RECOVER MAP 3.1.4.7 Role of Marsh-Mangrove Interface Habitats as Aquatic Refuges for Wetland Fishes and other Aquatic Animals

Work conducted in 2008 will continue to establish baseline conditions for fish and macroinvertebrate communities in the mangrove creeks of Everglades National Park (ENP). This monitoring was begun in 2004, with the focus from 2004-2007 on testing methodologies and strategies for sampling fishes and macroinvertebrates in this difficult to-sample mangrove habitat. Findings from the 2004-2007 work showed electrofishing catch per unit effort (CPUE) provided a reliable estimator of large-bodied fish abundance and species richness at salinities below 15 (Loftus and Rehage 2007, Rehage and Loftus 2007). For the smaller species, our data showed that minnow trap CPUE provides an adequate estimate of forage-fish and macroinvertebrate abundance in the mangrove prop-root microhabitat. Results also showed that there is significant biotic connectivity between freshwater marshes and the oligohaline/mesohaline mangrove habitats, particularly along the Shark Slough-Shark River ecotone. These data indicate that mangrove creeks serve as important dry-season habitat for a variety of freshwater taxa. As upstream marshes dry, fishes and decapods move into mangrove creeks. We hypothesize that the timing and spatial extent of this movement into creeks is affected by the pattern and timing of water recession in marshes, and the effects of this recession on salinity levels in the creeks. We suspect that animal movements into creeks results in a shift in energy flow from avian predators in the wetlands to piscine predators in the creeks. Ecotonal creeks are deep (> 1m), and prey that move into creeks become unavailable to many wading birds, instead serving as prey for freshwater, estuarine, and marine fish predators (along with alligators). In 2008, we continue to test these hypotheses. Sampling in FY08 will result in additional sampling events and increase replication, which should enhance our ability to detect changes in the fish and macroinvertebrate community in relation to changes in key ecological drivers, namely freshwater inflow and salinity. In particular, our objectives for 2008 include:
(1) Continue data collection begun in 2004 to provide pre-CERP baseline conditions for the fish and macroinvertebrate community inhabiting mangrove creeks;
(2) Relate patterns of variation in the fish and macroinvertebrate community of creeks to key hydrological and physiochemical variables;
(3) Continue to develop an integrated experimental design that will optimize effort and information utility, incorporating both spatial (across the landscape) and temporal (seasonal and interannual) variability;
(4) Continue to work with other PIs to integrate our results with theirs in testing the key hypotheses in MAP II.
II. Statement of work (abbreviated)
This MAP activity will enhance the ongoing biological monitoring in freshwater and estuarine regions of ENP by providing data from an infrequently sampled habitat that provides both a source and a sink for wetland forage fishes that are prey for wading birds. Relatively little is known about the fish community inhabiting mangrove creeks in ecotonal and estuarine regions of southwest Florida. Small-scale inventory studies in several creek systems showed a mixed assemblage of marine, estuarine, and freshwater fishes (Tabb and Manning 1961, Tabb et al. 1962, McPherson 1970, Odum 1971, Loftus and Kushlan 1987), but those studies are not recent and mostly provided inventory data. Without understanding the factors that control the survival and abundance of those fishes once they are confined to this dry-season habitat, it is impossible to predict the effects of CERP actions on this prey base in the future. Similarly, this activity also provides the only data for freshwater and estuarine fishes that support a valuable sport fishery in south Florida. Without these data on the effects of hydrology and salinity variation on patterns of fish abundance and diversity, the effects of CERP on those key fishery species will not be science-based.