Reproductive and Recruitment Dynamics of Clionaid Sponges on Oyster Reefs in North Carolina

Boring sponges belonging to the family Clionaidae have become a destructive nuisance to eastern oyster (Crassostrea virginica) aquaculture and restoration efforts in the southeastern USA. Clionaid sponges colonize the inner layers of oyster shells and remove carbonate material, compromising the quality and marketability of the oyster; however, relatively little is known about reproduction and recruitment of these sponges. Using histological techniques, reproductive activity of clionaid sponges was monitored at two sites (Cedar Island and Masonboro Sound) in coastal North Carolina. Sponge recruitment to limestone tiles (5×5 cm), oyster shells, and clam shells was monitored in 2013 and 2014; recruitment to the limestone tiles was statistically higher than recruitment to clam or oyster shells. Overall, seasonal patterns in reproduction and recruitment of clionaid sponges were generally similar at the two sites. Three species of clionaid sponge were found during field sampling (Cliona celata, C. lobata, and C. truitti), and reproductive activity (eggs and spermatocysts) of these species was observed from April to November, with peak reproduction occurring from June to September for C. lobata and from August to September for C. celata. Recruitment peaked in late summer/early fall. Additionally, the relationship between environmental conditions (temperature, salinity, dissolved oxygen, pH, and chlorophyll a) and clionaid recruitment was explored using a regression model. At Cedar Island, the best‐fit model included salinity and dissolved oxygen, while the best‐fit model at Masonboro Sound included temperature, pH, and salinity. The data from this study show that the primary reproduction and recruitment pulses occur in the fall for local clionaids, and thus mitigation strategies should be applied in the late fall or winter to minimize infestations