Tidal level affects the prevalence and impacts of pests and parasites on oysters (Crassostrea virginica) on intertidal reefs in Georgia, USA

Abstract

Oysters (Crassostrea virginica) provide multiple ecosystem services to coastal habitats. Due to their declines, numerous restoration efforts target oysters, making it critical to explore factors that might limit recovery. Biotic stressors, such as pea crabs and boring sponges, can negatively affect oysters, and may interact with abiotic stressors like tidal exposure. In this study, boring sponge and pea crab distribution patterns were explored across an intertidal gradient on oyster reefs in Georgia (32.002° N, − 080.920° W) in the summer of 2016, while considering the effects of both stressors on oyster condition. Boring sponges and pea crabs were both most abundant on the lower intertidal of reefs (15% and 6% prevalence, respectively) and decreased with increasing tidal exposure (~ 1% prevalence of both pests in the upper intertidal). Pea crabs had a more negative effect on oyster condition in the upper intertidal zone (27% difference), whereas boring sponges caused the greatest condition reduction in the lower intertidal zone (30% difference). Pea crabs were more abundant in sponge-infected oysters than uninfected oysters. An observed negative relationship between oyster density and sponges suggests that higher sponge prevalence may drive low oyster density in the lower intertidal zone. Since biotic stressors on oyster reefs can affect oyster population structure and reef function, understanding their distribution and interactions is important for management and restoration. While sponges and pea crabs are not likely to be eliminated by restoration efforts, careful attention to location within the tidal prism can minimize their impacts on restoration efforts, particularly in the southeastern USA.