Seasonal wetland hydrology drives predator and prey co-occurrence in a subtropical estuary: Implications for predator-prey interactions and trophic dynamics

Background/Question/Methods

The species composition of ecological communities reflects interactions among organisms as well as between organisms & the abiotic landscape they experience. At small spatial and temporal scales, abiotic conditions influence patterns of species movement and habitat use.  At larger scales, abiotic factors affect patterns of species abundance and distribution. Abiotic parameters also influence the strength and outcome of species interactions, with consequences across multiple ecological scales. The structuring effect of abiotic conditions may be particularly important along ecotonal habitats. In the southwestern Everglades, mangrove-lined creeks link freshwater marshes to estuarine habitats. In this study examined the spatiotemporal dynamics of fish communities along the upper Shark River in Everglades National Park, where conditions are oligohaline to mesohaline. Ten sites in the tidal creeks were sampled during the wet, early-dry, and mid-dry seasons of 2004-20119, utilizing electrofishing as a primary sampling methods. In particular, we focused on the response of different functional groups to seasonal hydrological conditions (e.g., marsh water levels and salinity).

 Results/Conclusions

Our results show that fish abundance varies markedly yearly and seasonally in response to hydrological conditions, but functional groups are affected differently. Marsh fishes move into estuary in the dry season, locally increasing prey and predator abundance, but limited to the upper estuary, perhaps by salinity. Marine and estuarine predators seem to move to the upper estuary matching increases in freshwater prey, but appear limited by oxygen conditions. Freshwater prey taxa make large contributions to the prey base in the dry season, and their abundance is negatively related to marsh water levels. The data indicate that ecotonal creeks may serve as important dry-season refugia for freshwater taxa, and that pulses of freshwater taxa into tidal creeks may trophically link estuarine and marsh habitats. Furthermore, the nature and strength of these linkages appear to be affected by how species and functional groups respond spatially and temporally to abiotic conditions. Increases in freshwater inflows related to restoration efforts may affect this linkage by prolonging the pooling of freshwater in upland marshes and changing abiotic conditions at the ecotone.