By Kimberley Collins 18/08/2016

Scientists have known for decades that fish urine is important for coral reefs. Now, a new study has found urine excreted by large fish is critical to the survival and growth of these fragile ecosystems. 

Like most living things, coral reefs need nutrients to grow.

In coral reefs, fish provide these, holding the nutrients in their tissue and excreting them through their urine and gills.

Phosphorous is released into the water through their urine, while ammonium is excreted through their gills.

Coral Reef
Over 4,000 species of fish inhabit coral reefs (Photo by Wikimedia Commons)

Scientists have long known that both these nutrients are critical to coral reef growth. One study in the 1980s showed reefs with fish grew twice as fast as those without fish.

Now, a new study has shown the importance of large fish to coral reefs and looked at the impact removing them has on the entire ecosystem.

It’s widely known that fishing can have negative impacts on fish populations. But what happens to the ecosystem when they are removed is less explored.

The paper’s co-authors Jacob Algier, Abel Valdivia and Courtney Cox, surveyed 143 fish species at 110 sites across 43 Caribbean coral reefs.They looked at areas with a range of fishing pressures – from marine reserves to heavily fished reefs where few large fish remain.

They found that fishing didn’t reduce the number of fish species present, rather the number of large fish.

In sites where large fish were missing, nearly half the key nutrients were missing from the ecosystem.

This is an important step towards identifying how fishing effects nutrient capacity in coral reefs. It will be critical for informing future fisheries management to maintain health coral reefs.