probiotics it has become a buzzword among nutritionists and wellness gurus. But did you know that coral reefs also benefit from probiotics?

These probiotics may not come in a brightly colored bottle with a selection of different flavors, but corals rely on a diverse supply of microorganisms just like the rest of us. Coral probiotics come in the form of fish poop, but not all fish poop is created equal when it comes to providing beneficial bacteria.

fish in coral reef
Fish feces can act as a “coral probiotic” on coral reefs.
Cartsen Grupstra

“coralivore [coral eating] fish are generally considered harmful because they bite into corals, sometimes damaging the coral in the process,” said Carsten Grupstra, a postdoctoral researcher at Boston University who studies the role of microbes in coral reef systems. news week. “But they have a bad reputation.”

In a study with researchers at Rice University in Texas, Grupstra and his team discovered that the feces of these fish actually contain a variety of different microorganisms with the potential to support coral health. Even more surprising, the feces of so-called herbivorous fish, which are thought to keep reefs healthy by removing algae and coral debris, contain a microbial suite that was harmful to corals.

“We were really surprised that herbivore/detritivore feces had such obvious negative effects on coral health, compared to corallivores feces,” Grupstra said.

For the study, the team placed fecal pellets from each fish on a coral fragment for up to 24 hours to monitor the effects. “When comparing the effects of fresh feces with sterilized feces controls [with no microbes]we were able to accurately test how microbial communities in fish feces, and not the physical properties of fecal pellets, affect coral health,” Grupstra said.

Corals are filter feeders, so they can absorb nutrients from fish feces, as well as beneficial microbes. However, reef fish are very plentiful and some defecate up to four times an hour, meaning corals can easily suffocate. Diseases can also be spread in feces.

Carsten Grupstra
Carsten Grupstra, a postdoctoral researcher at Boston University, collects fish.
Cartsen Grupstra

“Our motivation was to start to unravel the physical and microbial effects that fish feces can have on corals by using feces from two fish that we expected to have very different fecal microbial communities,” Grupstra said.

“Exactly how this feces may affect coral health—how often it serves as nutrition, suffocates coral polyps, and transfers microbiota—requires more research attention before we can make reliable claims about how fish feces generally affect the health of coral reefs. he said.

Although there are still many questions, there were clear differences between the different species of fish. Microbes in fresh faeces from herbivorous fish produced significantly more damage than faeces from coral-eating fish, compared to their respective controls. And the feces of coral-eating fish contained about twice as many beneficial bacteria and fewer disease-causing microbes than the feces of herbivores.

This complements the team’s previous research, which found that coral-eating bacteria also help with the dispersal of the photosynthetic algae that live within most coral structures and provide them with food.

“We found millions of living [algae] cells per milliliter of feces, suggesting that these fish may make these cells available for uptake by corals, similar to how pollinators disperse microbes among flowers and how herbivores disperse beneficial fungi among plants said Groupstra.

“The results of this [new] The study provides insight into how corals acquire beneficial microbes, and the findings can be used in the future to help coral reef conservation,” he said.

coral proiotics
The image shows microbial colonies grown from fish feces.
Cartsen Grupstra

Coral reefs are among the most biodiverse habitats on Earth. They provide a home for a quarter of all fish species on this planet and protect coastlines from storms and erosion. However, these important and delicate ecosystems are increasingly threatened.

“Coral reefs are threatened by climate change, pollution and overfishing,” Grupstra said. “Fish have important roles in coral reefs, but very little is known about how fish feces affect coral health.”

While this latest study may help inform future conservation projects, much remains to be done to understand how these results apply to the broader coral reef ecosystem.

“Laboratory conditions [used in this study] they are not representative of typical situations on the reef, and most of the feces may not harm the corals,” Grupstra said. “[In nature] feces can more frequently be broken up by waves or running water and/or fall off corals as soon as they land on them.”

coral reef with fish
Coral reef ecosystems are much more complex than a controlled laboratory environment, so it’s unclear how fish feces would affect corals in their natural environment.
Cartsen Grupstra

He continued: “Small crabs, shrimp, or brittle stars that live among the branches of corals may also manipulate or feed on fish feces, causing them to break off and avoid injury formation. More work is needed to prove how common it is for fish feces to cause injury versus how often corals benefit from the feces.”

Both Grupstra and her co-author, Adrienne Simoes Correa of ​​Rice University, said the results of this study may be surprising, but they don’t indicate that herbivorous fish are bad for coral reef ecosystems. Nor do they indicate that coral-eating fish are always beneficial.

“The impact of herbivorous/detritivorous and coral-eating fish can be beneficial in some ways and detrimental in others, depending on the species involved, their life stages/sizes, and other factors,” Correa said. news week.

“If we want to harness coral-fish interactions to increase reef resilience, we will need to carefully test and monitor the results of the actions we take,” he said.

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