Diving for Deep-Sea Coral Critters

Kara Capelli: You may be familiar with the shallow, colorful coral reefs found in tropical ecosystems. But did you know that similar organisms just as vibrant and diverse are also found hundreds of meters below the sea surface?

I'm here with Christina Kellogg, a research microbiologist with the USGS DISCOVRE program. Christina and other scientists get to travel hundreds of meters down into the ocean to study these organisms. Christina, how do these coral reefs differ from the reefs in tropical ecosystems?

Christina Kellogg: Well, the deep sea is a cold dark high pressure environment. The biggest difference between deep sea corals and shallow water corals is the lack of photosynthesis. Tropical coral reefs thrive because the corals have these photosynthetic algal symbionts, zooxanthellae that help feed them. But deep sea corals since they live in the dark don't have photosynthetic symbionts.

However, in the same way that all people have bacteria in their guts and on their skin without which they aren't healthy, all corals also have bacterial symbionts. And so one of my research questions is determining if the bacteria of deep sea corals play a big role in the coral's health and nutrition because there aren't these algal symbionts to help out.

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Christina Kellogg: A lot of the deep sea is sort of flat, featureless, soft- sediment bottom. And deep sea corals whether it's just a solitary one coral or a whole reef, provide complex three-dimensional structure and that serves as a habitat for all kinds of other organisms.

For example, these reefs provide habitat for juvenile fish of a bunch of commercially important species. And these reefs just become centers of biodiversity in the deep sea because the structure attracts and supports thousands of other species; fish, crabs, snails, worms, sponges, and not to name counting the microorganism that are associated with all that stuff.

Kara Capelli: Why is it important to understand how deep sea organisms interact?

Christina Kellogg: Well, it might sound cliche, but everything really is connected. If you're down there trying to just study one thing, inevitably it links to something else. I'm studying coral-associated bacteria because we don't understand how the coral interacts with its microbial symbionts. We're missing an important part of the corals total basic biology.

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And if we don't know how to handle the coral's biology, and if the keystone habitat forming species in this ecosystem, then at some point we really don't even understand the ecosystem. Another example are food webs. There's thousands of species found on deep reefs that are connected from the tiniest bacteria and up to the biggest fish by who's eating who and that controls the flow of energy and carbon within the whole ecosystem.

In many cases where these deep reefs seem to be is connected to surface levels of high productivity because certainly if there's high productivity at the surface eventually particles rain down and that provide food for the ecosystem from the bottom. So, there's definitely connections both from top to bottom and then in terms of say fish from bottom to top.

Kara Capelli: Besides being an important part of ocean ecosystems, what other value do these coral reefs have?

Christina Kellogg: I think we are still discovering the answers to that question. One example is that some of these deep sea corals can live hundreds to thousands of years and their skeleton preserve a record of past climate condition in ocean chemistry.

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Essentially there is an archive that lets us look into the past. Another example is that their sources of noble biodiversity. So, bacteria and vertebrates from extreme environments are often sources of unique natural compound that might be developed into pharmaceuticals or even enzymes or other biotechnical compound.

Kara Capelli: Christina, thank you so much for being here.

Christina Kellogg: Sure, you bet.

Kara Capelli: This podcast is a product of the US Geological Survey, Department of the Interior. Thanks for listening.