Date of Award

Winter 12-27-2018

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)


Marine Biology


Mark Wells

Second Committee Member

Lee Karp-Boss

Third Committee Member

David Townsend

Additional Committee Members

Lawrence Mayer


The increases in ocean temperature and pCO2 due to climate change are projected to affect the growth and future prevalence of Harmful Algal Blooms (HABs) in nearshore waters, but systematic studies on the effects these climate drivers have on harmful algal species are lacking. In particular, little is known about how future climate scenarios will affect the growth of the toxic dinoflagellate Alexandrium catenella, which produces the toxins responsible for paralytic shellfish poisoning (PSP) that threaten the health and economy of coastal communities in the Gulf of Maine. I examined growth responses of A. catenella and two other naturally co-occurring dinoflagellates from Gulf of Maine— Scrippsiella sp., and Amphidinium carterae— in mono and mixed species cultures. Experimental treatments included elevated temperature, lower pH, and the combination of elevated temperature and lower pH as projected for the year 2100 (20°C; pH 7.8), relative to current conditions (15.5°C; pH 8.1). Results show decreased growth rates of A. catenella under elevated temperature and lower pH, and that the decreased in growth rate was largely attributable to the effect of temperature. In contrast, the growth rates of Scrippsiella sp. and A. carterae increased under elevated temperature and lower pH conditions, with temperature being the primary driver of the response. These trends did not change substantially when these species were grown in mixed cultures (A. catenella + Scrippsiella sp., and A. catenella + A. carterae), indicating that allelopathic or competitive interactions did not affect the experimental outcome under the conditions tested. These findings suggest that A. catenella blooms will become less prevalent in the Gulf of Maine with continued climate change, shifting instead to a dominance by other dinoflagellate species.