Background/Question/Methods Both abiotic and biotic factors have been shown to influence the distribution and abundance of species in space and time.  In estuarine systems, salinity plays a key role in determining species abundance, community structure, and trophic dynamics.  In the southwest section of Everglades National Park (ENP), freshwater marshes transition to an expansive array of mangrove forests, islands, tidal bays, and creeks where salinity varies both seasonally and spatially throughout the estuary.  The estuary is inhabited by a diverse array of resident and transient fishes and macroinvertebrates, whose ecology is poorly understood.  In this study, we examined the distribution of palaemonid shrimp species (Caridea, Palaemonidae) throughout the Shark River estuary, ENP.  In particular, we examined the relationship among their seasonal abundance and distribution, salinity and other abiotic variables. Previous research has found salinity to be a primary force driving segregation among these shrimp, whereas other studies show biotic interactions, namely competition, strongly drive patterns of abundance and distribution.  To examine if these species played similar functional roles along the estuary, and if these species potentially competed for resources, we compared their stable δ¹³C and δ¹⁵N isotopic signatures.  Sampling was conducted with unbaited traps and repeated in the wet and dry seasons.
Results/Conclusions Five palaemonid species were found in our samples:  Palaemonetes paludosus, Palaemonetes pugio, Palaemonetes intermedius, Palaemon floridanus and Leander paulensis, with L. paulensis only collected during the wet season.  Overall, shrimp catches doubled in the dry season.  Catches at the upstream sites were dominated by P. paludosus, particularly in the wet season, while CPUE at the downstream most and higher-salinity sites were dominated by Palaemon floridanus, and L. paulensis in the wet season only.  Mid-estuary, multiple species co-occurred.  Preliminary δ¹⁵N analyses revealed that species likely play similar roles in the community.  δ¹³C values varied between sites, with upstream sites being more depleted compared to the downstream sites. These data suggests that changes in salinity regimes resulting from Everglades restoration may result in species replacement, with important implications for trophic dynamics.