Meeting Abstract

70.5  Monday, Jan. 6 09:00  Size-at-age vs. size-at-stage: Environmental control of blue crab growth rates DARNELL, M.Z.; Nicholls State University, Thibodaux, LA zachary.darnell@nicholls.edu

Blue crab (Callinectes sapidus) size-at-maturity has decreased throughout much of their range where there are commercial fisheries. It has been hypothesized that this may be due to either genetic or environmental factors. Field surveys throughout the range have found both temporal and spatial trends in size-at-maturity, supporting the hypothesis that size and growth rates are strongly influenced by the environment. In particular, crabs reach maturity at larger sizes in low salinity, cool areas, while they reach maturity at smaller sizes in high salinity, warm areas. Like all crustaceans, blue crabs grow discontinuously, increasing in size only during the molt. Growth rate is thus defined by two factors: intermolt period (IMP), the length of time between molts, and the growth per molt (GPM). We investigated the effects of salinity and temperature on blue crab IMP and GPM in a laboratory experiment. Crabs were collected as megalopae and held in one of six treatments until the 6th juvenile stage. All crabs were fed daily and measured following each molt. While salinity did not have a significant effect on any aspect of growth, temperature significantly affected both IMP and GPM. Higher temperature reduced both IMP and GPM. Thus, crabs reared at 30°C molted more frequently than crabs reared at 20°C, but exhibited less growth at each molt, resulting in a smaller size at each stage. These results suggest that temperature plays an important role in determining blue crab growth rates and size-at-maturity. Although salinity did not affect growth in this experiment, relationships between salinity and size observed in the field may be due to indirect effects of salinity on growth mediated through effects on food quality or food availability.