Figure 17. Snail grazing on the tip of an encrusted Thalassia leaf. Small snails and 

 hermit crabs are frequently seen grazing the heavily epiphytized portions of seagrass 

 leaves. 



Roessler and Tabb 1974; Bader and Roessler 

 1971; Tabb et al . 1962; Tabb and Manning 

 1961). Faunal differences among studies 

 reflect sampling gear selectivity, but 

 typically penaeid and caridean shrimp are 

 less numerous than the smaller macrocrus- 

 taceans (i.e. amphipods, isopods), yet 

 represent a larger biomass within the bed. 

 For example, data from Brook (1977) for a 

 Card Sound turtle grass grass bed indi- 

 cated that amphipods and caridean shrimp 

 represent respectively 5.8% and 23.3% of 

 estimated biomass of principal taxa col- 

 lected and 12.4% and 50,3% of crustacean 

 biomass. Demonstrating the importance of 

 the physical structure of the grass car- 

 pet. Yokel (1975a) reported that the 

 standing crop of crustaceans (estimated 

 using a travel) was 3.9 times larger in 

 mixed seagrass and algal flats than on 

 nearby unvegetated bottoms (see Figure 

 18). 



It is a long standing assumption that 

 the grass carpet represents protection 

 from predation for the animals living in 

 it. The dense seagrass blades and rhizomes 

 associated with the grass carpet provide 

 cover for invertebrates and small fishes 

 while also interfering with the feeding 

 efficiency of their potential predators. 

 Experimental evidence suggests that grass 

 bed invertebrates actively select vege- 

 tated habitat rather than bare sand indi- 

 cating that habitat preference is an 

 important force contributing to observed 

 faunal densities in grass beds (Heck and 

 Orth 1980). Selection appears to be based 

 on the form or structural characteristics 

 of the seagrass (Stoner 1980a). 



It is speculated from experimental 

 work using shapes that the caridean 

 shrimp, Hippolyte cal iforniensis , locates 

 its host plant, Zostera marina , visually 



48 



