Morphological Evidence of Phenotypic Plasticity in Shells of Oyster ( Crassostrea tulipa ) From Sub‐Habitats in the Densu Estuary, Ghana

ABSTRACT The West African mangrove oyster, Crassostrea tulipa , exhibits high variability in shell morphology, which is influenced by both genetic and environmental factors. The current study investigated the plasticity of C. tulipa sub‐populations within the Densu Estuary, Ghana, from May 2017 to October 2018 with respect to shell morphology, as impacted by some environmental parameters. The study is aimed at providing useful information on the plasticity of oysters in the face of harsh environmental conditions with respect to shell development. The study was carried out in Stations 1, 2, 3 and 4 (a and b), where oysters were present in Stations 3, 4a and 4b. Allometric studies were carried out on oyster samples from three sub‐populations within the Densu Estuary. Temperature, DO, salinity, pH and turbidity were monitored. Bulk density of sediments at the sub‐populations was determined. There was no marked difference in the variations of the physico‐chemical parameters between Station 3 and Station 4 oysters, except for sediment bulk density. There was evidence of high mortality and low population density of oysters at Station 3, as compared to its counterparts. The slopes of the regression of shell height against shell length/total shell weight/wet meat weight of oysters from the various sampling stations showed negative allometry. Oysters at Station 3 showed isometric growth from the regression of shell width on shell height. Station 3 oysters demonstrated higher condition indices and gonadal indices indicative of better physiological status. The findings indicated that Station 3 oysters exhibited morphometric traits consistent with enhanced reproductive potential by demonstrating phenotypic plasticity through the development of bigger inner shell volume for gonadal development and maturation at small shell size in the face of harsh environmental conditions.