The pinfish's predatory efficiency on 

 amphipods decreases with increasing den- 

 sity of Zoster a marina blades (Nelson 

 1979a). Coen Tl9T9l found in single- 

 species experiments (one shrimp species at 

 a time) that with increasing cover of red 

 algae ( Pi gen i a simplex , Laurencia spp., 

 Gracilaria spp. and others) the pinfish's 

 foraging efficiency on Palaemon floridanum 

 and Palaemonetes vulgaris was reduced. 

 The killifish ( Fundulus heterocl itus ) fed 

 less efficiently on the grass shrimp 

 ( Palaemonetes pugio ) in areas of densest 

 artificial seagrass. Virtually nothing is 

 known about the relation of typical grass 

 bed fishes and their predators; research 

 on this topic would be fruitful. 



5.4 REPTILES 



Although there are several species 

 of sea turtles in the Gulf of Mexico and 



Caribbean, the green sea turtle ( Chelonia 

 mydas ) is the only herbivorous sea turtle 

 (Figure 20). In the Caribbean, the main 

 food of the green turtles are sea grasses 

 and the preferred food is Thalassia , 

 hence the name turtle grass (see section 

 6.2). 



Green turtles were formerly abundant 

 throughout the region, but were hunted 

 extensively. Concern over the reduced 

 populations of green turtles dates back 

 to the previous century (Munroe 1897). 

 Although limited nesting occurs on the 

 small beaches of extreme south Florida, 

 the region has almost certainly been pri- 

 marily a feeding rather than a nesting 

 site. Turtle and manatee feeding behavior 

 are described in Chapter 6. 



The Ainerican crocodile ( Crocodylus 

 acutus ) occurs in the shallow water 

 of Florida Bay and the northern Keys. 



y 



Figure 20. Seagrass bed following grazing by green sea turtle. Note the short, evenly 

 clipped blades. The scraping on the Thalassia blade in the center is caused by the 

 small emerald green snail, Smaraqdia viridis . 



53 



