Reef Health and Butterflyfish: Picky Appetites Protect Fish From Corals Touched By Seaweed

Butterflyfishes are particularly picky about their food and shelter needs. While studying these tropical reef fish, researchers from the University of Delaware (UD) discovered they will avoid corals that have come in contact with seaweed, even when the seaweed is no longer present. This suggests the coral-seaweed interaction produces a chemical cue butterflyfishes know to steer clear of.

"Parents are always trying to find ways to add vegetables into their children's diet, by hiding extra carrots in tomato sauce, for example. But what if the child could smell the carrots even without seeing them?" Dixson said in the UD's release. "It's not about memory, there is something happening with the coral-seaweed interaction that makes the coral unattractive to butterflyfish."

Whether seaweed actually makes corals less nutritious for the fish or if the chemical defense corals use to fight off seaweed makes them taste bad remains unknown. Nonetheless, researchers note the negative coral-seaweed interaction could have a profound effect on other reef organisms.  

"Butterflyfish clearly have evolved the ability to detect changes or differences in coral reefs and are choosing habitat and food supplies based on these cues. If this pattern is present in other fish, it could have ramifications including putting undue pressure on healthy corals by overeating them while avoiding those they don't like" Dixson concluded. "We need to start understanding these interactive effects, especially the behavioral choices that could be exacerbating issues that we're not even thinking to give fish credit for."

Formerly healthy reefs teeming with marine life are quickly being converted into wastelands dominated by seaweeds. While micro-algae have a symbiotic relationship with coral, macro-algae, such as seaweed, competes with coral for space along a reef. Generally speaking, plant-eating fish keep seaweed growth in check. However, there seems to be fewer herbivores around to eat the seaweed, in part due to overfishing and reef degradation. In addition, agricultural runofffrom nitrogen-based fertilizer boosts seaweed overgrowth.

In the latest study, researchers videotaped and counted butterflyfish interactions with several reefs in Fiji. The test reefs had chemically active (Galaxaura filamentosa) and chemically inactive (Sargassum polycystum) seaweeds, while the control reefs did not have any seaweed at all. Since these marine reef fish are territorial, the experiment was conducted in multiple locations.

"Butterflyfish are kind of like the canary in the coal mine," Danielle Dixson, one of the study researchers and an assistant professor in the School of Marine Science and Policy at UD, explained in a news release. "When problems start to happen, they will be hit first because of their strong reliance on coral for food and shelter, so understanding their ecology is important before reefs become too degraded or just aren't there."

The study was recently published in the journal Scientific Reports. 

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