TIDAL HEIGHT AND GAMETOGENESIS: REPRODUCTIVE VARIATION AMONG POPULATIONS OF GEUKENSIA DEMISSA

¹ Department of Biology and Belle W. Baruch Institute, University of South Carolina, Columbia, South Carolina 29208

High tidal populations of the mussel Geukensia demissa experience reduced filter feeding time as a result of aerial exposure. This study tested the hypothesis that such populations exhibit a temporal delay in their gametogenic cycle compared to populations from the low intertidal. As predicted, quantitative estimations of gametogenic condition of mussels from 10 high tidal populations were lower than those of mussels from 11 low intertidal populations in May 1986. A two-fold difference in potential feeding time was accompanied by a delay of about two months in the reproductive activity of high tidal mussels. This study demonstrates that temporal reproductive variation among populations of G. demissa across the intertidal zone may be as large, or larger than variation among latitudinally separated populations of this species. Site-to-site variation in timing of reproduction within the North Inlet Estuary may also be as large as temporal latitudinal variation. Level of occurrence in the intertidal zone and hence length of submersion and potential feeding time exert profound influence in the timing of the reproductive cycle of the ribbed mussel, Geukensia demissa.