Consumer-driven nutrient cycling in marine ecosystems
Jake Allgeier measuring barracuda excretion
Artifical reef providing fish habitat
Consumer-driven nutrient cycling is now recognized as an essential component of ecosystem functioning in freshwater systems – my lab is one of the first to extend this research framework to marine environments. My lab’s research is describing how nearshore ecosystems of The Bahamas (my primary research location) are extremely oligotrophic, suggesting that nutrient cycling by marine organisms, namely fishes, may be a major vector of nutrient transport. Traditionally, seagrass beds have been viewed as a key link in supporting high densities of consumer fauna, but it may be equally plausible that, especially in oligotrophic systems, consumer-driven nutrient recycling is a necessary precondition for dense seagrass and macroalgae beds to develop in the first place. Loss of a critical vector for nutrient recycling may result in reduced primary production, which may affect fishery production through an indirect, bottom-up, mechanism. We have demonstrated that ecosystem fragmentation and over-exploitation of top predators do indeed have a drastic impact on the rate of nutrient supply to primary producers. This anthropogenically-induced reduction of nutrient recycling translates into altered primary producer nutrient limitation regimes, altered primary producer nutrient content and reduced growth rates of seagrasses. We are now mechanistically investigating these relationships using a series of artificial reefs constructed in shallow bays in The Bahamas. These artificial reefs will serve as one of our core experimental tools in the coming years, allowing for replicated, mechanistic tests of how human impacts may affect ecosystem function.