Characterizing The Effects Of Environmental Stressors On The Physiology And Behavior Of Commercially Important Marine Invertebrates

I examined the effects of acidification – both alone and in combination with other environmental changes – on two commercially, ecologically, and culturally important marine invertebrates, the American lobster Homarus americanus and the Eastern oyster Crassostrea virginica. Both H. americanus and C. virginica reside in coastal ecosystems where ocean and coastal acidification are expected to affect the normal variability of carbonate chemistry. The effects of acidification are expected to act in concert with other changing environmental parameters to alter the condition of individual organisms, with eventual impacts on marine populations and communities. My objective was to understand how the American lobster and Eastern oyster respond to acidification from a holistic perspective by examining a variety of response metrics, life stages, stressor combinations, exposure durations, and exposure intensities. With this goal in mind, in Chapter II I describe the physiological responses of American lobster embryos to acute exposure to conditions of acidification. Short-term exposure to acidification conditions were associated with hypercapnia-induced oxidative stress and disrupted acid-base status in lobster embryos. In Chapter III, I explore whether this sensitivity to acidification is shaped by environmental history. Specifically, I examined physiological responses of American lobster embryos to acute acidification exposure were examined following long-term rearing under one of two thermal conditions. I also measured the responses of stage I larvae to acute acidification exposure were measured following brooding under one of two thermal and two carbonate chemistry treatments. Environmental history, and particularly thermal history, shaped both embryo and larval sensitivity to acute acidification exposure. In Chapter IV, I describe parental behavior as an additional mechanism by which the sensitivity of American lobster embryos to acidification exposure may be modulated. Specifically, I examined brood-grooming behavior in ovigerous H. americanus females was examined over embryogenesis during exposure to one of two thermal and carbonate chemistry treatments. While brood-grooming behavior was sensitive to embryo developmental stage, it did not differ significantly among treatment groups, suggesting that the effects of chronic exposure to warming and acidification may not be moderated by parental behavior. In Chapters II-IV, I identify a number of metrics that are sensitive to acidification in the American lobster, including enzyme activity rates and damage from oxidative stress. In Chapter IV, I evaluated existing indicators of condition of the Eastern oyster in a variety of laboratory and field conditions to identify their future utility as ocean acidification progresses. Although metrics of oyster size and health were generally well correlated, indices of condition differed in their sensitivity to carbonate chemistry. These observations do not support the utility of a single condition index for monitoring individuals from different carbonate chemistry environments. For the American lobster and Eastern oyster, understanding the potential effects of future climate change conditions is important for maintaining their commercial sustainability and ecological value. In aggregate, my work reflects the range of environmental conditions that coastal invertebrates will experience in future decades, including a range of exposure intensity and duration, supporting the need for experimental designs that utilize location specific data and projections for treatments. My dissertation highlights the importance of integrating multiple indicators of organismal performance to capture responses to acidification by demonstrating that physiology, behavior, and condition can all respond differently to environmental stressors.