Friday, April 6, 2012

Brazil: Rhodoliths and inverted reefs

Les Kaufman, New England Aquarium research scholar, is in northern Brazil to study the unique marine habitats of the Abrolhos Shelf with scientists from Conservation International and local universities. He and fellow researchers intend to learn more about the marine life of Abrolhos, its links with terrestrial communities, how both are likely to be affected by global climate change and what people can do to protect this special place and oceans worldwide.

We have just returned to Conservation International's office in Bahia from three days at sea where our team explored the deep, central shelf using technical diving and a remote operated vehicle (ROV).

This region is a vast carpet of rhodoliths: roughly spherical objects constructed by many layers of hard red algae. Rhodolith fields like this one represent a reservoir of carbon that could play a significant role in regulating global climate - but to know just what that role might be, and how significant a role, we must learn more about them.

Diver over rhodolith field, one dive's booty of deep rhodoliths. Photo credit: Dr. Rodrigo Moura

Rhodoliths were brought to the surface from depths of 70 to 80 meters (230 to 262 feet) by divers using a special gas mix that reduces the chances of decompression sickness, also known as the bends. When we opened the rhodoliths, we saw that boring by excavating sponges, clams and other organisms is minimal — a sign that the carbon may be stable and not quickly reentering the ocean, and then the atmosphere.

One scientist on our expedition is studying the creatures that live in and on the rhodoliths, many of which appear to also be species that also live on coral reefs. Other scientists are using the rhodoliths to study changes in ocean and coastal conditions over time.

The other big item bagged in the last few days is a collection of specimens from buracas — deep holes in the outer Abrolhos Bank. Buracas are often full of fish, and so we want to get a better look at their function as "inverted coral reefs" and learn how they are formed.

Divers breathing tri-mix (oxygen, helium, nitrogen) inside a buraca, depth at the lip of the buraca about 70 meters (approximately 230 feet). Photo: Dr. Rodrigo Moura

Today, we head out for another four days of reconnaissance using the ROV — exploring places we still know little about, some of which are in areas where greater protection has been proposed. 

Echogram of a buraca, or deep hole in the continental shelf. Such holes are sometimes filled with rhodoliths, while the walls are ancient coral reef framework, about 30,000 years old.

The weather is promising and our new course is plotted, so out we go for the next Brazilian adventure at sea.


Les is also working with Conservation International during this expedition. His entries are cross posted on their blog.

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