Coral reefs must strike a delicate balance in order to function

Coral reefs are often described by scientists as the rainforests of the ocean, since they host a high diversity of species and play a fundamental role in the proper functioning of marine ecosystems. Recently, climate change and local threats such as overfishing have caused a marked global decline in corals, making researchers ponder whether our planet will still have healthy, functional reefs in the near future. However, it is not yet clear what makes a coral reef functional.

By analyzing more than 500 coral reefs worldwide, a new study led by the University of Hawai’I at Mānoa has argued that five key functions performed by fish communities residing in coral reefs – the removal of algae, predation, biomass production, and the cycling of phosphorous and nitrogen – are inherently interconnected and need to remain in a delicate balance in order for the reefs to function properly. According to the scientists, while the performance of these processes is influenced by the community structure of fishes in any given reef, no reef can maximize all of the processes simultaneously.

“Imagine a coral reef fish community swirling with small fishes that feed on algae,” said study lead author Nina Schiettekatte, a postdoctoral fellow at UH Mānoa. “This community will be characterized by high algal consumption and high biomass production, but it will have low phosphorus cycling because these species excrete very little phosphorus.”

The discovery that no coral reef can excel in all functions led researchers to wonder whether there is a certain set of species that is more important than others in maintaining reef stability and health. Surprisingly, they found that no single species was consistently important in all locations where it was found, but half of all species played a crucial role in at least one location.

“This means that there are no global super-hero fish species for ecosystem functioning,” said study co-author Sébastien Villéger, a researcher at the National Center of Scientific Research (CNRS) in Montpellier, France. “But there are many local super heroes.”

“This work really changes the way we need to think about coral reef conservation,” added study co-author Simon Brandl, an assistant professor of Marine Ecology at the University of Texas at Austin. “Since we cannot maximize all aspects of functioning, we clearly need to develop a more nuanced approach to conserving coral reefs that considers local species, ecosystem dynamics, and stakeholder needs.”

The study is published in the journal Nature Ecology & Evolution.

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By Andrei Ionescu, Earth.com Staff Writer