Movement and energetics of swimming marine mollusks

Abstract

Mollusks constitute a significant proportion of marine animal biomass and fulfill essential ecosystem functions. Yet, our knowledge of their behavior and energy output in natural environments remains elusive. This key knowledge gap stems from our inability to quantify their positions and movements for appreciable time-scales, and thus we know extremely little about how abundant mollusks that are pervasive in all ocean biomes respond to naturally varying and anthropogenically-induced changes. In this thesis, I adapted emerging biologging sensor technology, traditionally designed for large robust vertebrates, for two key mollusk taxonomic groups (squid and scallops) to quantify and characterize movements at fine-temporal scales. In Chapter 2, I collected the first high-resolution (> 1 Hz) in situ movement data for any squid species. These novel data elucidated fundamental swimming behaviors such as swim direction, postures, and environmental extents of ecologically-vital diel vertical migration. In Chapter 3, I linked lab-calibrated bioenergetic models and field observations to map energy output and necessary caloric intake of natural behaviors in the wild. These data revealed dynamic gait use on seconds time scales. Next, in Chapters 4 and 5, I quantified the behavioral disruption and the metabolic cost of a prominent anthropogenic stressor, sound pollution. Squid and scallops elicited drastically different ecophysiological responses to field-simulated offshore windfarm construction. Squid elicited dramatic behavioral responses coinciding with the onset of construction, although animals habituated rapidly. Contrarily, scallops’ behavioral responses were moderate but consistent, and surprisingly there was no evidence of habituation across second, minutes, and daily time scales. Extended behavioral changes manifested as heightened metabolic rates and weakened antipredator responses, suggesting prolonged and potential population-level impacts on a key fishery. This thesis provides new insight in marine invertebrate movement ecology and eco-physiology, demonstrating the utility of coupling biologging and physiological experiments to reveal how key ocean animals behave and expend energy.