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Biologist Brad Seibel Discusses Chemosynthesis

Institute for Exploration / Ocean Exploration Trust

One of the features that has attracted the Corps of Exploration to Eratosthenes is the presence of fluid seeps and the chemosynthetic communities that develop around them.

Chemosynthesis is a process analogous to photosynthesis that certain bacteria use to produce carbohydrate energy. However, unlike photosynthesis, in the deep sea these bacteria have no access to sunlight, so they create this energy by harvesting chemicals which seep up through the Earth's crust. The organisms that use chemosynthesis are found around fluid vents mostly located on the sides of the seamount. As Eratosthenes is being “squeezed” in its resistance to subduction (see my earlier blog on the geology of Eratosthenes) these chemicals mix with and enrich the waters as they seep out.

Chemosynthetic bacteria provide the foundation for entire communities of organisms. Two organisms within these communities at Eratosthenes are the tubeworm and a clam that we have yet to describe. I sat down with biologist Brad Seibel to get a better understanding of chemosynthetic communities or organisms.

“So Brad, tell me about the about the tube worms that we sampled from the seamount.”

“Tube worms are entirely dependent on chemosynthesis. They lack a mouth, they do not have a gut, all of their energy comes from a symbiotic relationship with chemosynthesizing bacteria that they hold inside their bodies. The animal has a gill that they stick out of their tube, called a plume, that harvests both the chemical compounds from the water as well as the oxygen and transport them to the bacteria with produce sugars in the same way plants produce sugars from photosynthesis.”

“We've also sampled clams from areas that were so rich with chemical fluids that enormous communities of organisms live there. Do these clams live in the same way with chemosynthetic bacteria?”

“They are likely a bit different, as they are more likely using methane, but yes they live in a symbiotic relationship with the chemosynthesizing bacteria. Bivalves are filter feeders, so these clams are mostly likely harvesting some energy from the surrounding waters, but we're not sure to what extent. The clams are also likely using hydrogen sulfide.  Some bivalves are capable of using methane instead, but these are probably using sulfide.”

“And do the fish and clams that we've found near these fluid seeps most likely feed on these tube worms and clams or are they feeding on matter falling from the surface?”

“I think most of the animals that we've found around the vents are surviving on the tube worms and clams and any other symbiotic organisms. So the chemosynthetic bacteria are the basis of the food web, and everything else is living from the energy they produce. The reason I say that is that the biomass is so great here in comparison to other areas that we surveyed, it would seem that most of the energy is coming from the seeps.”