The fish and crustacean faunas of tidally flooded fringing mangrove forests of Shark River contain representatives from regional freshwater, estuarine and marine species pools. We sample fishes and crustaceans bi-monthly using 2 X 3 m2 lift nets and 1 X 1.5 m blocking nets across the mouths of intertidal rivulets. These latter geomorphic structures are small drainages, approximately 0.5-0.75 m wide, and 20-30 cm lower than the adjacent forest floor. They flood earlier on the flood tide and hold water later on the ebb tide than the adjacent undissected forest floor.

The fishes entering the forest on a flood tide are uniformly small-bodied, probably due to relatively shallow flooding depths, at least when considered on a worldwide basis. Only a few families dominate the fauna. These include Fundulidae (killifishes), Gobiidae (gobies), Gerridae (gerrids), and Aplocheilidae (rivulins). The latter family contains only one species in North America, mangrove rivulus. This fish, whose physiology and behavior more closely resemble amphibians than other fishes, is being considered for listing as an endangered or threatened species. Nonetheless, it is common on the forest floor along the entire salinity gradient we sampled in Shark River.

Marsh and rainwater killifishes, inland silversides, mangrove rivulus and gerrids of the genus Eucinostomus dominate the fauna in the tidal fresh to oligohaline Tarpon Bay reach. The mesohaline site on the Harney River is flooded less deeply than other sites and is dominated by Eucinostomus and Rivulus. There are no species uniquely or characteristically present at the Harney River site. The site nearest the mouth of Shark River is polyhaline and shows the highest species richness. Eucinostomus and Rivulus are again abundant, but other species rarely captured further upriver are common here, i.e., frillfin and crested gobies, young-of-year gray snapper, and bay anchovies. We have captured three species of exotic fishes (walking catfish, pike killifish, Mayan cichlid) in relatively small numbers, and none to date at the most downstream site. This observation might indicate that the route of invasion is therefore from a freshwater rather than a marine source.

Amongst the decapod crustaceans, we tabulate only natant (swimming) forms as our lift and rivulet nets sample semi-terrestrial crabs poorly. The most common decapods are caridean shrimps of the genus Palaemonetes: at least three species are present. Considerably less common are blue crabs of the genus Callinectes.

Intertidal rivulet nets sample an unknown but considerably larger area than lift nets that sample 6 square meters. Perhaps not surprisingly, intertidal rivulet nets also contain consistently more species. It is possible, however, that this consistent pattern is also due to other factors. It is likely that these rivulet nets, situated directly on the forest/creek interface, capture species that use only the very fringe of the mangrove forest. In contrast, lift nets placed 9-16 meters into the forest are more likely to capture species that routinely penetrate further into the forest, and that make use of generally shallower waters than fishes taken in rivulet nets.

As sampling continues, we anticipate integrating biotic and physicochemical factors, defining patterns of temporal variability, and designing experiments to determine causal as opposed to strictly correlational relationships in the data. Further, we plan to extend the sampling to Lostmans River, to begin life history studies of the more abundant species, and to work with ATLSS modelers to begin parameterization of a mangrove fish model for the southwest coast. Such a model will be used to judge alternative restoration scenarios.

¹Carole, McIvor, U.S. Geological Survey, Florida Caribbean Science Center, Center for Coastal Geology and Regional Marine Studies, 600 Fourth Street South, St Petersburg, FL 33701, Phone: 727-803-8747, Ext 3022, Fax: 727-803-2032, Carole_McIvor@usgs.gov.

(This abstract was taken from the GEER Proceedings (PDF, 1.9 MB))

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