Fish play a far more important role as contributors of nutrients to marine ecosystems than previously thought, according to researchers at UGA and Florida International University.
In a pair of papers in the journal Ecology, they show that fish contribute more nutrients to their local ecosystems than any other source-enough to cause changes in the growth rates of the organisms at the base of the food web.
Jacob Allgeier, a doctoral student in the Odum School of Ecology, and Craig Layman, associate professor at Florida International University, led the study, which took place in a large bay on Abaco Island, Bahamas.
To determine the impact of nutrients from fish, the team needed to compare sites with fish populations of different sizes. Knowing that fish tend to congregate around reefs-the larger the reef, the more fish it attracts-they built a series of artificial reefs of two sizes, large and small, and selected a number of control sites with no reefs at all.
Over the course of two years, they surveyed each site periodically to record the number, size and species of fish present. Allgeier created models to estimate the supply of nutrients from all species of fish at the various sites.
The researchers also measured the nutrient content and growth rate of seagrass. They weren’t surprised that seagrass at the large reefs grew faster and contained more nutrients than seagrass at the small reefs and control sites-but they were surprised at the magnitude of the difference and the extent to which it occurred.
The effect extended for roughly 3 meters around each large reef. The fish were contributing more nutrients than the seagrass could take in, allowing the excess nutrients to drift farther away from their source, fertilizing seagrass and algae in ever-widening areas.
The researchers anticipate this effect to extend farther with increased time.
Allgeier said the team’s findings further point to the importance of maintaining a healthy fish community, explaining that different types of fish contribute different amounts of nutrients.