Aquatic-terrestrial linkages in the Florida Everglades: Evidence and prospective investigations

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Alan J. Mock and Peter J. Flood, Biological Sciences, Florida International University, North Miami, FL, William F. Loftus, Aquatic Research & Communication, LLC, Vero Beach, FL, Joel C. Trexler, Biological Science, Florida State University, St. Teresa, FL

Background/Question/Methods
The transfer of energy and nutrients across aquatic and terrestrial ecosystems can subsidize food webs and enhance productivity in recipient systems. The importance of resource subsidies is dependent on quantity, quality, timing, and vector of material transfer in relation to background concentrations. Although these linkages are well described between permanent bodies of water and adjacent riparian habitats, they remain poorly understood in ephemeral wetlands. The Florida Everglades is a large oligotrophic wetland with pronounced wet and dry seasons that limit habitat available for aquatic organisms. Here, we provide data on the use of terrestrial subsidies among aquatic consumers and infer how the importance of this subsidy is dependent on season and habitat. The aquatic community was sampled during wet and dry seasons from three distinct habitats: alligator ponds, spikerush marshes, and sawgrass marshes. Diet items were identified through stomach-content analysis. We determined taxa that rely on terrestrial diet items and calculated the mean proportion of terrestrial diet items in consumer diets for both the whole community and species size classes within habitat-season levels. Furthermore, we analyzed differences in terrestrial prey subsidies among habitat-season levels using permutate ANOVA with post-hoc pairwise permutation tests when appropriate.
Results/Conclusions
Thirteen species (16 species size classes) consumed terrestrial prey items (Aranae and Hymenoptera). Hymenopterans never accounted for more than 5% of the diet for a species size class at any habitat-season level. Conversely, Aranae exceeded 5% in 9 species size classes across habitat-season levels with a maximum of 18% (Golden Topminnow - Fundulus chrysotus, dry-season pond). Additionally, permutated ANOVA resulted in a significant difference in the number of Aranae in consumers diets among habitat-season levels, but not in the number of Hymenopterans. Pairwise permutation tests for Aranae among habitat-season levels resulted in 10 of 15 comparisons being significant. Dry-season pond and dry-season sawgrass marsh consumers had the most Aranae in their diets, while dry-season spikerush consumers had the least. Between seasons, the mean number of Aranae per stomach differed by a factor of 2-3 depending on habitat. These findings highlight the need to better understand the importance of aquatic-terrestrial linkages in wetland habitats. To do this, we provide descriptions of two prospective investigations: one that seeks to understand how community composition influences the production of emerging aquatic insects, and another that will investigate how subsidy pathway influences the quality and mercury bioaccumulation of terrestrial consumers.