Effects of habitat on reproduction of the bay scallop, Argopecten irradians

Habitat suitability indices explain the relationship between various environmental factors and either the presence or abundance of a species.  However, even though an organism may be present at a site, that location may be a sink rather than a source for that species. Furthermore, an animal may be absent from a suitable site due to historical factors or migratory barriers.  In order to assess the importance of a habitat to an organism, one needs to link habitat characteristics to life history parameters.  In 2006 we conducted an experiment in Ninigret Pond, RI, USA to examine the relationship between habitat, survivorship and fecundity of the bay scallop, Argopecten irradians.  Mature scallops were caged at 14 sites differing in depth, salinity, temperature, vegetation type and cover, and sediment type.  At the peak of spawning season (late June to early July), scallops were collected, and somatic and gonadal mass measured.  Scallops at many sites experienced mortality after strong rains, although some scallops spawned before dying.  Surviving scallops occupied well-flushed sites 0.46 – 1.25 m deep with sandy sediment, no eelgrass, and algal cover ranging from 0-100%.  Scallops at different sites spawned at different times and differed in pattern of sperm vs. egg release.  Gonad mass/total mass was negatively correlated with eelgrass density.  This may reflect lower reproductive allocation or earlier spawning in eelgrass habitat.  Identifying the optimum habitat for scallop reproduction will aid managers in deciding where to focus restoration efforts.