Studying Corals

Deep water corals, just like their relatives on the reefs, are an indication of a healthy ecosystem - but they also act as a coral climate calender,...
31 August 2008

Interview with 

Murray Roberts, Scottish Association for Marine Science, & Brendan Roark, Texas A&M University


Murray - These are so-called cold water corals or deep sea corals.  So these are a different animal to those you would find in tropical shallow water areas.  They're not reliant on sunlight, not directly anyway.  They're found in deep, cold, dark waters.  There are huge developments of these coral reefs off Norway, Scandinavia and their distribution extends down off Britain and Ireland, right across the Atlantic with patches on the Mid-Atlantic Ridge to the American side of the Atlantic off Florida, the Carolinas and round into the Gulf of Mexico.Coral Garden

Chris - If they live down there they're not photosynthetic.  How do they survive?

Murray - They're surviving on the food that's produced at the surface layers of the ocean, plant plankton.  That plant plankton captures energy from the sunlight just as plants do anywhere.  Animal plankton will consume that.  Some of the corals seem well-adapted to take that animal plankton and eat it - they're predatory.  Others seem quite well-adapted to taking remains of the plants that are brought down from the surface.  There has to be a critical link between a productive layer in the ocean and a physical mechanism in the sea that gets that and transports it down with fast water currents to the sea bed where the corals live.

Chris - So they're doing a pretty important job of actually translating material which is up at the top of the ocean into biomass, material which is fixed at the bottom of the ocean.

Murray - Yeah they are.  What they do in that process is lay down a skeleton.  The coral forms a skeleton and that makes a reef, a framework.  That forms a reef and that's effectively an underwater city, if you like with high-rise developments where many other species can find a niche.  They can find a place to live.  When we look at the numbers of species that live in these areas they're amazingly high.  Even in areas of the Atlantic that we've studied for the last 150 years we go out to sample these areas and find many species that have never been described before.

Chris - How deep are they down there?

Murray - It depends where you are.  They're distribution tracks certain types of seawater, certain characteristics of the sea water.  They can be anything from 200m down to 1000m typically.

Chris - How big are the individual coral structures?

Murray - The structures they form can grow very large.  Off Scandinavia they may grow to extend up to 13km in length.  They grow off the sea floor several metres in height.  In other places, in deeper waters we have evidence that coral structures have grown right back through time.  They'll grow, form a reef structure that traps sands and muds.  In glacial times the corals will die back and other kinds of sediments come in.  Then corals start growing again and this process repeats and repeats and repeats all the way back over 1.5-2 million years.  Those structures can be hundreds of metres in height.

Chris - Brendan Roark, you've been working on these corals.  How far back in time do they go if we've got it right?

Brendan - The carbonate structures that Murray was talking about can go back 2 million years.  Individual species or individual specimens we've shown with some of the proteinacious corals from the Pacific have life spans upwards of 2000-4000 years. Chris - Given it's that long-lived, what else can it tell us about the environment it's growing in?

Brendan - As Murray was talking about, the linkages from the surface ocean to the deep ocean are recorded in some of the different types of skeletons on the deep sea floors.  You have two different kinds of skeletons made by deep sea corals.  One is a proteinacious horn-like material and those are the long-lived organisms typically.  That skeleton can record what's going on in the surface ocean.  In other words it's deriving all of its carbon from particular matter from the surface ocean.  You contrast that with typical carbonate skeleton that corals deposit: those are recording the ambient conditions of where the coral is living.

Chris - It's a bit like tree rings then, isn't it?

Brendan - It's exactly like tree rings.  Most of the corals have growth rings.

Chris - So you've got this really powerful, high resolution coral clock which is tracking back what's going on chemically in the ocean for 1000s of years.  How far could you take that back, though?  A big problem with climate change and ocean temperature models is that we're stuck in the near-term since we've been recording things, aren't we?

Brendan - By collecting dead specimens as well, we have with the gold corals continuous records overlapping the same way you would with tree rings going back 5000 years.  We have a few specimens that are as old as ten thousand years.

Chris - What about on the longer time scale though?  You said these corals live thousands of years and they may even be millions of years in terms of the time they've been growing where they are.  Can you go back literally millions of years?

Brendan - Yes, you can go back millions of years with the drilling in the carbonate mounds.

Chris - Murray, how are you setting about to try and study and improve our understanding of these corals?

Murray - What we're trying to do is set up a transatlantic coral ecosystem study.  The idea here is to firstly unify the research right across the Atlantic so that we take advantage of the very exciting place we are right now after ten or fifteen years of work: understanding where the habitats are and mapping them.  We're able to go to places within the Atlantic ocean and find carbonate mounds, cold water coral reefs, the kinds of species that Brendan has been talking about, and sample them and bring them into a large study to look at that climate history right across the Atlantic.  Also we want to tackle other questions as well.  We know they're diverse ecosystems.  A thousand species just in the North Atlantic.  A number that keeps going up with more and more studies.  We've not yet tried to compare that diversity across the Atlantic to understand where these species are found.  We haven't tried to compare right across the Atlantic how they're connected genetically.  Do we have one area that is the source of the larvae that then disperse across the Atlantic or are they growing in certain areas in isolation from one-another?  These are the kinds of questions you can only approach on a big scale.  Also to take the most advantage of the expensive resources that are needed for this work we want to share that internationally.  If, for the sake of argument, a German ship goes to sea then we're able to take American and Canadian scientists along so they can get the samples that they need.  Equally when an American ship goes to sea we want to see European scientists working alongside so we get the most benefit from the investment that we're making here.

Chris - When do you think we're going to see a return on the investment?

Murray - The project starts now.  We have our first sea-going planned in October.  We want to keep this going for four to five years.  We think that within about three-to-four years we'll have our initial results.  Of course, as with any project like this the writing period and the analysis period will begin.  We'll see the big results coming out in about five years from now we hope.


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