Date of Award



© 2015 Anthony Himes

Document Type


Degree Name

Master of Science in Marine Sciences


Marine Science

First Advisor

Markus Frederich

Second Advisor

Anna Bass

Third Advisor

Donald Mykles


The European green crab, Carcinus maenas, is a highly invasive species found throughout the world with severe economic and ecological impacts on the regions it invades. This species occurs in two color morphs: green after molting and red after prolonged intermolt. Physiological variations between these two morphs are well documented across various environmental conditions, but little work has focused on female C. maenas. To assess if the variation between color morphs observed in males persists in females, red and green morphs of each sex were exposed to a constant low salinity environment. Constant low salinity exposure was chosen as it has been widely used throughout the literature, but it is not representative of the tidal environment this species inhabits. Therefore, we exposed morphs from each sex to an oscillating salinity environment to better replicate natural conditions. We employed several whole animal and molecular techniques to evaluate differences in physiological tolerance between each color morph and sex when subjected to both low and oscillating salinity environments.

Our results for low salinity exposure were consistent with previous findings that green morphs outperform red morphs in whole animal assessments and demonstrated increased upregulation of the key enzymes involved in ion regulation, Na+K+-ATPase and two forms of carbonic anhydrase. However, we found that both red and green female morphs outperformed their male counterparts in our whole animal assessments and demonstrated higher overall gene expression levels than males. These patterns were also observed under oscillating salinity conditions, but oscillating salinity was found to be less strenuous than low salinity resulting in better whole animal performance and less gene upregulation. We hoped our RNA sequencing pilot study would allow us to more completely evaluate the osmoregulatory mechanism as well as any other secondary mechanisms involved in response to these exposures, but our small-scale approach did not yield enough sequencing coverage to accomplish this. The lower expression levels observed for the osmoregulatory mechanism in the oscillating salinity exposure make it difficult to accept that the new synthesis of these various proteins are directly involved in the daily low salinity encounters for this species. Alternatively, our findings reveal the possibility of a large cellular pool of these proteins that is available for short-term low salinity exposures, or that an alternative osmoregulatory mechanism is employed. These differential tolerances between color morphs could be key to management strategies as our population survey data has revealed that the weaker red morphs are more abundant in late spring and early summer where the population as a whole is more vulnerable to environmental challenges. Overall, these data demonstrate that not only do the different color morphs and sexes need to be accounted for in future physiological studies, but that more representative environmental conditions need to be employed as well.


Master's thesis

The first chapter of this thesis contributed to the following publication:
Pennoyer KE, Himes AR, Frederich M (2016) Effects of sex and color phase on ion regulation in the invasive European green crab, Carcinus maenas. Marine Biology 163 (6): 137. doi:10.1007/s00227-016-2910-2

The second chapter of this thesis contributed to the following publication:
Himes AR, Balschi WS, Pelletier G, Frederich M (2017) Color Phase-Specific Ion Regulation of the European Green Crab Carcinus maenas in an Oscillating Salinity Environment. Journal of Shellfish Research 36 (2): 465-479. doi: 10.2983/035.036.0218