Coral reefs provide many species of fish shelter and protection. In return, fishes give back to the ecosystem by offering their urine.

A new research, which was published in the journal Nature Communications, revealed that the lack of fish urine is behind the lack of nutrients surrounding corals in waters where commercial fishing commonly occurs.

Fishes typically take shelter in and around corals during the day and pee out important nutrients. By night, they find food in and around the reef.

The setup offers mutual benefit for both fish and corals. When fish pee, they release phosphorus and nitrogen in the form of ammonium through their gills, which serve as important nutrients for coral reefs to grow.

The level of nutrients affects the health and growth of the coral reefs. Earlier research has shown that coral reefs with healthy fish populations tend to grow faster compared with those having smaller fish population.

Study researcher Jacob Allgeier, from the University of Washington's School of Aquatic and Fishery Sciences, noted the importance of animals in coral reefs, as they help move the nutrients around.

Fishes have a large proportion of the nutrients in a coral reef in their tissues, so they also play a role in recycling them. This means that if you remove fishes out, it would also mean removing nutrients from the ecosystem.

"Simply stated, fish biomass in coral reefs is being reduced by fishing pressure," Allgeier said. "If biomass is shrinking, there are fewer fish to pee."

For the new research, Allgeier and colleagues measured the nutrient levels at various corals reefs and found that the level of vital nutrients is higher in reefs with greater population of predatory fish, while the reefs with few big fishes have poor nutrient levels.

The researchers likewise found that the nitrogen output varies with body size among fishes and that carnivorous fishes tend to pee more phosphorus compared with the smaller herbivores.

The researchers said that they hope their research could help in the fight to protect coral reef ecosystems. Rebuilding communities of coral reef fish is very important in ensuring food security and livelihood of billions of people.

"We suggest that in addition to well-acknowledged conservation targets such as biodiversity protection, a broader perspective that incorporates predictable impacts of fishing pressure on nutrient dynamics is imperative for effective coral reef conservation and management," the researchers wrote in their study, which was published on Aug. 16.

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