How Fish And Clean Water Can Protect Coral Reefs From Warming Oceans

Nice to see you: parrotfishes prey on seaweed, which consume seaweeds that can outcompete, smother or even poison corals. Corinne Fuchs, Author provided

Hurricanes and waterspouts. Bone-chilling rain and 100 degree Fahrenheit temperatures. Jellyfish and fire coral stings. Broken toes, shoulders, knees and fingers. Entanglements in fishing gear and stranded boats. Cockroaches, mosquitoes and sandflies. Hundreds of SCUBA dives and thousands of hours underwater. And to end it all, mountains of very different kinds of data to integrate.

These are just a few of the challenges we ran up against on our four-year endeavor to ask the the not-so-simple question: “How do three human factors – overfishing, pollution and climate change – intersect to cause the decline of coral reefs?”

By looking at the microbial communities that live on corals, our research uncovered a crucial role that fishes play in protecting coral reefs. We also discovered that these fishes together with clean water may be a vital buffer against the coral disease and decline caused by climate change-induced warming ocean waters.

Coral reef decline and human impacts

You may have seen that the plight of the world’s coral reefs, pinnacles of marine biodiversity, has been in the news a lot lately.

Currently, El Niño-driven increases in ocean temperatures are causing a third worldwide coral bleaching event. Australia’s Great Barrier Reef, one of most protected and largest coral reefs in the world, may lose a third of all its corals. Jarvis, a remote U.S.-protected island, is suffering an unimaginable 90 percent coral mortality.

While this recent bad news for reefs is eye-catching, coral reefs have been in trouble for a long time. Many reefs around the world have seen gradual declines in corals over the past two to three decades.

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The Conversation

Scientists sampled the microbial community, or microbiome, around coral reefs to gauge the global and local factors that affect reef health. Becky Vega Thurber, Author provided

The decline in corals has many culprits, but they can be classified as two major kinds, local and global stressors. Local stressors involve aspects of human activity that impact reefs on a small regional scale, while global stressors can impact reefs over the entire planet. Local stressors are things like overfishing, pollution and sedimentation from coastal development; they may kill corals all by themselves.

But these local factors never occur in a vacuum. It is likely these local human impacts combine with the ubiquitous ongoing global stressors such as warming oceans and ocean acidification that drive the huge bleaching events we are witnessing today. Yet although we know they occur simultaneously, scientists have rarely investigated the effects of these combined local and global stressors on coral reefs, outside of simplified and unrealistic lab-based experiments that are generally short in duration.

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