According to new research, the feces of coral-eating fish may function as "probiotics" for reefs.

Originally, it was considered that corallivore (fish that consume coral, such as pufferfish, parrotfish, and butterfly fish) degraded marine surfaces. According to a study, they are part of a cycle that redistributes beneficial microorganisms that can help coral survive by consuming some sections of the coral and then pooing in various regions of the reef.

Dr. Carsten Grupstra, of Rice University, the lead author of the study explained that fish are often thought to be dangerous because they bite the corals. But it turns out that this isn't the complete picture.

Grupstra elaborated that "Corallivore feces contain many of the bacterial taxa that associate with healthy corals under normal conditions, potentially resulting in the natural dispersal of ‘coral probiotics’, analogous to fecal microbiota transplantation therapy in humans.”

This means that when some fish feces interact with coral colonies on the reef, the bacteria in the waste can be transported to a new coral colony and be advantageous to that new coral colony.

The study, which was published this week in the journal Frontiers in Marine Science, looked at the various effects of grazer fish, which devour algae and debris. It was previously considered that they contributed to reef health, but the study discovered that grazer feces, which contain disease pathogens, may leave dead areas on corals known as lesions.

The scientists studied the impact of corallivore and grazer fish feces and discovered that grazers caused lesions or death in all coral pieces, but corallivore feces generated fewer and smaller lesions and seldom caused death. Furthermore, the corallivore feces helped disseminate beneficial microorganisms, which kept the reefs healthy.

The study sought to ascertain which types of bacteria were contributing to the observed effects on the coral, if the excrement included particular coral illnesses, and whether the results of the feces addition experiment could be transferred to other fish that ate coral, algae, and detritus.

Guptra stated that additional study in more natural circumstances was required, where factors like waves and other species may influence the results.

 “I think [at the moment] there hasn’t been a lot of research into fish species and how they affect corals, but this might be really important in coral reef ecology. We’ve seen some other labs publishing stuff about microbes in fish feces, so I really hope more people look into this because it’s interesting and could provide a new angle.”

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