stomach by taking a Tums, which is made of CaCO3 and reacts with the excessive hydrochloric acid in your stomach, leaving your tummy with a more neutral pH. pH is a scale used to measure acidity, with low numbers indicating very acidic solutions like lemon juice, and high pH indicating a basic solution like bleach.

Scientists are well aware of the hazards corals face from decreasing pH (increasing acidity) in the oceans. All the CO2 we are emitting, in addition to being a greenhouse gas, dissolves in the ocean as carbonic acid and gets to work reacting and dissolving away the skeletons of corals and any other “calcifying” organisms that make shells. It makes it harder for corals to form their skeletons and is already worsening die-offs of corals in some areas. The researchers suspected that the clams use this phenomena to their advantage at a small scale, lowering the pH with their foot somehow to dissolve away the coral to make their borehole.

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Using a wedge to keep open a Tridacna shell in my Red Sea work. We took a small blood sample with permission of local authorities. This caused no lasting effects to the clams.

But they needed to prove it, and that was a challenge. Giant clams can be unwilling research participants. I myself have observed this in trying to take samples of their body fluid for my own research. When they sense the presence of a predator, they immediately clam up in their protective shell. I used a small wedge to keep their shells open to allow me to take a sample of their body fluid, but the researchers working on T. crocea needed to convince the clam to place its foot on a piece of pH-sensitive foil, keep it there and do whatever acid-secreting magic allows it to burrow into coral. They would then be able to measure whether it indeed is making the water around its foot more acidic, and by how much.

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Diagram from Hill et al., 2018 showing their experimental design.

In what I can only assume was an extended process of trial and error and negotiation with a somewhat unwilling research subject, the researchers found exactly the right angle needed to convince the clam that it was safe enough to try making a coral home. But it was not in coral, instead sitting in an aquarium, on top of a special type of foil that changes color when exposed to changing pH, like a piece of high-tech litmus paper. The researchers discovered that their suspicions were correct: the clams do make the area around their feet significantly more acidic than the surrounding seawater, as much as two to four pH units lower. Where seawater is around a pH of around 8, the clams were regularly reducing pH to as low as 6 (about the level of milk) and sometimes as low as 4.6 (about the pH of acid rain). Small differences in pH can make a big difference in the power of an acid because each pH unit corresponds to 10x more protons (hydrogen ions, H+) in the water. The protons are the agent that dissolves CaCO3. Each proton can take out one molecule of coral skeleton. The clams are dissolving away coral skeleton to make holes with only their feet!

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Footage of the pH- sensitive foil, with darker areas corresponding to lower pH. The areas of low pH (high acidity) correspond exactly to the “footprint” of the clam!

But what in T. crocea‘s foot allows them to make acid? I know that my foot does not do this, though that would be a very entertaining and obscure superpower. The researchers found the enzymes called vacuolar-type H+-ATPase (VHA) present in great quantities in the outermost cells of the clam’s feet. These enzymes are found throughout the tree of life and are proton pumps that can quickly reduce pH through active effort. Other prior researchers like the influential Sir Maurice Yonge, a legendary British marine biologist who worked extensively with giant clams, had suspected that the clams had used acid but had never been able to detect a change in pH in the seawater around the clams’ feet through more conventional methods. It was only because of new technologies like the pH paper that this research team was able to finally solve this issue. And now, I suspect other groups will want to re-investigate the importance of VHA in their study organisms. Many branches of the tree of life may be utilizing acid-base chemistry to their advantage in ways we never had previously imagined.

Weird Clam Profile: The Heart Cockles

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Corculum cardissa (from Wikipedia)

The heart cockle (Corculum cardissa) is so named because of its heart shaped shell. It is native to warm equatorial waters of the Indo-Pacific. While many bivalves sit with the their ventral valve facing down, the heart cockle sits on its side, with one side of both valves facing downward. The valves have adapted to resemble wings and are flat on the bottom, providing surface area that allows the bivalve to “raft” on the surface of soft sandy sediment and not sink. They may also sit embedded in little heart-shaped holes on the tops of corals.

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Two heart cockles embedded in the top of a Porites coral. Source: Reefbuilders
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A particularly green heart cockle from Singapore. Source: orientexpress on iNaturalist

Heart cockles are a member of a small club of bivalves which partner with symbiotic algae for nutrition created by photosynthesis. Most of the modern photosymbiotic bivalves are in the family Cardiidae, the cockles. The giant clams (Tridacninae) are also in this family and have a similar partnership with the same genus of Symbiodinium algae. This algae is also found in many species of coral.

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The dark circles in these microscope images are Symbiodinium. The top is a view of giant clam body tissue. The cells are present throughout the tissue in giant clams. The bottom shows heart cockle “tubules” which contain their symbiotic algae. The algae are restricted to narrow tubes that run through the tissue of the cockle. Source: Farmer et al. 2001

So when you find a live heart cockle, it is often green in color, because of the presence of this algae near the surface of its tissue. Its shell has adapted to be “windowed” (semi-transparent) to allow in light for the algae to harness to make sugars. The algae are housed in networks of tubes within the soft tissue of the cockle. They trade sugars with their host in exchange for nitrogen and carbon from the clam.

As I’ve mentioned before regarding the giant clams, this is a very productive partnership and has evolved separately several times in the history of bivalves. However, we don’t know why almost all examples of modern bivalve photosymbiosis occur in the cockles. Why aren’t the heart cockles giant like the giant clams? What features are necessary to allow this symbiosis to develop? These are the kind of questions I hope to help answer in my next few years of work.

Oh, the seasons they grow! [research blog]

My latest clamuscript is published in Palaios, coauthored with my advisor Matthew Clapham! It’s the first chapter of my PhD thesis, and it’s titled “Identifying the Ticks of Bivalve Shell Clocks: Seasonal Growth in Relation to Temperature and Food Supply.” I thought I’d write a quick post describing why I tackled this project, what I did, what I found out, and what I think it means! Raw unformatted PDF of it here on my publication page.

Why I did this project:

I study the growth bands of bivalve (“clam”) shells. Bivalves create light and dark shell growth bands as they grow their shells, much like the rings of a tree. The light bands form during happy times for the clam, when it is growing quickly and putting down lots of carbonate. The dark bands appear during times of cessation, when the bivalve ceases growth during a hibernation-like period. This can happen in the cold months, or the hot months, or both, or neither, depending on the clam and where it lives. It turns out that there are a lot of potential explanations for why these annual cessations of growth happen. Different researchers have suggested through the years that temperature (high or low) is the biggest control on the seasons that bivalves grow, but others have suggested that food supply is more important. Others say it’s mostly a function of the season they reproduce, when they’re putting most of their energy into making sperm/eggs and not growing their bodies. I wanted to try to see if I could find trends across all of bivalves which would shed light on which factors are important in determining their season of growth.

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Annual growth lines in the shell of a giant clam. The transparent spots are the times that it was growing more slowly and not happy. Was this because of temperatures? Or was it getting less to eat? I wanted to know.

What I did:

I read a ton of papers in the historical literature about bivalves. These were written by people in many fields: aquaculture, marine ecology, paleoclimate researchers (using the clams shells as a chemical record of temperature), and more. All of the papers were united by describing the seasons that the bivalves grew, and the seasons that they stopped growing. I ended up with nearly 300 observations of marine (saltwater) bivalve growth for dozens of species from all around the world. I had papers as old as the earliest 1910s, and some as new as last year.

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A map of all the places the observation of bivalve growth came from. Blue means they shut down in the winter, while red means they do not.

We have mussels, oysters, scallops, clams, cockles, geoducks, giant clams, razor clams, quahogs, and more in the database. Bivalves that burrow. Bivalves that sit on the surface of the sediment. Bivalves that stick onto rocks. Bivalves that can swim. With each, I noted data that the researchers recorded. If they grew during a season, I coded it as a 1. If they didn’t, I coded it as a 0. So a bivalve growing in summer but not winter would be recorded as 1,0. I also recorded environmental data including temperature of the location in winter and summer in the location, as well as seasonal supply of chlorophyll (a measure of phytoplankton, which is the main source of food for most clams). It turned out that not enough of the studies recorded temperature or chlorophyll for their sites, so I wanted to back these up with an additional data source. I downloaded satellite-based temperature and chlorophyll data for each location, as well as additional studies which directly measured chlorophyll at each site. I wanted lots of redundant environmental data to ensure that any trend or lack of trend I observed in my analysis was not due to a weakness of the data.

I then compared the occurrence of shutdown by season with these environmental variables using a statistical technique called regression. Regression basically involves trying to relate a predictor variable (in this case, latitude, temperature and chlorophyll during a certain season) to the response variable (did the clam grow in that season or not?). We wanted to see which environmental variable relates most closely to whether or not the clam grows or not. Because our dependent variable was binary (0 or 1), we used a technique called logistic regression, which tries to model the “log odds” of an event occurring in response to the predictor variable. That log odds can then be back-calculated to probability of the event occurring.

What we found:

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In a clamshell, we found that latitude (distance from the equator) is a very good predictor of whether or not a bivalve shuts down for the winter. As you’d expect, bivalves in the far north and far south of our planet are more likely to take a winter nap. However, bivalves at the equator mostly grow year round and are not likely to take a summer nap. In relation to temperature, the lower the winter temperature, the more likely the bivalve is to stop shell growth. High summer temperature is not as good a predictor for the occurrence of a summer shutdown, but the majority of summer shutdowns seem to occur at the low temperate latitudes, where the difference between the annual range of temperature is largest. Unlike at the equator, where bivalves likely can adapt to the hottest temperatures and be happy clams, they have to adapt to a huge range of temperatures in places like the American Gulf and Atlantic coasts, the Adriatic and Gulf of California. And if they are restricted at the northward end of their range, they may have no choice but to shut down in summer as there is nowhere cooler to migrate to.

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GIF of the satellite data showing white as hotspots of phytoplankton ability. Notice that the food is more available in summer months for each hemisphere. We were trying to see if this relates back to when the bivalves grow in every place we had data for.

Food supply, on the other hand, is not a good predictor of when bivalves shut down. When we went into this project, we expected food to be a powerful control on seasonal growth because it is intuitive and well understood that the better fed a bivalve is, the larger it will grow overall. But the seasonal low amount of chlorophyll (and therefore the amount of photosynthesizing plankton) in the bivalves’ areas had no relationship to whether or not the bivalve shut down in a certain season. To double check that this wasn’t a weakness in my satellite data, I downloaded additional direct observations from the same places as many bivalve studies in the dataset, but I still couldn’t find the relationship. We propose that the seasonal supply of phytoplankton is not well related to seasonal growth of bivalves because: 1) phytoplankton supply isn’t very seasonal in nature in most of the sites we studied. There are peaks in multiple seasons rather than a clean up and down wave shape like temperature. 2) Bivalves are pretty flexible in what they eat. They also eat other types of plankton and suspended particles that are even less seasonal. It may be pretty difficult to find bivalves that are seasonally starving. One of the most probable places to find such starvation shutdowns might be the poles, where seasonal ranges of temperature are quite small but plankton does really have a seasonal pattern of availability. More research will be needed to describe the nature of polar bivalves and why they shut down growth.

What’s next?
This is the first chapter of my PhD. I have two more chapters I’m working on, both related to the geochemistry of bivalve shells. I am writing those manuscripts this summer and looking for postdoctoral fellowships in the fall related to geochemistry of marine organisms in the fossil record. I hope to pursue more projects looking at the season of growth in bivalves, switching to understanding the role that changing seasonal cycles in their environment and biology play in their evolution. Do bivalves that live closer together tend to reproduce at different times? Can we track season of reproduction in relation to temperature and food supply? There are a lot more clam stories to be told and I look forward to sharing them all with you. Until the next research blog,

Dan