The St. Marks and Wakulla marshes are two undisturbed Juncus tidal marshes located in northern Florida. A study of the seasonal fluctuations of temperature, salinity, numerical abundance, and biomass of fish in three tidal creeks at each locality provided data for community diversity
indices which were used to interpret the temporal changes in the compositions of fish communities. Species similarity between the samples collected from spatially separated creeks was examined with reference to tides and seasons employing the Homogeneity Index of Sanders. Salinity in the
creeks varied between 3.9 and 27.81‰, and temperature between 12° and 36°C. Although a total of 55 species was caught during the year, only seven cyprinodontiform species, Menidia beryllina, Leiostomus xanthurus, Eucinostomus argenteus, and Anchoa mitchilli proved
to be the dominant species based on Sanders' Biological Index. Also, a difference in the Community composition in relation to tides was observed. The name Fundulus-Menidia community is proposed for fish populations of north Florida marshes. The average numerical abundance and biomass
were greater at low tides. Neither type of overall abundance was correlated with seasonal temperature or salinity. However, temperature showed a negative correlation with the abundance of L. Xanthurus, and a positive correlation with cyprinodontiform species. Salinity showed a positive
correlation with the recruitment of L. xanthurus and Lagodon rhomboides. This explains their abundance in certain seasons. The species of fish were grouped into permanent residents, species utilizing marshes as nursery, foraging species, and sporadic visitors. The criteria
for such determination were gut contents, occurrence at low or high tides, and monthly length frequencies. Most of the species were represented by juveniles. A seasonal succession in the recruitment of juveniles of different species was observed. Diversity Index showed an increase with
the onset of warmer temperature. This index was influenced both by species richness and equitability of distribution of the individuals of component species. Statistical tests showed significant seasonal variations of H′ and E. In cooler months a few species made up the bulk of the catches,
while in warmer months a greater number of species showed more equitable distribution of their individuals. The three tidal creeks showed low species similarity in relation to tides and seasons at St. Marks, and higher similarity at Wakulla. This is probably due to the proximity of Wakulla
marsh to the open Apalachee Bay.
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