Ohio State University biologists have discovered that fatter coral survive better over the long-term than their skinny counterparts. We're not talking about size, here, but actual fat deposits. Much like a human body survives on fat resources when on a diet, coral feed off their fat stores when deprived of the food they need to survive, especially during climate-related "bleaching" events.

As climate change causes rising ocean temperatures, stressed coral are unable to produce the salts and carbon dioxide that feed the algae that live inside the reefs. This disrupts the symbiotic "you scratch my back, I scratch yours" relationship between coral and algae, as the algae is expelled from its home due to lack of food.

Algae give coral its energy and its color (naturally, it is white), so their absence causes a "bleaching" effect. During this process, the coral, which are actually classified as marine animals, are essentially starved of their most precious food source—the sugar algae creates and shares with them. And like a human on a sudden diet, their bodies turn to their stores of excess weight to continue metabolic processes. The fat content improves the coral's chance of surviving during this fasting period, and recuperating faster than its leaner friends.

This research builds on previous work showing that fatter corals survived better in the short term. Now that these biologists have had longer to investigate the phenomenon, they have determined that these coral also do better in the long run, even a year after a bleaching event.

"Three global bleaching events have already occurred since the 1980s, and will likely occur annually starting later this century," said the study's lead author Verena Schoepf, in a press release. "Therefore, it has become more urgent than ever to know how coral can survive annual bleaching—one of the major threats to coral reefs today."

Ironically, the delicately named "finger coral" stores the most fat, and so is the most resilient to bleaching, while "boulder coral," which you would think would be pretty rotund, stores less fat and thus is less able to recover from a bleaching event. The new research showed that the least resilient coral was "mustard hill coral," which after an entire year since the bleaching, still hasn't recovered. Mustard hill coral stores the least fat of the bunch.

Interestingly, all three coral samples look healthy on a cursory glance—algae has returned and brightened the colors of all three samples. But just like the cheerleaders I knew in high school, their inner lives are a completely different story.

"They all look healthy on the outside, but they're not all healthy on the inside," said Andréa Grottoli, a principal investigator of the study. 

The research will help future investigators predict which coral will be hit the hardest by warming waters and other bleaching factors, including the alleged effects of sunscreen on reefs.

The research was published this week in the Proceedings of the Royal Society B: Biological Sciences.

Photo: James St. John | Flickr

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