Animals and natural cover types used in all experiments were collected from Indian River Bay, a small Atlantic estuary in southeast Delaware, U.S.A. This site was chosen because the sympatric grass shrimp species P. pugio and P. vulgaris, the killifish Fundulus heteroclitus, and natural plant covers (the green algae Codium fragile and Ulva lactuca) were easily found there. A dip net was used to collect both grass shrimp species. Killifish and submerged macrophytes were collected with a seine drawn over relatively flat areas of tidal creeks. Substrate items were removed from the top 2 cm of marsh surface with a shovel at low tide. At the time of collection, Ulva and Codium dominated benthic macrophytes within the sampling area, and both were collected by hand.All field collected animals, plants, and substrate materials were transported to the laboratory in separate plastic containers.