Bleached coral reefs are still home to nutritious fish

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One of the most visible impacts of climate change is coral bleaching. As temperatures rise around the world, the water temperature also rises, causing stress and stress of colored coral expel their symbiotic algae partners. These events leave reefs without their primary source of food and susceptible to disease.

We have seen this happen several times in recent history. In 2020, the Great Barrier Reef off Queensland, Australia, experienced its third major bleaching event in just five years-and he could see another by the end of this month. In some cases, the bleaching is so intense that it leads to high mortality. The decline of reefs impacts the fish communities that live there, as well as the populations that depend on the reefs. for food or income.

In 1998, the African archipelago of Seychelles experienced a massive heat wave that caused almost all corals in the region to disappear. Researchers who have assessed the impacts of the disaster over the past 20 years have learned that about half of the reefs have recovered, while the other half have been replaced by algae. But more recently, an international team of scientists found that fish populations, even those swimming around the most damaged corals, were considerably healthier than expected, at least in terms of nutritional value for humans. They published their discoveries yesterday at A land.

[Related: Fish sounds tell us about underwater reefs—but we need better tech to really listen]

“The Seychelles is a great place to study how fish contributes to people’s health, because a lot of people eat fish,” says James Robinson, coral reef ecologist at Lancaster University in the UK and lead author of the article.

Robinson went out in search of fish with a handful of local fishermen and captured samples of 43 tropical reef species in reclaimed and algae infested areas. He and his fellow researchers then sent sections of the subjects’ frozen muscles to analyze things like the concentration of minerals and fatty acids.

“We first wanted to understand how nutritious reef fish are, so we took all of these values ​​and compared them to other meats like chicken, pork and beef,” says Robinson. “What we found is that reef fish are similar or more nutritious than these meats… it was super cool, finding out about the role reefs play in people’s health.”

Fish still thrive on Seychelles’ coral reefs, which is important to the humans living on the islands. Professor Nick Graham, Lancaster University

But they also discovered something strange: Besides being generally healthy, reedfish were more nutritious after blanching than before. After comparing the data, the study authors found an increase in fish biomass and a corresponding increase in nutrients in today’s fish compared to pre-1998 fish.

In addition, fish from reefs rich in algae had more iron and zinc than the same species at reclaiming coral sites. The significant change in the food web, evolving into nutrient-rich macroalgae, has “spread” up the food chain to anything that eats the algae, Robinson says.

“It sort of means that Seychelles’ reefs continue to provide food despite these really severe climate impacts,” Robinson said.

However, not all bleached reefs give in to productive algae—sometimes they are replaced by grassy turf algae, which has not yet been studied in this method. So there is always the possibility that other whitening events, like those of recent years, may not see the same nutritional silver lining. Yet this research underscores the importance of protecting coral reefs as part of the protection of the food system, even after climate impacts.

Currently, Seychelles is heavily dependent on imports, with about 90 percent of their total food coming from outside the country. Globally, climate change poses a growing threat to food systems, whether due to lower agricultural yields Where annoying impacts on fishing.

“We have to ask ourselves if we can manage coral reefs to protect this food supply and understand how bleaching will affect it at the same time,” Robinson said. “Most reefs are not managed for fishing, so there is a risk that if you fish too hard you lose that nutritional benefit. Hopefully this is another good reason to manage and protect reef fish. “

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