Effects of sea stars and crabs on sea scallop Placopecten magellanicus recruitment inthe Mid-Atlantic Bight (USA)

Abstract

Relationships between recruitment of the Atlantic sea scallop Placopecten magellanicus and the abundances of 3 types of invertebrate predators, the sand star Astropecten americanus, the common sea stars Asterias spp. and the crabs Cancer spp., were investigated using data from large-scale scallop surveys in the Mid-Atlantic Bight (USA). Both asteroid groups appeared to reduce sea scallop recruitment, with significantly lower recruitment in areas where the sea stars were in high abundance. No significant effect of Cancer spp. crabs on scallop recruitment was detected. Very high densities of A. americanus, no sea scallop recruitment, and low Asterias spp. densities were observed in all stations with depths > 85 m, and in many stations between 65 and 85 m. Astropecten americanus may be a dominant component of the deep-water (> 75 m) benthic community in the Mid-Atlantic Bight that is capable of excluding both sea scallops and Asterias spp. from areas where A. americanus are highly abundant.

Post-settlement predation by sea stars and crabs on the sea scallop in the Mid-Atlantic Bight

“…Thus, such high densities of A. americanus would certainly be capable of consuming the majority of scallop recruits in their area. Our results and the spatial distribution of A. americanus further support the assertion by Hart (2006) that predation by A. americanus may functionally ex clude sea scallops from the deeper depths of the Mid-Atlantic Bight.…”

“…During their pre-and early post-settlement period, they are subject to multiple sources of mortality that influence their abundance and spatial distribution. Post-settlement mortality rates among juvenile sea scallops are high, mainly due to sea star and crab predators, but their natural mortality declines as the scallops grow (Elner & Jamieson 1979, Barbeau & Scheibling 1994, Stokesbury & Himmelman 1995, Hart 2006. We hypothesize that these predators are influencing the spatial distribution and temporal dynamics of scallop recruitment in the MAB.…”

“…The sea star Astropecten americanus is abundant in the middle and outer continental shelf of the MAB and is the dominant asteroid on the outer shelf (Boesch 1979, Franz et al 1981, Hart 2006. Their upper depth limit decreases from 25 m at their southern limit off Cape Hatteras to 150 m at its northern limit on Georges Bank; their geographic range is limited by summer thermal stress in the south and winter thermal stress in the north (Franz et al 1981).…”

“…The third predator group consists of Cancer crabs (C. irroratus and C. borealis), which are found throughout the MAB (Hart 2006). They are visual predators capable of rapidly depleting juvenile sea scallops and can be a significant source of scallop mortality (Elner & Jamieson 1979.…”

Mortality of sea scallops Placopecten magellanicus in the Mid-Atlantic Bight: Comment on Stokesbury et al. (2011)

“…In highly fecund marine organisms such as sea scallops, mortality is very high during their larval and post-settlement juvenile stages (McGarvey et al 1992, Gosselin & Qian 1997, Hart 2006. Non-linear, rapidly saturating relationships between egg production and recruitment, as observed in sea scallops and many other marine species, indicate that there is strong intra-cohort density-dependent mortality at these early life-history stages (Shepherd & Cushing 1980, NEFSC 2010.…”