Spatial Modeling of Oyster Drill Habitat Preferences in Richardson Bay, California

Abstract

The Atlantic oyster drill Urosalpinx cinerea is an introduced muricid whelk in San Francisco Bay that has posed significant challenges to Olympia oyster restoration projects on the United States West Coast. Atlantic oyster drills have a patchy spatial pattern of presence and absence in San Francisco Bay and occur in a range of abundances where they are present. This project incorporated substrate composition, elevation, water temperature, salinity, inundation, and drill abundance data that I collected from summer 2017 to summer 2018 at eight sites in Richardson Bay, an embayment of San Francisco Bay, to model the significance of key abiotic habitat factors. Using generalized linear mixed effects models with logistic and negative binomial distributions, I determined that amount of coarse substrate cover and elevation above mean lower low water are significant environmental factors associated with drill abundance. Consequently, the absence of Atlantic drills from parts of Richardson Bay is not due to a lack of coarse substrate cover at significant elevations. My hope is that these model results will contribute to appropriate site selection of Olympia oyster restoration projects.