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Unexpected silver lining seen in Earth’s bleached coral reefs

A close look into coral reefs along the Seychelles revealed quite a lot of nutritional value for fish even after suffering mass-bleaching events.

(CN) — A new study reveals bleached coral reefs can still provide local fish with key minerals, meaning millions of people in the tropics dependent on fishing will continue to enjoy nutrient-rich fish.

Of all the habitats and ecosystems beneath the ocean’s surface, few are as crucial as coral reefs. These underwater sanctuaries provide countless species of fish with food, protection from predators and even a place to rear their young, resulting in nearly a quarter of all ocean fish depending on coral reefs for their survival.

Humans also reap coral reef benefits. Some estimates say that nearly a half a billion people around the planet depend on coral reefs either for food or employment, not to mention the huge draw for local tourism industries.

But despite their clear importance to mankind and wildlife alike, many reefs have had a long and stressful past few decades. As ocean temperatures rise around the world due to climate change, the coral in the reefs can expel much of their algae and begin to die, resulting in the reefs losing much of their color and taking on a “bleached” appearance.

Experts and environmentalists have warned that bleached coral reefs could wreak havoc on local communities, but details on how the chemical makeup of the reefs change with bleaching had not been fully explored.

This changed when, in a study published Thursday in the journal One Earth, researchers revealed an exhaustive analysis on coral reefs to see how rising temperatures could change the nutritional composition of coral reefs and the fish that feed from them.

Their results, somewhat surprisingly, may give millions of people hope.

Data from Thursday’s study show that fish taken from small-scale fisheries in coral reefs are still full of vital micronutrients humans need to prevent malnourishment, even after those reefs experienced bleaching. In fact, researchers found that bleaching actually resulted in some minerals becoming more abundant, showing they may be more resilient to climate change than originally believed.

"Coral reef fish contain high levels of essential dietary nutrients such as iron and zinc, so contribute to healthy diets in places with high fish consumption,” said James Robinson, research fellow at Lancaster University who led the study. “We found that some micronutrient-rich reef species become more abundant after coral bleaching, enabling fisheries to supply nutritious food despite climate change impacts. Protecting catches from these local food systems should be a food security priority."

Experts made this startling discovery by looking at over two decades worth of data from the Seychelles, an area that lost nearly 90% of its coral after mass-bleaching events in the late 1990s. They found some of the reefs transformed after being bleached in ways that allowed new kinds of macroalgae, such as sargassum seaweed, to dominate the area.

Because fish are largely algal-feeding herbivores, experts suggest that chowing down on these new seaweeds resulted in fish from the coral fisheries with much higher amounts of key minerals like iron and zinc.

This news could come as a tremendous relief for people in tropical communities who heavily rely on these fish. Coastal people in tropical areas have historically higher rates of malnourishment and anemia, making these nutrient-heavy fish an invaluable resource for their communities.

Study co-author Christina Hicks says these results are extremely promising for people in tropical areas as the world continues to fight to effects of climate change, but that it will still be up to us to ensure that fisheries are sustainably and responsibly managed going forward to ensure these advantages are not wasted.

“Fish are now recognized as critical to alleviating malnutrition, particularly in the tropics where diets can lack up to 50% of the micronutrients needed for healthy growth,” Hicks said in a statement accompanying the study. “This work is promising because it suggests reef fisheries will continue to play a crucial role, even in the face of climate change, and highlights the vital importance of investing in sustainable fisheries management.”

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