The role abiotic factors play in structuring communities is one of the fundamental questions in ecology. 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. 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. This study examined the spatial and temporal dynamics of fish communities along oligohaline to mesohaline reaches of tidal creeks within the southwest region of Everglades National Park. Fifteen creeks were sampled in two drainages: Rookery Branch and North and Roberts rivers. Sampling was conducted during the wet, early-dry, and mid-dry seasons of 2004-2008, utilizing electrofishing, gill nets, and minnow traps.
Abundance and species composition differed between drainages and across seasons and years. Overall, fish abundances and catches were more diverse in Rookery Branch creeks, particularly during the drier sampling periods. This pattern reflected an influx of freshwater fishes into Rookery Branch as water levels upstream receded and marshes dried. Influxes of freshwater species were short-lived, particularly for smaller taxa, suggesting heavy predation once fish moved from upstream marshes into tidal creeks. Our results indicate head-water creeks may serve as important dry-season refugia for freshwater taxa, and that pulses of freshwater taxa into tidal creeks may also increase seasonal foraging opportunities for transient oligohaline and mesohaline species. Restoration and recovery of historic freshwater inflow within the Everglades ecosystem may reverse this trend, prolonging the pooling of freshwater in upland marshes. Our results suggest under expanded oligohaline conditions, pulses of smaller fishes into creeks may be expected to decrease, thus increasing forage biomass for numerous avian predators.