herons, ibis and the wood stork (Heald et 

 al. 1974). 



7.2 RIVERINE FORESTS 



Tidal streams and rivers, fringed 

 largely by red mangroves, connect the 

 freshwater marshes of south Florida with 

 the shallow estuarine bays and lagoons 

 (Figure 12). Few of these streams have 

 been studied thoroughly. The exception is 

 the North River which flows into White- 

 water Bay and was studied by Tabb (1966) 

 and Odum (1970). Springer and Woodburn 

 (1960) collected fishes in a bayou or 

 tidal pass connecting Boca Ciega Bay and 

 Old Tampa Bay. Carter et al. (1973) 

 reported on the fishes of two tidal 

 streams entering Fahkahatchee and Fahka 

 Union Bays. Nugent (1970) sampled fishes 

 in two streams on the western shore of 

 Biscayne Bay. Characteristics of these 

 areas and sampling gear used by the inves- 

 tigators are summarized in Appendix A. 



These tidal streams and associated 

 riverine mangrove forests exhibit extreme 

 seasonal variability in both physical 

 characteristics and fish community compo- 

 sition. Salinity variations are directly 

 related to changes in the make-up of the 

 fish assemblage. During the wet season 

 (June - November), salinities fall 

 throughout the water courses and, at some 

 locations in certain heavy runoff years, 

 become fresh all of the way to the mouth 

 (Odum 1970). Opportunistic freshwater 

 species, which are normally restricted to 

 the sawgrass and black needle rush marshes 

 of the headwaters, invade the mangrove 

 zone. These include the Florida gar, 

 Lepi sosteus pi a ty r h i nc us ; several 

 centrarchid sunfishes of the genus Lepomis 

 and the largemouth bass, Micropterus 

 sal moi des ; the freshwater catfishes, 

 Ictalurus natalis and Noturus gyrinus; and 

 the killifishes normally considered 

 freshwater inhabitants such as Lucani a 

 goodei and Ri vulus marmoratus. 



During the dry season (December to 

 early May) salinities rise as a result of 

 decreased freshwater runoff and continuing 

 evaporation. Marine species invade the 



tidal streams primarily on feeding forays. 

 Examples include the jewfish, Epinephelus 

 ita jara , the stingrays (Dasyatidae), the 

 needlefishes (Belonidae), the jacks 

 (Carangidae), and the barracuda, Sphyraena 

 barracuda . Other seasonal movements of 

 fishes appear to be temperature related. 

 Tabb and Manning (1961) documented move- 

 ments of a number of species from shallow 

 inshore waters to deeper water during 

 times of low temperature stress. The 

 lined sole, the hogchoker, the bighead 

 searobin, and the striped mullet, for 

 example, are much less frequently caught 

 in winter in shallow inshore waters. 



A third type of seasonality of fish 

 populations in the tidal rivers is related 

 to life cycles. Many of the fish which 

 utilize the tidal stream habitat do so 

 only as juveniles. Thus, there are peaks 

 of abundance of these species following 

 offshore spawning when larval or juvenile 

 forms are recruited to the mangrove stream 

 habitat. In general, recruitment occurs 

 in the late spring or early summer fol- 

 lowing late winter and spring spawning 

 offshore or in tidal passes (Reid 1954). 

 Numerous species are involved in this life 

 cycle phenomenon including striped mullet, 

 grey snapper, sheepshead, spotted sea 

 trout, red drum, and silver perch. 



The only estimate of fish standing 

 crop from tidal stream habitats is that of 

 Carter et al. (1973). They recorded 27 

 species weighing 65,891 g (wet wt.) from 

 an area of 734 m or about 90 g/m . This 

 is probably an overestimate since an un- 

 known portion of the fish community had 

 moved from the flooded lowlands to the 

 stream on the ebb tide; sampling occurred 

 at low tide in October. Nonetheless, this 

 is an indication of the high fish standing 

 crop which this mangrove-associated habi- 

 tat can support. The number of species 

 reported from individual tidal streams 

 annually ranges from 47 to 60 and the 

 total from all tidal streams in southwest 

 Florida is 111 species (Appendix B). 



The food webs in these riverine man- 

 grove ecosystems appear to be predomi- 

 nantly mangrove detritus-based, although 

 the Biscayne Bay stream studied by Nugent 



52 



