Corals Hide From Climate Change Under Mangroves

A great number of coral populations across the globe have been steadily declining due to the adverse effects of climate change. The NOAA even recently recognized 20 different types of coral as threatened species due to notable decline. However, some coral have found themselves an ally. Mangroves appear to be harboring a great number of coral species, protecting them from things like ocean acidification and elevated temperatures.

According to a study recently published in the journal Biogeosciences, more than 30 species of reef corals were discovered growing in Hurricane Hole, a large mangrove habitat within the Virgin Islands Coral Reef National Monument in St. John.

The study details how these corals are not only prevalent, but healthy, benefiting from the protection that red mangrove trees are providing the reef-building colonies of invertebrates.

So how does this work? Coral across the Earth are being threatened by high levels of solar radiation and elevated water surface temperatures, which causes stressing, making them frail and susceptible to disease. This is best seen in the historic bleaching events that are currently happening around the Hawaiian islands.

At Hurricane Hole, however, the canopies of the red mangroves are simply keeping the coral and immediate water shaded, protecting them from this harm.

"When examining corals for this study, researchers found evidence of some species thriving under the mangroves while bleaching in unshaded areas outside of the mangroves," the US Geological Survey (USGS) reports. "Boulder brain corals, for example, were found in abundance under the mangroves and were healthy, while many of those in unshaded areas a short distance away were bleaching."

Corals are also under fire from encroaching ocean acidification, where the ocean's acidity has seen a 26 percent increase over the past 250 years and is expected to increase to a new level again within the next century, according to a recent UN report. This acidity eats away at the coral's stiff exteriors, weakening colonies and causing the animals to literally dissolve.

According to the scientists with the USGS and Eckerd College who assessed Hurricane Hole, a combination of chemical, biological and physical conditions around the mangrove habitats helps protect the corals by keeping acidity in the water below harmful levels.

The researchers say this is an unexpected adaptation that is certainly encouraging in the wake of massive coral decline.

Still, it is not known how many other mangrove areas in the world harbor such a high diversity of corals, as most people do not look for corals growing in these areas. This could be nothing more than a miraculous fluke, but even so, it is an oasis for coral in a drying world.