Temporal Variation In Fecundity And Spawning In The Eastern Oyster, Crassostrea Virginica, In The Piankatank River, Virginia

Oysters of the genus Crassostrea are considered good examples of an r-selected marine invertebrate with small egg size, high fecundity, and multiple spawning events per year, each characterized by significant individual weight loss. Historical (decadal) data for the Virginia portion of the Chesapeake Bay support these generalities. We present recent (subdecadal) data, collected for natural Crassostrea virginica broodstock of populations in the Piankatank River, Virginia. The relationship is described between oyster size, fecundity, spawning periodicity, and egg viability for natural broodstock. Oysters collected throughout the summers of 2010 through 2012 and induced to spawn by thermal cycling released viable eggs on 7 dates (n = 119 oysters, 35male, 84 female; shell length (SL) range, 58-113 mm). Oysters were opened to examine sex ratio on four additional dates (total n = 242 oysters, 82 male, 160 female). Fecundity varied in the range 10(5)-1.2x10(8) eggs. When all data are considered in unison, no strong relationship with SL is evident; however, when eliminating the artifact of data corresponding to minimal egg release, a much stronger relationship, comparable with that reported in older literature, emerges. Female fraction (Female/(Female + Male)) was consistently more than 1 in oysters larger than 60 mm in SL (estimated age, \u3e= 2 y), generally in accordance with recently published literature on the species in themid-Atlantic. The size-versus-fecundity relationship does not appear to be greatly influenced by disease prevalence/intensity. The temporal sequence of spawning activity was not observed to continue after midsummer and is not commensurate with a cumulative degree-day estimator during the latter half of the well-documented historical spawning season. A size-fecundity estimator for the Piankatank River oysters provides a basis to estimate the disproportionate value of larger/older (\u3e= 3 y) oysters in the system, and provides additional input to the fine-tuning of a previously developed rotational harvest schedule for the river stock. The possible impact of recent changes in water quality, seasonal occurrence of dinoflagellate blooms, and/or long-term impacts of changing regimes were not examined in detail in this study but are suggested as worthy lines of future investigation