Variability in swimming behavior among broods of blue crab (Callinectes sapidus) zoeae

Abstract

Blue crabs (Callinectes sapidus) support economically important fisheries across the eastern United States, which have exhibited historical variability in recruitment. Blue crab zoeae develop in surface waters over the continental shelf, where they need to constantly swim upward in order to stay within surface currents to successfully disperse. Morphology influences the drag zoeae experience and their ability to produce thrust, and morphological traits can vary across the population, especially between larval broods. The objectives of this study were to characterize the swimming behavior of first stage C. sapidus zoeae, determine whether there were inter-brood differences in swimming behavior, and identify morphological traits that are correlated with swimming behavior. The swimming behavior of zoeae from nine blue crab broods were observed within 24 h of hatching using video recordings, and metrics relating to velocity, orientation, and path straightness were calculated. Individual zoeae exhibited substantial variability in behavior, and broods significantly differed for all behavioral metrics measured. A mixture model analysis identified two modes of behavior each for velocity, orientation, and path straightness. These behavioral modes exist within individual broods, but the proportions exhibiting each behavior varied. Some morphometrics were significantly correlated with behavior, though some hypotheses based on the theoretical mechanics of zoeal swimming were not confirmed. Zoeal swimming ability, in terms of velocity and path straightness, varies among individuals within broods, yet across broods patterns of behavior were somewhat similar. The behavioral groups observed may result in inequality in the energetic costs of swimming for zoeae within a given brood, as well as varying optimization of vertical swimming. These results highlight the importance of individual and brood variation in swimming behavior and demonstrate the relationship of morphology in determining swimming behavior. Future work investigating zoeal swimming mechanics and behavior should incorporate this population-level variation.