grass beds in Biscayne Bay, but there 

 appears to have been no systematic survey 

 of the fish assemblage characteristic of 

 the mangrove-covered or mangrove-fringed 

 Florida Keys. No one has quantified the 

 faunal connections which we hypothesize 

 exist between the mangroves and sea 

 grasses and between the mangroves and 

 coral reefs. 



In the absence of published data from 

 the mangrove key communities, only tenta- 

 tive statements can be made. In general, 

 we expect that while mangrove islands 

 serve as a nursery area for juvenile 

 fishes, this function is limited largely 

 to coral reef and marine inshore fishes 

 and not the estuarine-dependent species 

 that we have discussed previously. The 

 latter (juvenile snook, red drum, spotted 

 seatrout) appear to require relatively low 

 salinities not found in association with 

 most of the overwash islands. Casual 

 observation around the edges of these 

 islands suggests that characteristic 

 fishes include the sea bass family (Ser- 

 ranidae), t ri ggerf i shes (Bal istidae), 

 snappers (Lut jam' dae), grunts (Poma- 

 dasyidae), porgies (Span'dae) parrotfishes 

 (Scaridae), wrasses (Labridae), bonefishes 

 (Albulidae), jacks (Carangidae), damsel- 

 fishes (Pomacentridae), and surgeonf ishes 

 (Acanthuridae); many of these fishes occur 

 on or are associated with coral reefs. We 

 also suspect that considerable overlap 

 occurs in the fish assemblage of these 

 mangrove islands and sea grass communi- 

 ties; examples include puffers (Tetrao- 

 dontidae), pipefishes (Syngnathidae) , go- 

 bies (Gobiidae) and scorpionf ishes (Scor- 

 paenidae). Stark and Schroeder (1971) 

 suggested that juvenile gray snapper, 

 which use the fringing mangroves of the 

 keys as shelter during the day, forage in 

 adjacent sea grass beds at night. In the 

 absence of salinity barriers, predatory 

 fishes probably enter the fringes of these 



mangrove islands on the rising tide. 

 Included in this group are sharks, tarpon, 

 jacks, snook, bonefish and barracuda. 



7.6 GRADIENT OF MANGROVE COMMUNITY 

 INTERACTIONS 



Mangrove communities occur under a 

 wide range of conditions from virtually 

 freshwater at the headwaters of tidal 

 streams to nearly oceanic conditions in 

 the Florida Keys. Attempting to present a 

 single list of fish characteristic of 

 mangrove environments (Appendix B) can be 

 misleading. For this reason we presented 

 the concept of a continuum or complex 

 gradient in Figure 11 and have followed 

 that scheme throughout section 7. The 

 gradient stretches from seasonally fresh 

 to oceanic conditions, from highly varia- 

 ble salinities to nearly constant salini- 

 ty, from muddy and limestone substrates to 

 sandy substrates, from dark-stained and 

 sometimes turbid waters to clear waters, 

 and from food webs that are predominantly 

 mangrove detritus-based to food webs based 

 primarily on other energy sources. Clear- 

 ly, there are other gradients as one moves 

 from north to south in the State of 

 Florida. At the northern end of the 

 State, temperatures are more variable and 

 seasonally lower than in the south. Sedi- 

 ments change from predominantly silicious 

 in central and north Florida to predomi- 

 nantly carbonate in extreme south Florida. 

 Nevertheless, the complex gradient shown 

 in Figure 11, while greatly simplified for 

 graphic purposes, suggests that charac- 

 teristic fish assemblages replace one 

 another along a gradient of changing 

 physical and biogeographic conditions. 

 Such a concept is useful in understanding 

 the factors controlling the composition of 

 fish assemblages associated with mangroves 

 of the four major community types in south 

 Florida. 



57 



