Madagascar RAP: Corals + Climate Change

As part of a CI-organized Rapid Assessment Program (RAP) off the northeastern coast of Madagascar, an international team of marine scientists is spending three weeks exploring ecosystems, documenting species – and reporting back to us about what they’ve found. Read all of the team’s posts from the field here.

Where do the days go? Time crawls by with the routine and lack of personal space, yet suddenly we’re almost at the end of 19 days of work! Now we’ve set sail with the trade wind behind us, on our way back north to Ambodivahibe where I wrote from at the start of the trip.

So what have the corals been like? This is one of the most exposed and difficult-to-work coastlines I’ve ever experienced. The wind and waves roll in out of the southern Indian Ocean, pounding the narrow reefs along the coastline. Madagascar’s famous soils that color the rivers brown with silt are as active here as elsewhere on the island. As a result, we have been diving either in silty waters with only five meters of visibility (if we’re lucky), or on outer reefs pounded by waves, trying to squeak in a first dive before the wind picks up at 9 AM.

My first impression was that the hard coral diversity was lower than I had expected. But after three weeks of diving, the numbers have climbed past 270 species – approaching the highest that I’ve yet seen in East Africa, but not quite as high as those from Madagascar’s northwest coast. However, we have found three of the rarest corals endemic to the western Indian Ocean – Anomastrea irregularis, Horastrea indica and Gyrosmilia interrupta – present in greater abundance than I’ve ever seen.

As a coral scientist, there are two things I found most interesting about the area we surveyed. First was the way in which physical conditions shape coral reef development. The reefs are squeezed into narrow belts on the steep coastline, in murky bays and on open coasts battered by waves and wind. There are almost no lagoon and back reef areas that you find in many fringing and barrier reef systems. Also, because of the turbid waters, the maximum depth of coral growth is limited to about 20-25 meters. It’s no wonder the species count is a little low!

Second, our trip has coincided with an unusually warm summer season in this part of the Indian Ocean, caused by a moderate El Niño hanging over the Pacific. Corals turn white when stressed, called “bleaching,” especially in response to high temperatures. The previous RAPs had identified Ambodivahibe as being protected from high temperatures by its deep submarine canyon and strong onshore winds and currents, which cause upwelling of deep cold water. In 2006 the RAP team observed large corals that had survived the coral bleaching event of early 1998 which affected most of the region.

On this trip, we found bleaching all along our survey route, but it was not as intense as I had anticipated, affecting 30 percent of corals at the most. And the good news for the corals (though not for us, as the rough conditions made our work VERY difficult) was that the southeast monsoon winds started a month earlier than normal, putting an end to the high temperatures and releasing the corals from any further stress.

It looks like turbidity from the coastal rivers – traditionally thought to be bad for corals – shelters them from high light intensities, which act in synergy with high temperatures to cause bleaching. So along with the deep canyon at Ambodivahibe, the coastal rivers and bays further down the coast also shelter corals from high temperature stress and bleaching, giving them some protection from the effects of climate change.

So that’s that…now comes the harder job of working up the coral species identifications, struggling with some potentially new ones, and writing up the reports. But first, a massive dinner in Diego…and a SHOWER!!!!

David Obura is the chief scientist of the RAP and a coral expert. He is director of CORDIO East Africa based in Mombasa, Kenya.

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