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 sitesbut they were surprised at the magnitude of the difference and the extent to which it occurred.
"The rate of daily seagrass growth ranged from 37 square millimeters at large reefs to 10 square millimeters at control sitesnearly a four-fold difference," Allgeier said. "Fish are putting an enormous amount of nutrients into this systemit appears to be even more than all other sources, including runoff from golf courses and all other human caused impacts, combined."
The effect extended for roughly three meters around each large reef. The fish were contributing more nutrients than the seagrass could take in, allowing the excess nutrients to drift further away from their source, fertilizing seagrass and algae in ever-widening areas. The researchers anticipate this effect to extend further with increased time.
Allgeier described the large reefs as "biogeochemical hotspots"areas with particularly high rates of chemicals cycling between organisms and the environment.
"The reefs are nodes within the ecosystem matrix," he said. "They're increasing productivity around the reefs by orders of magnitude. If there are enough of them (reefs), then they may be increasing productivity at the ecosystem level by orders of magnitude as well. That's something we're going to be looking at next."
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.
"Even if you have large numbers of fish, if they're dominated by one species, they're filling just one nutrient cycling niche in that ecosystem," he said. "That's not how these systems are used to being fed nutrients."'/>"/>
|Contact: Jacob Allgeier|
University of Georgia