If coral reefs go, so will much of marine biodiversity

Coral reefs are among the most biodiverse places on the planet. Regarded as the rainforests of the seas, reefs teem with a myriad of species that live symbiotically in relatively small areas. Reefs cover less than 1% of the ocean floor yet harbor a quarter of all known marine species.

“[T]he variety of species living on coral reefs is greater than almost anywhere else in the world,” the National Oceanic and Atmospheric Administration in the United States notes. “Scientists estimate that more than one million species of plants and animals are associated with coral reef ecosystems.”

Yet corals are fragile creatures and climate change-driven warming water temperatures across the tropics are wreaking havoc with reefs. Most of the planet’s reefs will be dead and gone by 2050 unless we can find ways to save them.

Efforts are underway to do so. Proposed solutions fall into two broad categories: 1) trying to keep stressed reefs cooler in their natural habitats through geoengineering, and 2) genetically engineering hardier corals that can withstand higher temperatures.

Keeping reefs cooler artificially could be done by, for instance, shooting tiny droplets of salt into clouds above them in order to increase the ability of the clouds to reflect sunlight back into space and so keep seawater cooler. Other experts foresee planting heat-resistant corals into reefs and growing hardier corals in labs in an effort to rejuvenate reefs.

Scientists are also working to unravel the biochemical mechanisms between corals and the species of algae that live on them symbiotically. By understanding the specific metabolic pathways, the experts hope to discover ways to merge corals with more heat-resistant species of algae with the aim of preventing large-scale bleaching on reefs.

Genetic engineering could be the only way we might be able to save dying reefs. Recently, a Brazilian researcher managed to enable corals to withstand the effects of oil spills by inoculating them with a cocktail of 10 hydrocarbon-eating bacteria. In yet another recent breakthrough researchers reproduced the complex life cycle of spawning corals in a London aquarium.

Time is pressing. Coral reefs are among the planet’s most biodiverse ecosystems with numerous species of marine plants and animals living symbiotically on them. Yet bleaching can easily upset the delicate balance of these finely tuned systems. Scientists working in the Seychelles have reported that repeated bleaching events have long-term effects on fish communities in the area.

A single bleaching episode in the Seychelles in 1998 caused fish species large and small, including snappers and damselfish, to decline in number to an alarming degree. They were replaced by species of seaweed-eating fish which took advantage of seaweed that started flourishing in place of the corals.

The scientists found that the reefs and their ecosystems were unable to recover for nearly two decades when another bleaching event occurred. In other words, coral bleaching affects fish species living at coral reefs and can trigger long-lasting consequences in local biodiversity.

“Although the 18-year period between [two] major mass bleaching events allowed corals to recover on some reefs, we found evidence that fish populations were not able to return to their pre-bleaching levels, and they were substantially altered on the reefs that become dominated by seaweeds,” explains James Robinson, a scientist at Lancaster University who was the lead author of a study published in the journal Global Change Biology.

The outcome of repeated bleaching episodes will be fewer species of fish with herbivores and invertebrate feeding fish dominating at dying reefs where until recently a far larger variety of species thrived. “This will alter the way coral reefs function, and the fishery opportunities for coastal communities adjacent to coral reefs,” said Prof. Nick Graham, of Lancaster University in a press release.