Coral reefs depend on waste products from larger fish such as barracudas, grouper and others, for nitrogen and phosphorous.

Coral reefs like this one depend on nitrogen and phosphorous found in fish waste. Photo: Shutterstock

Coral reefs are very delicate ecosystems, and we’ve known for some time that those with fewer large fish tend to grow much slower. This is because nutrients in reefs are sparse; they have what ecologists call tight nutrient cycles.

Nitrogen and phosphorus, essential nutrients that coral need in order to grow, come from their fish neighbors through their waste products.

The nutrients are introduced into water through fish gills and their urine, respectively. Large predatory fish, like barracudas, groupers, or jacks produce more of both, and in coral reefs where those fish are caught in higher numbers, the reefs suffer.

These larger fish provide far more nutrients than smaller fish do, and tend to spend their days nestled within the reefs, then go out at night to hunt. But when they are overfished, the reefs grow a lot slower. The biomass of fish living among a reef is essential to keeping that reef going which, of course, the fish need in order to survive as well.

Coral reefs face a lot of threats, especially from climate change, so finding ways to help preserve these delicate ecosystems is quite important. Further research, on reefs outside of the Caribbean, will help to understand reefs in other parts of the world.

It stands to reason that this kind of nutrient cycle or something very similar to it will be the standard elsewhere, so we need to find ways to preserve these delicate ecosystems. Finding ways to cut fishing in reefs to a sustainable level, coupled with ways to reintroduce certain species of fish to reefs where they have been severely reduced or even wiped out, is the obvious place to start.

With more research, hopefully scientists will be able to convince governments that these are worthwhile endeavors and find the funding needed to improve coral reef health across the world.