A Clam for Ken Kesey

"That's a CLAM!?" This reaction to a particular animal is almost guaranteed when people look at them for the first time. Check it out.

Oh man, who just leaves a tie-dye shirt laying around on a coral reef?
Courtesy: Nick Hobgood via Flickr

Okay first off, that looks nothing like what belongs in my chowder. Second, this animal just goes to prove that the 60's got to everyone. So where does counter-culture clam come from and why's it so psychedelic? Editor's Note: This post is greatly improved when accompanied by Strawberry Alarm Clock's: Incense and Peppermints, or your own favorite psychedelic rock song.

Well what you're looking at is a Tridacna (pronounced: Tri-dack-na) clam. They're more commonly called giant clams, but I don't really like that name because not all of them are giant. In fact one species, Tridacna maxima, has the common name "small giant clam"; that's just silly so were gonna stick with their scientific name for this post. Anyway Tridacna don't look much like their relatives, but all the pieces are still there. They have heavy rippled shells like their cousins the cockles, and the part that you see sticking out is their mantle (the body of a mollusk) and their siphons (The channels clams use to feed and breathe). These combined anatomical parts are what make up the "meat" of the clam that we eat.

Plankton filled water flows into the hole on the right, and strained 
water flows out of the tube on the left.
Courtesy edgeplot via Flickr

Tridacna clams live on coral reefs in the tropical Western Pacific. Once they settle out from the plankton they spend their entire lives in that single spot. They don't dig into the ground, but instead let it all hang out. Truly these bivalves (animals with two shells) have gotten the hippy lifestyle down pat.

In fact it turns out that Tridacna's trippy colors and patterns are essential to its survival. The reason Tridacna don't dig into the sand is that they're part of a self sustaining commune. Just like the stony corals around them; these mollusks host symbiotic algae under their skin. In order for the algae to photosynthesize they need to be exposed to the sun. The hinge of the clam's shell is heavier than the opening, so it can tilt face up and spend the daylight hours with its skin spread out in the light. The algae get protection from consumers, and the clam gets nutrients without having to feed. Having a backup way to get your food is especially helpful on coral reefs because the water around them is usually lacking in plankton. Completely clear water is great for snorklers' ability to see, but not so great for filter feeders' ability to eat.

"Come on baby light my zooxanthellae" -Jim Molluskson
Courtesy: Eric Johnson via the NOAA Photo Library

Now as anyone who's forgotten sun screen on a tropical vacation can attest, the sun at the equator is incredibly strong. Solar radiation in the middle of the day is so intense that photosynthesis can actually decrease as the clam's symbiotic algae try to protect themselves from sun burn. But this is a collective man, and the clam does its part to help the algae function efficiently.

The algal cells under the clam's skin are arranged in stacked towers, which is confusing because that means the cells on top shade out those below them. To counter this Tridacna have their own cool cells called iridiocytes (pronounced: ear-id-ee-oh-sites) which bend light in different directions. The iridiocytes reflect yellow and green light (which aren't used by the algae) away from the stacks, and reflect blue and red light (which are useful) towards them. Essentially the iridiocytes screen out the best light for the algae, soften its intensity, and evenly distribute it across the stacks of cells.

The combination of colorful algae and reflected light come together to create the mind expanding visual experience of looking at a Tridacna's skin. Cameras can't really capture how magnificently colored these animals are, so I really encourage you all to take a trip to your local aquarium and see them for yourselves. But here's another picture to tide you over 'til then.

  Couretsy: Nick Hobgood via Flickr

References:

Holt et al., "Photsymbiotic giant clams are transformers of solar flux", Journal of the Royal Society Interface, Oct. 2014, DOI 10.1098/rsif.2014.0678 Accessed via:

http://rsif.royalsocietypublishing.org/content/11/101/20140678 

Soo, Pamela & Todd, Peter A., "The behaviour of giant clams (Bivalvia: Cardiidae: Tridacninae)", Marine Biology, 2014, DOI 10.1007/s00227-014-2545-0 Accessed via:

http://link.springer.com/article/10.1007/s00227-014-2545-0/fulltext.html

Life, uh, Finds a Way

A few hundred years ago we believed that nothing could live in the deep sea. Even as our understanding of the world grew, in some ways we lost our imagination. We began to understand that the deep was incredibly cold, very low in oxygen, and subject to astonishing pressures. So we assumed that this environment was just too inhospitable . Boy were we ever wrong.

A mile and a half down (2560m), on the vent field of an active volcano.
Courtesy NOAA Ocean Explorer via Flickr

More and more, we're seeing that life not only exists in the darkness, but thrives. A few weeks ago we talked about animals up in the water that survive with little light, but now we're headed to the bottom. The above image comes from a deep sea hydrothermal vent community, which in the last few years has become relatively well known. Thanks to programs like Blue Planet and Planet Earth, there is beautiful footage of these ecosystems readily available to the public.

But hydrothermal vents are a small part of the ocean bottom. Other incredibly diverse ecosystems exist, and with the prevalence of the internet, researchers are starting to show them as they're discovered. Some of the coolest environments being found are cold seeps.

There are several types of cold seep ecosystems, but what defines them all, is gasses escaping from underground into the water. Seeps have been found all over the world, from as shallow as 15m (easily diveable) to over 7000m (not easily anything), and even in inland bodies of water. Generally seeps are found on the edges of continental slopes where the earth's crust is bending and folding. Unlike hydrothermal vents cold seeps are not due to magma heating seawater and expelling it back out of the ground. Seeps form in places where a lot of plant and animal matter has settled to the bottom, become buried, and decayed. As that material breaks down it makes a lot of methane gas. Then as the ground bends it squeezes the gas, pushing it closer to the surface through the soft sediments on top. My apologies for being crass, but yes, the earth does fart.


A stream of bubbles escapes from the ground at a cold seep
Courtesy Deepwater Canyons 2013 - Pathways to the Abyss NOAA-OER/BOEM/USGS

The gas alone is not enough to establish an ecosystem; some organism needs to harvest the gaseous bounty to start a food chain. On land and in the surface waters, plants convert the sun's energy into chemical energy using CO2. At cold seeps bacteria and archaea convert the energy in the methane (CH4) coming from underground, and sulfate in seawater, to a type they can use. In a spectacular bit of symbiosis the archaea manipulate the methane and the bacteria manipulate the sulfate, then they use one another's products to complete their energy conversion. The exact nature of this back and forth isn't well understood, but scientists do know it produces hydrogen sulfide.

The hydrogen sulfide is then used by bacteria living inside animals to produce even more energy. These animals (some types of mussels, clams, and tube worms) have little to no digestive system. They get their energy straight from their symbiotic bacteria. At many cold seep sites large mats of bacteria and archaea are surrounded by these animals. Sometimes they even form a bulls-eye of different colors radiating out from the center.


Bacterial mats (white) and mussels (brown/orange) thriving at a cold seep
Courtesy NOAA Photo Library via Flickr

These large sedentary animals draw in small animals that take shelter in the jumbled chaos of their shells. Predators of those small organisms then come hunting. Many animals also feed directly on the bacterial mats, so there don't even have to be larger organisms around them. Entire ecosystems develop from the toots of the planet. Some of the animals that take advantage of cold seep environments are even ones that we eat, like sablefish and crabs. King crabs have even been observed feeding on bacterial mats, leaving, and coming back only after enough time has passed for the mats to regrow!

All of this biological activity helps contain methane (a potent heat trapping molecule) in the sea, keeping the temperature of the earth from rising even more. Also many seeps found in very deep water have low enough temperatures and high enough pressures for solid ice crystals to encase methane molecules. These "methane hydrates" also help keep carbon out of the atmosphere. You can see the biological and geological carbon traps interacting in this adorable video below.



Cold seeps are a good number of deep sea ecosystems, but there's more talk about, and even more to discover. Clearly the ocean bottom isn't quite so lifeless as we once believed. And probably it's even more full of life than we currently understand. Jurassic Park's Ian Malcom knew what he was talking about.

References:

Levin, Lisa, "Ecology of Cold Seep Sediments: Interactions of Fauna with Flow, Chemistry and Microbes", Oceanography and Marine Biology: An Annual Review, 2005, 43, 1-46, Taylor & Francis

Accessed via: http://levin.ucsd.edu/publications/Levin%20OMBAR%2005.pdf

Niemann et al., "Methane-Carbon Flow into the Benthic Food Web at Cold Seeps- A Case Study From the Costa Rica Subduction Zone", PLOS ONE, Oct. 2013, DOI: 10.1371/journal.pone.0074894

Accessed via: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0074894#pone.0074894-Niemann1

"Discovery of a New Chemosynthetic Community" NOAA Ocean Explorer

http://oceanexplorer.noaa.gov/explorations/13midatlantic/logs/may8/may8.html