Brood-dependent morphology, behavior, and biophysical interactions among blue crab (Callinectes sapidus) zoeae
Creators: name: Caracappa, Joseph Charles
Publisher: name: No Publisher Supplied
Year: 2019

description: The goal of this dissertation is to provide a better understanding of the intraspecific variability in morphology and swimming behavior, as well as some of the implications of such variation, in early stage Callinectes sapidus zoeae. A long-standing body of work has demonstrated that zoeal morphology is not constant, and morphological features can have an important role in survival and behavior. Additionally, given the presence in brood-dependent morphology in other species and the susceptibility of blue crab life history to generate maternal effects, the presence and magnitude of differences among larval broods should be addressed. In the second chapter, variation in C. sapidus zoeal morphology among several larval broods was identified, and used to test whether brood-dependent morphology is present. This experiment involved hatching several broods, making measurements using microscope photography, and image analysis. Simple models of swimming-induced drag and passive sinking velocity were used to create an index of vertical swimming efficiency. Results discussed in Chapter 2 demonstrate that morphology can vary significantly between broods, and these differences can translate to differing swimming efficiency. In the third chapter, larvae from the same broods described in Chapter 2 were followed further into development to investigate how brood-level morphological differences change over development. By the time of their second molt, broods of zoeae retain most differences in morphological size and shape, but shape difference decrease. These results suggest that over time, brood effects can persist, but there is a detectible morphological convergence, and differences in swimming efficiency are still present. Chapter four tested whether the brood-dependent morphology discussed in the prior chapters translated to similar differences in swimming behavior. Using mesocosm video observations, significant differences in the swimming velocity, orientation, and path straightness of larval broods was confirmed. Despite these differences, distinct modes of behavior that were conserved across broods were observed. These represent differences in swimming behavior within broods either between individuals or over time. In the fifth chapter, simulations were used to test whether the observed brood-dependent behavior and morphology can translate to differences in larval transport. A simplified model of a wind-driven estuarine plume with a sheared current was used, along with observed brood-depending swimming and sinking behaviors, to model larval transport. Model results showed brood-dependent and behaviorally-driven larval transport, where faster-swimming broods of larvae are more able to counter wind-driven vertical mixing and stay in surface waters. Likewise, the type of depth-regulation zoeae use can influence how they are transported. Overall, this dissertation finds that morphological and behavioral traits can differ substantially between larval broods. These results suggest that there may be differential success of larvae from different broods. I recommend that future work could focus on identifying maternal or environmental predictors of larval condition. Additionally, future models of C. sapidus larval dispersal should incorporate observed behavior and its variability.