Date of Award

Summer 8-2019

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

Richard Wahle

Second Committee Member

David Fields

Third Committee Member

Paul Rawson

Additional Committee Members

Spencer Greenwood

Abstract

Anthropogenic carbon released into the atmosphere is driving rapid, concurrent increases in temperature and acidity across the world’s oceans, most prominently in northern latitudes. The geographic range of the iconic American lobster (Homarus americanus) spans a steep thermal gradient and one of the most rapidly warming oceanic environments. Understanding the interactive effects of ocean warming and acidification on this species’ most vulnerable early life stages is important to predict its response to climate change on a stage-specific and population level. This study compares the responses of lobster larvae from two sub-populations spanning New England’s north-south temperature gradient (southern New England and eastern Gulf of Maine) to the joint effects of elevated pCO2 and temperature. Using a full factorial experimental design, we subjected planktonic larval and post-larval stages to different combinations of ambient, end-century projected, and extreme pCO2 concentrations (400 ppm, 750 ppm, 1200 ppm), and ambient and projected end-century temperatures (16°C and 19°C). We measured larval growth (both linear and dry weight), oxygen consumption, and elemental composition. In addition, with postlarvae, we quantified swimming speed and feeding behavior. Our experiments suggested that elevated temperature has a larger influence over measured parameters than elevated pCO2 alone, resulting in faster development times of all larvae. However, responses in other measured parameters were location and stage-specific, suggesting that larvae from contrasting thermal regimes respond differently to elevated pCO2 and temperature. Larvae from southern New England were more responsive to temperature than pCO2 stress, resulting in a longer carapace and greater dry, carbon and nitrogen weights in stage II when reared at elevated temperature. Larvae from eastern Gulf of Maine, however, more often showed no treatment effects, grew to longer carapace lengths, had greater elemental and dry weights and exhibited higher rates of oxygen consumption than southern New England larvae, despite starting at the same elemental weight and carapace length at stage I.

In addition, this study also investigated the interactive effects of ocean warming and acidification on the gene expression response of the planktonic postlarval lobster from southern New England. Using a full factorial experimental design, lobsters were raised in ambient and elevated pCO2 concentrations (400ppm, 1200 ppm) and temperatures (16°C and 19°C). When temperature alone was elevated (19°C), larvae downregulated genes related to cuticle development; when pCO2 alone was elevated (1200 ppm), larvae upregulated chitinase as well as genes related to stress response and immune function. The joint effects of end-century stressors (19°C, 1200ppm) resulted in the upregulation of those same genes, as well as cellulase, and the downregulation of calcified cuticle proteins, and a greater upregulation in genes tied to immune response and functioning. These first results of the impact of varying conditions on larval lobster gene expression suggest the existence of compensatory mechanisms in response to stressors resulting from a rapidly changing environment.

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