The Influence of Predatory Decapods, Refuge, and Microhabitat Selection on Seagrass Communities

This research was designed (1) to examine the role of predatory decapod crustaceans as an organizing force in prey distribution and abundance patterns, and (2) to compare the importance of vegetation as a prey refuge from predators with its importance as a microhabitat for epifauna in seagrass meadows. After documenting the predator—exclusion effectiveness of a new cage design by defaunating and monitoring faunal immigration into cages during a 2—mo period of high predator densities, I initiated a 1—mo manipulative field experiment designed to examine the refuge value of vegetation. Replicate predator—inclusion (treatment) and —exclusion (control) cages were established across a vegetation gradient in a Gulf of Mexico, USA, grassbed, and predator shrimp (Penaeus duorarum) were enclosed in treatment cages. While cages successfully excluded larger decapods and fishes, prey species had free access and rapidly colonized cages. A significant predation effect was detected for total densities of all major prey taxa in a simple (low plant biomass) habitat. The general consequence of increasing microhabitat structural complexity on the outcome of predator—prey interactions was a reduction in Penaeus effects on prey densities across the vegetation gradient. However, for some prey, predation effects remained relatively constant across this gradient. These results extend from the laboratory to nature the premise that seagrasses afford protection for certain epifauna. The experiments also reveal that macrophyte structural complexity can account for microhabitat distributions of some grassbed fauna without invoking differential predation as a causal mechanism. Strong nature association of epifauna with seagrasses and macroalgae appear to be net result of predation, refuge, and habitat selection.