crops and the greatest species richness of 

 fishes occur in the late summer and early 

 fall (Clark 1970). Fish densities decline 

 in the autumn and winter as many fishes 

 move to deeper waters. 



7.4 FRINGING FORESTS ALONG OCEANIC BAYS 

 AND LAGOONS 



Mangrove-fringed "oceanic" bays and 

 lagoons are exemplified by Porpoise Lake 

 in eastern Florida Bay (Hudson et al. 

 1970), western Florida Bay (Schmidt 1979), 

 southern Biscayne Bay (Bader and Roessler 

 1971), and Old Rhodes Key Lagoon in 

 eastern Biscayne Bay (Holm 1977). Charac- 

 teristics of these sites are summarized in 

 Appendix A. Compared to the mangrove- 

 fringed bays discussed in the previous 

 section, these environments generally ex- 

 hibit clearer water, sandier substrates, 

 and higher and less variable salinities. 

 Closer proximity to the Florida reef 

 tract, the Atlantic Ocean, and the Gulf of 

 Mexico results in a larger potential pool 

 of fish species. These four locations 

 have produced reports of 156 fish species 

 (Appendix B). 



Mangrove fringes make up a relatively 

 small proportion of these environments; 

 accordingly, their contribution to the bay 

 food webs is probably not very large. 

 Bader and Roessler (1972) estimated that 

 the fringing mangrove community contrib- 

 utes approximately 1% of the total energy 

 budget of southern Biscayne Bay; they 

 considered only mainland mangroves and did 

 not include the small area of mangrove 

 islands. The main ecological role of the 

 fringing mangroves in this type of en- 

 vironment is probably twofold. First, 

 they increase the habitat diversity within 

 an otherwise relatively homogeneous bay 

 system. Second, they provide a relatively 

 protected habitat for juvenile fishes (and 

 certain invertebrates) that later move to 

 more open water or coral reef communities. 

 The second role is analogous to one of the 

 ecological roles of sea grass communities 

 (see Zieman, in prep.) although the fish 

 species involved may be different. 



Based primarily on habitat designa- 

 tions of Voss et al. (1969), the fishes of 

 Biscayne Bay can be characterized as to 

 preferred habitat. Of the three main 

 habitat types, (1) rock/coral/seawall, (2) 

 grassbed/tidal flat, and (3) mangrove, the 

 grassbed/tidal flat ranked first in fish 

 species occurrences. One hundred and 

 twenty-two of 156 species (79%) are known 

 to occur in this environment. 

 Rock/coral /seawal 1 habitats were fre- 

 quented by 49 species (32%) and mangroves 

 are known to be utilized by 54 species 

 (35%) of the total fish species recorded 

 from this bay. 



7.5 OVERWASH MANGROVE ISLANDS 



In terms of fish-related research, 

 these communities are the least studied of 

 all mangrove community types in south 

 Florida. They are typified by the low- 

 lying mangrove-covered islands that occur 

 in the Florida Keys and Florida Bay and 

 may be overwashed periodically by the 

 tides. Examples include Shell Key, Cotton 

 Key, and the Cowpens. Islands of this 

 type extend southwest from the Florida 

 mainland through the Marquesas. The Dry 

 Tortugas lack well -developed mangrove com- 

 munities although stunted trees are found 

 (Davis 1942). 



These islands are the most oceanic of 

 any of the mangrove communities discussed. 

 They are characterized by relatively clear 

 water (Gore 1977) and are largely free of 

 the freshwater inflow and salinity varia- 

 tions which characterize other Florida 

 mangrove communities to varying degrees. 

 Numerous statements exist in the litera- 

 ture acknowledging the frequent proximity 

 of mangrove islands to coral reefs and sea 

 grass beds (McCoy and Heck 1976; Thayer et 

 al. 1978). Olsen et al. (1973) workinq in 

 the U.S. Virgin Islands, found 74% to 93% 

 overlap in the fish species composition of 

 fringing coral reefs and shallow mangrove- 

 fringed oceanic bays. Voss et al. (1969) 

 listed fish species that were collected 

 from all three types of communities: 

 fringing mangroves, coral reefs and sea 



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