Coral bleaching may not end reef fisheries. But that’s the only good news

Coral reefs are among the most diverse marine ecosystems on the planet. Yet because climate change has been wreaking havoc with corals, the coastal communities in tropical regions that depend on these reefs for their livelihood are bound to lose out on much of their catch. Food security for millions of people are set to become severely undermined.

Or so it is commonly believed.

Yet according to a new study, published in the journal Nature Ecology and Evolution, even in the face of extreme coral bleaching local fisheries, at least in the Seychelles where the study was conducted, have remained stable.

A team of researchers, led by Lancaster University in the United Kingdom, analyzed data on fish abundance and local catches over a 20-year period to assess the long-term impacts of climate change-driven mass mortality in corals on nearshore artisanal coral reef fisheries in the Seychelles, an archipelago in the Indian Ocean. As part of their study, the researchers looked at more than 45,000 daily fishery landing records from 41 different sites and also conducted 960 underwater surveys at 12 locations.

“Contrary to expectations,” the researchers write, “total catch and mean catch rates were maintained or increased after coral bleaching, consistent with increasing abundance of herbivorous target species in underwater surveys, particularly on macroalgal-dominated reefs… [O]ur results show that climate-impacted reefs can still provide livelihoods and fish protein for coastal communities.”

However, the number of available species in areas with mass coral bleaching was found to have declined, limiting catches to fewer, largely herbivorous species. After a mass coral bleaching event in 1998, for instance, large swathes of coral habitat were across the Seychelles. Yet “reef fish catches have either remained the same and even increased,” the scientists note.

“Although many reefs became overgrown with seaweeds, increases in algal-feeding fish communities such as rabbitfish are enabling local fishers to continue harvesting food,” they add. In other words, the loss of corals facilitated the spread of seaweed, which drew fish that feed on them to the area in larger numbers.

“Bleaching in 1998 caused mass coral mortality, habitat collapse, and shifts to seaweed dominance on some reefs, and so we expected the fishery to be in decline,” James Robinson of Lancaster University’s Environment Centre explains. “But we overlooked the potential for algal-feeding fish to benefit from higher algal productivity. With coral bleaching events becoming more frequent and more intense as the climate warms, the unexpected news was that these fisheries continued to provide benefits for people.”

At the moment some 6 million people depend on fish at coral reefs in the tropics for their sustenance and livelihood. Fishermen land between 1.4 and 4.2 million tons in catches each year, based on estimates.

However, the findings of the study do not mean that all will well with tropical fisheries in coming years and decades. The longer-term effects of climate change, the scientists point out, may play out in unpredictable ways, leading to patchy catches in certain areas.

“These data from the Seychelles forewarn of changes likely for coral reef fisheries in other countries,” Prof. Nicholas Graham of Lancaster University, was a co-author of the study, cautions. “While the news for fishers is better than we might expect, the algal-covered reefs are in marked contrast to the complex coral habitats which once hosted myriad and diverse coral reef fishes.”