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MEPS prepress abstract   -  DOI:

Predator density, not structure, influences intraspecific competition in the mud crab Dyspanopeus sayi

Rebecca E. Kulp*, Alyson V. Lowell, Nicolas J. Floros, Bradley J. Peterson

*Corresponding author:

ABSTRACT: Structured habitats can offer prey refuge by reducing the encounter rates between predator and prey. However, structured habitats can also reduce predator–predator encounters, thereby dampening intraspecific interactions and increasing overall prey consumption. In this study, we tested whether intraspecific competition among Sayi mud crabs Dyspanopeus sayi foraging on mussel (Mytilus edulis) prey was modified by the density of mimicked eelgrass (Zostera marina) shoots. Predation was measured in three predator densities (1, 3, or 6 predators) and 1 of 5 levels of shoot density. We found no impact of Z. marina on the intraspecific competition, regardless of predator density. Intraspecific competition was weak; per capita crab consumption decreased as predator density increased, and become significantly reduced when predator density increased from 1 to 6. However, there was no evidence of non-additive predator density effects when predator abundance doubled from 3 to 6 predators. Our results also indicate that eelgrass structure may not offer the sessile prey, M. edulis, refuge when one or more D. sayi predators are present. Further exploration needs to be completed to understand whether the lack of a structure effect is due to using a sessile prey opposed to a mobile prey, as used in other studies.