The general development of the 

 mixed (continental and insular) fish 

 fauna of the Florida reefs is sum- 

 marized by Starck (1968) as follows: 



"During the last glacial period 

 tropical marine species were re- 

 stricted to a much narrower latitu- 

 dinal area and the Florida shore 

 fauna was predominantly temperate in 

 nature (Walters and Robins 1961). 

 The present reef fish fauna consists 

 of relatively recent immigrants that 

 have crossed the Florida Current 

 from the West Indies or drifted with 

 it from the Yucatan peninsula. This 

 barrier has apparently been effec- 

 tive only for forms with very limit- 

 ed swimming powers as adults and 

 with reduced or absent planktonic 

 larval periods. This category 



includes the speciose gobies and 

 blennies. Certain other forms while 

 able to cross the Straits have been 

 unable to develop normal populations 

 due to local conditions. 



"Two factors are readily appar- 

 ent which might adversely affect 

 some West Indian reef species in 

 Florida. One is an unusually high 

 degree of siltation for a coral reef 

 area and the other is a surprisingly 

 dense population of many species on 

 the Florida reefs perhaps creating 

 an unfavorable competitive situation 

 for some other species." 



The mahogany snapper ( Lutjanus 

 mahoqani ) is an example of a species 

 occurring in the Florida reef tract, 

 for which local conditions are ap- 

 parently unfavorable. Thresher 

 (1977) and Zieman (1982) examine in 

 greater detail the implications of 

 the two factors (siltation and spe- 

 cies density) on population dynamics 

 in Florida's marine environment. 



In spite of the environmental 

 and physical (Florida Current) 

 barriers, the Florida Keys offer a 



quite favorable environment for fish 

 productivity. The combination of 

 favorable water temperatures, the 

 variety and abundance of foods 

 (pelagic, planktonic and nearshore 

 detrital) and the variety of nursery 

 grounds and habitats results in as 

 rich a fish fauna as found anywhere 

 in the Western Atlantic (Zieman 

 1982). 



Two distinct patterns of noc- 

 turnal and diurnal behavior are 

 exhibited by the Florida Keys fish 

 fauna. This has historically led 

 surveyors of the marine fauna to 

 underestimate and occasionally mis- 

 judge the species composition and 

 behavior of many of the reef tract's 

 inhabitants (Starck and Davis 1966, 

 Gilbert 1972). Starck and Davis 

 (1966) examined both night and day 

 species composition and behavior for 

 the region around and including 

 Alligator Reef. The following is a 

 summary of their observations. 



The fish fauna of the reef 

 tract fall into three groups based 

 on feeding and activity: nocturnal, 

 diurnal, and crepuscular. The lat- 

 ter group refers to the fish active 

 in the twilight or dusk and dawn 

 hours. 



The herbivorous families, sea 

 chubs (Kyphosidae), parrotfish 

 (Scaridae), surgeonfish (Acanthur- 

 idae) , and certain members of the 

 damselfish (Pomacentridae) , clinids 

 (Clinidae), and combtooth blennies 

 (Blenniidae) are apparently truly 

 diurnal. Their noctural behavior is 

 at best alert but inactive, as with 

 the surgeonfish. 



Omnivores of the halfbeak (Hem- 

 iramphidae), angel and butterflyfish 

 (Chaetodontidae) , trigger and file- 

 fish (Balistidae), and trunkfish 

 (Ostraciidae) families feed in the 

 day. At night their habits vary 



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