I used to have pride in being American. I’m grateful for all the opportunities and privileges I’ve had being a citizen of this storied democracy. I held onto hope when my countrymen doubted the citizenship of my president. I held on when we elected a fraudulent, undignified xenophobe to succeed him. I held on when we left a climate agreement out of spite and began rolling back environmental protections left and right. But today, I don’t know if I can do it. I don’t really feel like part of this place anymore.
I’m still trying to figure out my career. If I stay here after grad school, I’ll be a more inward looking person; thinking about my own life, friends and family. But I’m looking into leaving. I don’t really feel like I can be part of this shared enterprise anymore. It’s really out of exhaustion more than anger. I’m tired of this feeling of grief. It’s analogous to the feeling I’d have after losing a loved one, when I just want to disconnect. The country I grew up in is no more, and it may be time to move on.
Humans aren’t the only users of fossil fuels. In many parts of the ocean, natural gas (methane) is constantly bubbling out of the sediment. These areas are known as cold seeps and are often a marker of productive fossil fuel reservoirs in the crust underneath. The name cold seep is somewhat of a misnomer (they are often slightly warmer than surrounding waters), but they are indeed much cooler than the more famous hydrothermal vents, which form due to geothermal activity. They are often found in shallower waters than hydrothermal vents, which generally occur in the deepest regions of the ocean where the earth’s crust is rifting. As with hydrothermal vents, cold seeps provide a unique opportunity for ecosystems to arise which are based on chemical energy, rather than solar-powered photosynthesis like the rest of the biosphere. Unusual life forms harness the chemical energy of the methane and sulfide emitted at these seeps, and many can also be found at the more famous hydrothermal vents.
Crabs feeding on a bed of Bathymodiolus. Source: NOAA
Bathymodiolus mussels, vesicomyid clams, and other bivalves thrive at these seep environments, and have evolved to partner with bacteria in their gills and stomachs which can directly consume and produce energy from the reaction of methane and sulfate continuously being sourced from the seep underneath, creating bicarbonate and sulfide as products. This form of metabolism, chemosynthesis, is distinct from the familiar photosynthesis/respiration that most life-forms at the surface use to create energy. The partnership between a multicellular animal and chemosynthetic bacteria is called chemosymbiosis. These reactions are of course being utilized by all sorts of microbes not partnering with bivalves, but the bacteria that take on metazoan hosts have the advantage of a stable environment and a constant flow of fresh seep gas brought in by the bivalves’ gills. The bivalves feed on the products of the microbe’s hard work. As they are some of the only inhabitants that can tolerate the oxygen-free, toxic environment of seeps, they form dense thick shell beds wherever a seep appears.
Other chemosymbiotic groups use the hydrogen sulfide byproducts from seeps, which they oxidize into elemental sulfur. The most prominent of these are the vestimentiferan tubeworms, which lack mouth or anus and are totally dependent on the activity of the bacteria that they house in a modified digestive tract. Some of these worms have been found in seeps in extreme environments, such as the truly cold cold seeps of the Arctic. They are less spectacular in appearance than their bright red counterparts from hydrothermal vents, but are believed to live for an extremely long time, depending on the consistency of the seep that they inhabit.
At the extreme pressures and low temperatures of the deep ocean, methane can freeze in combination with water molecules, forming structures called clathrates. Much of the deep ocean floor is dusted with deposits of clathrates. Microbes which feed on clathrates are believed to be a food source for grazing polychaete “ice worms.” These unusual organisms can survive up to 96 hours without a whiff of oxygen, an unbelievable feat for a moving, multicellular organism.
Cold seep environments are perhaps merely one specific manifestation of a vast, poorly understood collection of biota which do not depend on the sun for their energy. We do not yet understand many of the deep ecosystems which may be present within the earth’s crust, in the deep ocean and trapped under polar ice. NASA studies cold seep and hydrothermal environments as the best analog for the conditions life could experience in the frozen oceans of Europa and Enceladus. It is eerie to think that such alien ecosystems exist merely a few kilometers off of our familiar shores, and were using fossil fuel energy far before humans figured out how to combust it.
Bivalves put a lot of energy into their shells. These hardened, hinged sheaths of carbonate are an effective defense against many predators looking to get at the squishy clam’s body encased inside. Parasitic pea crabs have evolved to free-ride on the bivalves’ hard work.
(video courtesy Dana Shultz)
Pea crabs are small (pea-sized), very specialized parasites which live in the mantle cavity of many bivalve groups including oysters, mussels, clams and more. The mantle is the wall encasing the soft body of the bivalve, and the cavity is the space between this soft gooey tissue and the shell itself.
For a pea crab, there is no better place to be than this tiny, claustrophobic space. In fact, they can’t live anywhere else, though some species have been found in other unusual places such as inside the anuses and respiratory tracts of sea cucumbers (link SFW, fortunately, unless you’re a sea cucumber). In a bivalve host, the crab is protected from predation by the shell, and the bivalve provides a constant buffet of food as it sucks in suspended particles with its gills. The crab steals some of this food from itself before the bivalve can digest it.
As you might imagine, having a crab living in you taking your food and pinching at your gills is not an ideal arrangement for the bivalve. Pea crabs damage their hosts’ gills with their constant picking, and bivalves infected with crabs suffer slower growth than uninfected individuals, particularly for those unlucky enough to play host to the larger female pea crabs. At a certain point, the males will sneak out of their hosts and find a bivalve with a female crab inside. At this point, they mate inside the host’s shell, adding great insult to injury. The female releases her larvae, which swim out to infect new hapless bivalves and start the cycle over again.
You might think that commercial oysters with crab parasites would be thrown out, but to the contrary, finding a pea crab or its close relative the oyster crab with your meal is a cause for celebration in some areas, such as the Cheasapeake Bay. The crabs are eaten whole and often raw, and are said to have a texture akin to shrimp, with notes of sweetness and umami. Personally I prefer surprises in my Kinder eggs rather than in my shellfish, but to each their own.
Hermit crabs (superfamily Paguroidea) are most famous for using snail shells as their home, having evolved a soft, spiral abdomen to be able to use them for protection. But they are more flexible about their choice of abode than you might expect.
Different groups of shelled organisms have risen and fallen in abundance through geological time. During the time of the dinosaurs, ammonites (relatives of modern squid and octopus) were among the most common marine organisms, and hermit crabs were there to recycle their shells when they died.
Mollusks aren’t the only contractors for hermit crabs. Some hermits utilize the skeletons of colonial organisms like bryozoans as a home. Bryozoans are filter-feeding colonial animals made up of thousands of tiny tentacled organisms living in the pores of a shared skeleton. The extinct bryozoan Hippoporidra lived in symbiotic partnership with hermit crabs, growing around a gastropod shell to attract a hermit crab partner. This was an example of mutualism: by providing a home for a crab, the bryozoan would be transported to new environments with plentiful food particles to eat, and also would be protected from their arch-enemy, nudibranchs (sea slugs). Some modern day hermits, such as Manucomplanus varians of the Gulf of California, have evolved very similar partnerships with live staghorn corals.
Not all hermit crabs live in hard houses. Some deep sea forms partner with anemones, with the stinging tentacles serving as an effective defense.
The recently discovered green-eyed hermit crab, which also lives in deep water, lives in a glued-together mass of sand created by tiny anemones, which continue to grow the structure to fit the crab as it increases in size.
Unfortunately, hermits adapted for gastropod shells are unable to find adequate homes in some areas, due to overharvesting of shells for the tourist trade as well as an excess of plastic trash. These crabs make do with whatever items that they can find. Plastic is not an ideal home material for hermits. Bottlecaps and narrow tubes do not allow the crab to fully retract for protection and leach chemicals which may harm the crab. The crabs also nibble on their shells as a source of calcium, which is obviously not possible with plastic.
But hermits continue to impress me with their flexibility and ingenuity in their search for homes. For a hermit crab, home is where the abdomen is.
Agave americana, the century plant. If we cut this stalk before it flowered, we could harvest the sweet liquid that would come out, ferment it, distill it and make mezcal. Personally I prefer the flower.
Biologists have long wondered at the capabilities of earthworms. When he wasn’t crafting foundational theories of modern biology, Charles Darwin discovered that earthworms assist plant growth by aerating and turning over soil. Previously derided as pests, his work helped to shed light on the dark, dirty, essential role of these silent tillers of the earth. Earthworms spend most of their lives converting organic matter into compost. They play an important role in nutrient cycling, as the castings that they leave behind are rich in important nutrients like phosphorus and calcium.
Our sunny, dry surface world is not safe for these subterranean beasts. Earthworms are not at home in daylight and are usually only there by necessity. One of the most common times to observe them is during and after a rainstorm, particularly at night. As a child, I often wondered why earthworms seemed so determined to drown themselves in puddles. Researchers have still not reached consensus on the causes for this behavior. Darwin supposed that the sicker worms were driven to the surface by flooded soil. Some propose that they are driven from the saturated soil by low oxygen content, where many drown in puddles as they attempt to find non-waterlogged soil. Other researchers are skeptical of this angle, as worms require moisture to breathe through their skin, and many species can survive immersion in water for extended periods. They suggest that the worms are using the wet conditions brought by rains to aid migration to new patches of soil, or even to mate. The reality, as often is the case, is likely something of a combination of all of the above.
One team found that different earthworm species have different tolerance levels for low oxygen conditions. The worms that can survive extended periods of immersion in water are the same species that often remains under the ground following a rainstorm. These worms have lower oxygen consumption. The worms with higher rates of oxygen consumption leave the ground when dissolved oxygen levels are too low to sustain respiration. They do so preferentially at night, partially because this is a period when they are more active, and thus respiring more oxygen, and also because at night they are less exposed to predation by birds. The early bird (at least before sunrise) really does tend to get the worm.
Some have suggested that the rhythm of raindrops stimulates the emergence of earthworms, and that the same mechanism allows fishermen (and animals) to use “worm fiddling” or charming to gather thousands of worms at a time for bait. Worm fiddling can take many forms, but one of the most common techniques observed involves rubbing a long piece of metal against a post driven into the ground. The vibrations induce thousands of worms to rise up out of their burrows.
Ken Catania, a biologist at Vanderbilt University, rejected the rain rhythm idea and proposed that worm fiddling actually works by imitating the noise of a burrowing mole, one of the most ravenous predators of worms. Rather than fleeing from the simulated rain, the worms are fleeing the jaws of their greatest enemy, only to be trapped at the surface by a different adversary. Like a whale driven to beach itself by noise pollution or the threat of a predator, surfaced earthworms deserve our sympathy, particularly if they’re destined to become our fishing bait.
As I branch out and prepare the first articles I’ve worked on in a while, I thought I’d set up a new home base to host my writing and contact information. So keep an eye out for posts about all sorts of topics, including my research and my numerous interests.