Seaweed May Be Keeping Brazilian Ecosystem Afloat

A diver swims over a buraca covered with seaweed on Brazil's Abrolhos Bank.

A diver swims over a buraca covered with seaweed on Brazil's Abrolhos Bank. (© Enrico Marone/CI-Brazil)

Together with scientists from CI-Brazil, local universities, the New England Aquarium and Boston University, CI’s Les Kaufman is exploring Brazil’s Abrolhos Bank to learn more about its marine life and connection to local communities, the impact of climate change and how people can better protect the region. Read previous blogs from the trip.

We did it — we’ve succeeded in dodging the weather to complete the last three legs of our Abrolhos expedition. Four days of remotely operated vehicle (ROV) and drop camera exploration of the Abrolhos Bank, three days remote and scuba research on buracas on the eastern shelf, and several more days of sharing our discoveries with the press.

Matheus Freitas pilots the ROV over rhodolith beds covered by seaweed on Brazil's Abrolhos Bank.

Doctoral student Matheus Freitas expertly pilots the ROV over rhodolith beds covered by seaweed on Brazil's Abrolhos Bank. (© Enrico Marone/CI-Brazil)

As always, the sea has not failed to surprise, confuse, illuminate and reorient us. Moreover, it’s armed us to move ahead with better measures to conserve and benefit from all these new discoveries — realizing that Brazilians have been dependent upon these marine ecosystems all along, even if only a handful of people knew it.

On previous expeditions, side-scan sonar revealed that the area of hard seafloor on the Abrolhos Bank was 20 times larger than we’d once thought. The question is: What actually lives on this hard bottom? Is it all deep coral reef? Deep reefs with very high live coral coverage have been discovered elsewhere. We’d hoped it might be coral, as we are worried about the future of one brain coral in particular: Mussismilia brasiliensis, the major reef builder on the Abrolhos Bank which is found nowhere else in the ocean.

Journalist Herton Escobar photographs the reef at a depth of 32 meters (105 feet). © Enrico Marone/CI-Brazil

What we found in these newly explored areas appears to be mostly ancient reef framework, which is overgrown by diverse living organisms and — like other reefs — densely inhabited by fish. These outer shelf mesophotic reefs are interesting, vibrant and important to many things people care about — but the corals there are few and far between. That means that the Mussismilia reefs near shore are really important. These corals are located in the reefs most vulnerable to overfishing, deforestation, coastal pollution and overdevelopment; every effort must be made to nurture and protect them.

Some of the biggest surprises on the expedition were all about algae. We anticipated the rhodoliths; what we were unprepared for was the untold amount of seaweed. Brown, green and red fleshy algae carpeted rhodolith beds as far as the eye could see — and as near as we could tell, accounted for thousands of square miles of shelf habitat.

Tomtate school over the mouth of a big buraca, which is cloaked by a layer of floating seaweed atop meters of fermenting algae underneath.

Tomtate school over the mouth of a big buraca, which is cloaked by a layer of floating seaweed atop meters of fermenting algae underneath. (© Enrico Marone/CI-Brazil)

As for the buracas — large shafts in the seafloor — some of them become filled up with algal fronds, especially in summer. It takes a lot of seaweed to fill up an entire buraca. The seaweed ferments, releasing precious nutrients and generating a build-up of gas. While we were positioned over one particular buraca, a large amount of material was jettisoned, and made its way all the way to the surface beside the boat, releasing an overwhelming stench.

Although algae growth may not seem to be the most exciting of discoveries, the implication of this is profound. Buracas could play an important role in nutrient cycling on the outer shelf. Hovering over many buracas are enormous shoals of fish — mostly members of the grunt family. Most of these fish belong to one of two species: tomtate (Haemulon aurolineatum) and a form of white grunt (Haemulon plumieri) that is actually yellow. Though similar to other species, this fish may be a species unique to Brazil that has never been described by scientists. It would not be the first.

The Abrolhos expedition team.

The Abrolhos expedition team. (© Luis Carlos Júnior/CI-Brazil)

The field portion of our expedition has concluded. It was an amazing journey of discovery, with kudos to Rodrigo Moura and Guilherme Dutra for pulling off a monumental effort that involved at least three vessels, more than 60 scientists and stretched over two months offshore, with many complications, technical challenges and crew change-outs.

We have made some fantastic finds. Our conceptions of the great ecological machine that is Abrolhos — of what it is made of and how it works — has been expanded and transformed from the fuzzy early notions we carried with us out to sea, to a picture, now sharp and startling but still rife with mystery, of a huge new world.

Les Kaufman is a senior marine scientist for CI’s Marine Science program. His blogs are cross-posted on the New England Aquarium’s Global Explorers blog.

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