Effect of sediment grain size and oyster presence on oyster drill abundance

Oysters are the focus of many conservation and restoration projects; however, little is known about habitat preferences for their primary predator, oyster drills. Oyster drills ( Stramonita haemastoma complex) are recognized as significant oyster predators, posing a threat to oyster populations and the success of conservation and restoration efforts using oysters. Oyster drill abundance is known to be influenced by salinity, with a preference for higher salinities; however, drill abundances vary widely within homogeneous salinity zones. We assessed the impact of substrate type and oyster presence on oyster drill abundances along the coastal regions of Mississippi and Alabama. Eight sites were used that included a combination of locations with oysters present or absent and either fine or coarse sediment. Oyster drill abundances were quantified using baited traps deployed parallel to the shoreline every 4 wk between May and October 2023. Statistical analyses revealed that sampling event (seasonality) had a strong effect on drill abundance, with abundances increasing over time. Sampling event also interacted significantly with both sediment and oyster presence, influencing abundance patterns. Significant differences were observed in oyster drill abundances between sampling events grouped by oyster presence, with farms exhibiting higher abundances. However, sediment type only significantly influenced drill abundances during the first 2 sampling events. Results of this study suggest that factors other than salinity and oyster presence, such as sediment type, may influence oyster drill abundances differently throughout the year. Results from this study can be used to develop future studies and inform oyster management.