The northern coquina clam, Donax fossor, is often found in association with the hydroid Lovenella gracilis in the intertidal zone of exposed sandy beaches of southern New Jersey. Although previous workers have suggested that the Donax-Lovenella relationship is one of commensalism, this assumption rarely has been quantified or experimentally investigated. Our objectives are: (1) to eliminate the possibility that the association is a recent occurrence, (2) to quantify whether the hydroid has any affect on predation rates of the clam, (3) to quantify the effect of the hydroid on the ability of the clam to swash-ride, and (4) to document seasonal variation in the association. Monthly field samples collected at two sites over a 2-y period revealed that D. fossor and L. gracilis are seasonal in occurrence. The proportion of the D. fossor population with an epibiotic hydroid varied among season, clam size, and field site. Hydroid abundance also varied between years, among seasons, and between field sites. Overall, larger clams were more likely to support a hydroid colony than smaller clams. Predation by the moonsnail Neverita duplicata on D. fossor was affected by the presence of L. gracilis. Clams without a hydroid colony were drilled more frequently than clams with a hydroid colony, suggesting that D. fossor benefits from the hydroid by way of predator deterrence. The results of this study indicate that the Donax-Lovenella association is quite common during the summer months although it has been overlooked for decades. The evidence to date implies that the Donax-Lovenella relationship is a candidate for a case of mutualism because of the reduced predation rates by moonsnails on clams with a hydroid colony.
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Vol. 24 • No. 1