Grass shrimp Palaemonetes pugio predation on sediment- and stem-dwelling meiofauna: field and laboratory experiments

Field and laboratory experiments were conducted to clarify the predatory ro le of Palaemonetes pugio Holthius in salt-marsh benthic communities. Field experiments (cage enclosures using P. pugio as a predator) were conducted o n unvegetated mudflat and vegetated-marsh sites. Neither sediment- or stem- dwelling meiofaunal abundances were significantly impacted. Laboratory expe riments measured the functional response of P, pugio feeding on suspended h arpacticoid copepods, tested the efficiency of P, pugio feeding on harpacti coids in sediments, and measured the predation rate of P. pugio on stem-dwe lling meiofauna. Grass shrimp feeding rate on suspended copepods followed a type II functional response, increasing with increasing prey density to a maximum of 59 copepods h(-1). When a sediment refuge was available, a 40% d ecline in the consumption of copepods by P. pugio was noted; this decreased feeding efficiency may contribute to the lack of significant declines in m eiofaunal abundances in field enclosures over unvegetated sediment. P. pugi o proved to be a highly effective predator on the fauna of Spartina alterni flora stems, significantly reducing abundances of stem-associated meiofauna within 24 h and consuming an estimated 35 meiofauna h(-1). The greatest im pact was exhibited on the lowest (0 to 6 cm) portion of the stems. These ex periments suggest that laboratory experiments are an important aid to help interpret field experiments examining predation on meiofauna, and that Spar tina stems, and their epiphytic algae and meiofauna, are important, but lar gely overlooked, resources in salt-marsh food webs.