Studies on the Animal Communities in Two North Florida Salt Marshes

Part II. Macroinvertebrate Communities

Species composition and fluctuations of abundance of macroinvertebrates of two Juncus tidal marshes of north Florida were studied during 1973. Both the marshes were subdivided into low, upper, and high marsh zones based on the soil characteristics. In the low and upper marsh zones, random samples of epifauna were taken monthly with l-m² traps, and infauna from l0-cm deep and 0.0625-m² samples of soil. Samples were also obtained along two transects, including high marsh, at each locality to study the horizontal zonation of species in the three soil types. Tidal creeks were sampled monthly with a seine at low and high tides. Water temperature, salinity, and dissolved oxygen were measured.

A total of 51 species were encountered, and marsh zones exhibited distinct species assemblages. Based on Biological Index (BI) values, the lower and upper marsh were Littorina-Cyathura-tanaidacean communities with an abundance of three polychaetes, Scoloplos fragilis, Neanthes succinea, and Laeonereis culveri. High marsh zones were characterized by an abundance of Uca spp., Melampus bidentatus, and Cerithidea scalariformis. Data from l-m² areas along the two transects revealed a distinct horizontal zonation of species distribution.

The mean density of marsh invertebrates in trap samples was 475/m², and average densities were significantly higher in low marsh (540/m²) than in the upper marsh (38l/m²). Peaks of abundance were observed in winter and fall. Mean biomass for the year was 123g/m². Species Diversity (H′) was significantly different among seasons, with peaks in spring and fall. Species Richness (D), and Equitability (E) closely followed the seasonal trends of H′. Mean Homogeneity (HI) of species occurrence was 33% between the low and upper marsh zones.

Some species showed distinct seasonal succession. Based on length frequency data, some species were found to breed in the fall and winter.