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Field and laboratory experiments were conducted to clarify the predatory role of Palaemonetes pugio Holthius in salt-marsh benthic communities. Field experiments (cage enclosures using P. pugio as a predator) were conducted on unvegetated mudflat and vegetated-marsh sites. Neither sediment- or stem-dwelling meiofaunal abundances were significantly impacted. Laboratory experiments measured the functional response of P. pugio feeding on suspended harpacticoid copepods, tested the efficiency of P. pugio feeding on harpacticoids in sediments, and measured the predation rate of P. pugio on stem-dwelling 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% decline in the consumption of copepods by P. pugio was noted; this decreased feeding efficiency may contribute to the lack of significant declines in meiofaunal abundances in field enclosures over unvegetated sediment. P. pugio proved to be a highly effective predator on the fauna of Spartina alterniflora stems, significantly reducing abundances of stem-associated meiofauna within 24 h and consuming an estimated 35 meiofauna h-1. The greatest impact was exhibited on the lowest (0 to 6 cm) portion of the stems. These experiments suggest that laboratory experiments are an important aid to help interpret field experiments examining predation on meiofauna, and that Spartina stems, and their epiphytic algae and meiofauna, are important, but largely overlooked, resources in salt-marsh food webs.

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Marine Ecology Progress Series

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