1998 was a terrible year for coral reefs. Abnormally high sea-surface temperatures led to large-scale bleaching of corals around the world. The oceans lost over 15% of its coral cover and some countries —Maldives for example—as high as 90%. Indian waters, too, were affected: around the Lakshadweep islands, coral cover was reduced to 5-10%.

But this extreme weather event also had a silver lining: it provided scientists with a rare opportunity to answer to an important question—how is a biological community assembled from scratch? Most of the time, the answer involves much guesswork and uncertainty because it is based on reconstruction of past events that scientists weren’t direct witness to. In this case, however, they could document the process of community assembly as it unfolded. This is exactly what Arthur and his colleagues from India and Spain did, in the bleached reefs around the Lakshadweep islands. Through careful and regular monitoring spanning 15 years following the 1998 event, the team painted a detailed picture of the recovery of Lakshadweep’s coral reef fish. A picture that is, unfortunately, not pretty.

Arthur and his team classified fish species into feeding types—starting with algal feeders and working their way up the trophic levels to top predators that feed on other fish—and examined how each type fared in the recovery process. They found a clear and striking pattern of trophic downgrading: fish of higher trophic levels were much more likely to go extinct than those of lower trophic levels. We knew, earlier, that human activities in the oceans, such as targeted fisheries, can cause downgrading. Now, through the work of Arthur and his team, we know that natural disturbances can also result in similar downgrading. These results are especially significant and worrying given that most of the world’s coral reefs are subject to both human and natural disturbances—a double whammy for coral reef top predators.

Further reading:

Alonso D, A PinyolGallem, T Alcoverro and R Arthur. 2015. Fish community reassembly after a coral mass mortality: higher trophic groups are subject to increased rates of extinction, Ecology Letters, 18: 451–461 DOI: 10.1111/ ele.12426.