Effects of three different macrophytic covers and the presence of alternative prey on survival of grass shrimp (Palaemonetes pugio and P. vulgaris) subjected to predation by killifish (Fundulus heteroclitus) were studied in the laboratory. Overall, survival of P. vulgaris was significantly greater (82%) than that of P. pugio (70%). This difference in survival was attributed to the greater tendency of P. pugio to swim outside the covers, making it more vulnerable to predation. Both prey species responded similarly to the different cover conditions. Survival without cover (gravel substrate) was 48%. In cover provided by a plastic plant made to resemble Ambulia, 75% of the starting population survived. In cover furnished by field-collected specimens of the flat chlorophyte, Ulva, survival was 71%, compared to 98% survival in the branched green alga, Codium. Predation pressure on neither species was significantly enhanced or diminished by the presence of a second prey species.
For both grass shrimp species, increased survival in Codium in the presence of the predator was attributed to the physically more complex nature of this macrophytic cover.