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Accommodation of the sex-ratio in eastern oysters Crassostrea virginica to variation in growth and mortality across the estuarine salinity gradient

Published online by Cambridge University Press:  24 April 2012

Eric N. Powell ,
Jason M. Morson ,
Kathryn A. Ashton-Alcox  and
Yungkul Kim
Eric N. Powell*
Affiliation:
Haskin Shellfish Research Laboratory, Rutgers University, 6959 Miller Avenue, Port Norris, NJ 08349
Jason M. Morson
Affiliation:
Haskin Shellfish Research Laboratory, Rutgers University, 6959 Miller Avenue, Port Norris, NJ 08349
Kathryn A. Ashton-Alcox
Affiliation:
Haskin Shellfish Research Laboratory, Rutgers University, 6959 Miller Avenue, Port Norris, NJ 08349
Yungkul Kim
Affiliation:
Department of Biology, Jackson State University, 1400 Lynch Street, Jackson, MS 39217
*
Correspondence should be addressed to: E.N. Powell, Haskin Shellfish Research Laboratory, Rutgers University, 6959 Miller Avenue, Port Norris, NJ 08349 email: [email protected]
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Abstract

Protandric oysters generate a relatively uniform reproductive potential over a wide range of environmental conditions that impose variations in growth rate and life span. Sex-at-length keys applied to survey data show that the female fraction routinely fell between 0.4 and 0.5, regardless of location in the salinity gradient. About 70% of population biomass is female over the same salinity range. Due to the necessary local modulation of the rate of male-to-female conversion to limit the influence of varying growth and life span over the salinity gradient, the number of males always exceeds by a small amount the number of females; thus improving the likelihood of a female having neighbouring males, a necessity for an immobile broadcast spawner. However, oysters at the extremes of the estuarine gradient all yielded populations with divergent sex-ratios. One consequence of reduced generation time brought about by increased mortality from disease should be selection favouring the switch from male to female at smaller size, if disease mortality is strongly female-biased. The site with the longest record of high mortality manifests such an increase. Sites up coastal rivers, putative refuges from disease, harbour animals with the slowest male-to-female conversion rates. Arguably these animals are most similar to the ancestral oyster pre-disease. Marketed animals range from 62% to 69% female. The principal influence of the fishery, and of oyster disease, would seem to be a reduction in lifetime egg production. Dermo disease may have reduced lifetime fecundity of females by nearly a factor of four.

Keywords

sex-ratiooystersalinity gradientsize-dependentage-dependentlifetime fecundityprotandryfishery bias
Type
Research Article
Information
Journal of the Marine Biological Association of the United Kingdom , Volume 93 , Special Issue 2: Fish and Fisheries , March 2013 , pp. 533 - 555
Copyright
Copyright © Marine Biological Association of the United Kingdom 2012

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