Abstract
Sea stars, Asterias spp., found in high densities in the Nantucket Lightship Closed Area (NLCA), are a primary predator of the Atlantic sea scallop Placopecten magellanicus. Sea stars could be a controlling factor of Atlantic sea scallop population growth and distribution by affecting recruitment through consumption of spat and juveniles. Sea star abundance in the NLCA declined during an abnormally warm winter in 2012 that coincided with the successful settlement of scallop spat from an extreme recruitment event. This single event more than doubled the estimated abundance of the entire U.S. scallop population. Understanding the reaction of sea stars to this increase of sea scallops by investigating both large and small scale dynamics of the populations could provide insight into their predator-prey interactions. I hypothesized sea stars and sea scallops were aggregated, that sea scallop-sea star distributions (distances) are related to the density of scallops, and that sea stars are closer to smaller scallops. We used drop camera survey data from 2010 to 2018 to investigate these relationships in distribution. Annotated quadrat images were analyzed using the Spatstat package in R to create point patterns of locations of scallops and sea stars within the picture. Spatial point pattern analyses examined sea star-sea scallop distributions as well as nearest neighbor interactions and changes under varying densities of scallops. Morisita’s indexes and Ripley’s K-function indicate aggregation at the quadrat and station level on the scale of meters and ten of meters and clustering between sea stars, scallops, and sea stars with scallops within the quadrat on the scale of centimeters. Nearest neighbor frequencies suggest sea stars are found near smaller scallops (≤75 mm) scallops and larger scallops (>75 mm) scallops similarly. At higher densities scallops and sea stars were found clustered within 130 cm or less of each other. This increase in proximity could lead to more encounters and possibly captures of sea scallops by sea stars in densely populated beds created after extremely large recruitment events. Defining these small-scale predator prey distributions and interactions can help us understand natural mortality events and recruitment success of sea scallops associated with sea stars.