Scientists discovered the essential role of fish pee for the coral reef. The reason is that the liquid contains phosphorus, which combined with nitrogen is crucial to the growth of corals.
The researchers began with studying the zones where the fishes were scarce because of heavy fishing. The waters lacked half of the nutrients needed to maintain the health of the coral ecosystems.
“Fish hold a large proportion, if not most, of the nutrients in a coral reef in their tissue, and they’re also in charge of recycling them. If you take the big fish out, you’re removing all of those nutrients from the ecosystem,” said Jacob Allgeier, a postdoctoral researcher at the University of Washington’s School of Aquatic and Fishery Sciences.
The authors of the study monitored 110 sites from the Caribbean coral reefs, focusing on 143 fish species. Some sites had been declared marine preserves, and they had an intact population of fish. However, others have been heavily impacted by fishing.
The results showed that the sites with large marine predators had healthy levels of nutrients. The absence of large fish reduced the nutritive quality of the water almost to half. The most important substances were phosphorus or nitrogen.
The species of fish that are most important to the coral ecosystem are the grouper, the barracuda, and the snapper.
During the day, the large fish hide in the coral reef, and during the night they look for food in the reef communities.
A study for 1983 previously showed that the schools of fish that peed on the corals during the day were increasing the growth rate of the corals up to twice when compared to the reefs without schools of fish.
The new study focused on the quantity of nutrients released by the fish. The researcher built a giant data base with the size of the fish and the nutrient output. The measurements were made by catching the fish and keeping it in a plastic bag for 30 minutes, then measuring the nutrient quantity.
At the end of the monitoring, the researchers concluded that the amount of the nutrients depended on the size of the fish. Another conclusion was that carnivorous fish pee had more phosphorus than the smaller herbivorous creatures.
The models created by the researchers will be used by other scientists to estimate the quantity of nutrients available in different coral reefs, which will make them better assess the impact of fishing and the need to colonize sites with a specific fish species.
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