A new study by researchers at UGA and Florida International University has found that the elimination of large marine predators through overfishing and habitat alteration removes a vital source of nutrients for coastal ecosystems.
The study, currently in press in the journal Ecological Applications, shows that the influence of these large marine species goes far beyond their role as predators.
“The effects are not just top-down,” said study co-author Jacob Allgeier, a doctoral student in the UGA Odum School of Ecology who led the study with Craig Layman of FIU. “When you eliminate these large predators, you also eliminate a major source of nutrients for algae and plants in the food web, especially in tropical and sub-tropical coastal areas.”
Working at study sites on Andros Island in the Bahamas, the team, which included UGA associate professor of ecology Amy Rosemond, compared populations of gray snapper from areas that experience varying levels of human impact, specifically overfishing and habitat alteration.
Tropical and sub-tropical coastal waters are typically low in nutrients, according to Allgeier. That’s why the water is clear and why the fish are so important, he said. “They recycle the nutrients they take in from the food that they eat, making them available for lower-level organisms, like algae, that form the base of the food web.”
The researchers found significantly higher fish densities at the sites that experienced no human impacts, which led to much higher quantities of nutrients being recycled at these sites: 4.6 times more nitrogen and 5.4 times more phosphorus.
“We were surprised at the quantity of nutrients supplied by the fish,” said Allgeier.