Hypothesis 1: Freshwater delivery influences the importance of detritus to freshwater marsh and mangrove estuary food webs.
Approach - We propose to address this question in two ways. First, we will conduct experiments in Everglades wetlands to determine how energy-flow pathways are changed by freshwater delivery, particularly if the delivery is associated with P-enrichment. We will manipulate nutrients and key consumers using established in-situ field enclosures to test how freshwater sources and predator behaviors control markers of food assimilation (stable isotopes of C and N, fatty acids), delineating predictions based on the presence of key microbial energy-flow routes in oligotrophic Everglades wetlands that are changed when P is enriched. We will focus particularly on microinvertebrates, as our preliminary work has shown that rotifers and protozoan grazers may be key consumers in a currently undocumented microbial loop. The relevance of our experimental results will be explored in the context of our ongoing spatial studies documenting metazoan abundance along hydrological gradients and across seasons in the Everglades. Our second line of work will evaluate microbial energy flow into estuarine food webs, relying on movement studies to identify wide ranging estuarine consumers that travel between marshes, the ecotone, and downstream marine areas. After identifying foraging and "refuging" sites where consumers feed and travel to, we will evaluate isotopic and fatty acid signatures of detritus, algae, microinvertebrates, and mesoconsumers in an effort to delineate linkages to the wide-ranging top predators (i.e., alligators and large fish).
Variability in freshwater inflows will interact with SLR to modify the spatial scale of consumer-mediated habitat links.
Approach - To quantify the precise extent of animal movements and foraging behavior relative to environmental fluctuations, we will deploy satellite tags and animal-borne cameras. To determine variability in potential contributions of top predators to community dynamics and nutrient cycling, we will maintain quarterly sampling of bull shark abundance and bi-annual sampling of alligator abundance, diets, and body condition in the ecotone region in relation to freshwater flow, salinity, dissolved oxygen and nutrient concentrations, and other continuous FCE data. We will connect top predator abundance, foraging, and movement to mesoconsumer community dynamics by maintaining our seasonal electrofishing (wet, dry, and transition seasons), and determine connectivity between top and meso-consumers by complementing our abundance and tracking research with analyses of stomach contents, stable isotopes, and fatty acids. Resultant linkages will be interpreted relative to temporal variability in hydrologically-controlled environmental variables and in the context of microconsumer abundance and diets, described above. By conducting parallel research in a similarly oligotrophic mangrove estuary in Shark Bay, Australia, we will continue to improve our ability to generalize our findings about the importance of top predators in determining estuarine habitat connectivity in subtropical habitats. We will expand this comparative approach to include temperate estuaries through our coastal site collaborations in FCE III, particularly by synthesizing our findings with those of food web and consumer movement research conducted in parallel at the Plum Island Ecosystems LTER.