Conservation and Biodiversity

We’re hurting coral reefs, which means we can help recover them

Coral reefs provide homes to more than a quarter of marine life. Unfortunately, climate change warms and acidifies oceans, harming reefs and leaving many species without a home. But a study published last week in the journal Marine Biology reports that climate change is only part of the problem.

Warmer water temperatures can cause coral bleaching — the term for stressed coral that expel algae in their tissues — but these temperatures may not be the only cause: Fertilizers, topsoil and sewage may also threaten the health and long-term survival of coral reefs.

The authors of the study examined 30 years of data collected off the coast of the Florida Keys. They concluded increased nitrogen levels from land-based runoff as far north as Orlando also causes coral bleaching. These data were examined independent from increased water temperatures.

In other words, global coral bleaching is also a local problem, something that we may be able to manage right within our own cities and counties.

In a press release by Florida Atlantic University, Brian Lapointe, senior author of the study, points to solutions like improved sewage treatment, less fertilizer use and increased storm water storage as ways of softening our impact on coral reefs.

So, what’s actually happening here?

While coral may seem like a rock, it’s really an animal — and not just one animal. As the National Oceanic and Atmospheric Administration explains, hundreds to thousands of small animals called

polyps make up coral. To thrive, polyps benefit from algae called zooxanthellae that live within the polyps’ tissues.

These algae feed off the coral’s waste, producing sugars and other organic products, which the coral need to survive. The relationship is one of nature’s best examples of mutual symbiosis, where both organisms benefit from the other’s existence.

When corals are stressed — like by increased nitrogen levels — corals release these algae and turn transparent, revealing their white skeleton, which is why we call it bleaching. When corals are bleached, they are not dead, but they are more vulnerable. As more corals become bleached by environmental events like climate change and nutrient runoff, all their benefits, from the ecosystems they provide to the tourism they create, are also at risk.

But there’s hope

That local human activity is directly linked to coral bleaching should give us hope: If we simply change how we farm and fertilize, we can help recover many of these reefs.

“Citing climate change as the exclusive cause of coral reef demise worldwide misses the critical point that water quality plays a role, too,” said James W. Porter, co-author of the study, in the press release.

Climate change too often makes problems feel insurmountable, but as this study shows, we can curb many environmental problems in our own backyard. Start a conversation in your community, send letters your politicians and sign Earth Day Network’s pesticide pledge to stop using chemical pesticides and fertilizers. We can all chip in to protect coral reefs.

For more information, visit Earth Day Network’s coral reef page.

Featured image at top: Coral reefs provide homes to more than a quarter of marine life. Photo credit: Alexander Neufeld/Coral Restoration Foundation