Honors College

Document Type

Honors Thesis


Marine Science


Ian Bricknell

Committee Members

Timothy Bowden, Kristina Cammen, Mark Haggerty, Heather Hamlin

Graduation Year

May 2020

Publication Date

Spring 5-2020


Carcinus maenas (European green crab) is an invasive species that made its way to North American waters in the 1800s on European trading ships. As an invasive species they cause problems by competing with native species for the resources within their shared ecosystem. They can also introduce pathogens that can infect and wreak havoc on native populations. In Nova Scotia, Bojko et al. (2017) found the pathogen Parahepatospora carcini, a clade IV microsporidian parasite found in the hepatopancreas of aquatic arthropods, in C. maenas. Because this case was located within close range of Maine waters, the objective of this study was to determine if Maine’s green crab population was also infected. In a sample of 500 green crabs, seven were found to be infected, resulting in a 1.4% prevalence of P. carcini within the C. maenas population of Maine. The seven infected crabs had a smaller range and average size than the entire sample, suggesting that C. maenas might not survive long after infection or that growth is stunted due to lack of energy stores. P. carcini prevalence in this sample peaked just before mid-July, then tapered off later in the month indicating that there could be a seasonal component to the parasite's life cycle. However, a larger sample size and a year round collection would be needed to determine if these factors have a significant correlation with P. carcini prevalence. Sample location, crab sex, and organ color had no correlation with infection prevalence. PCR resulted in a pathogen band at 939 bp in all seven samples, which was determined to be from a microsporidian DNA by sequencing an excised and purified band. Histology was used to confirm P. carcini infection in all seven samples with both H&E and trichrome staining techniques.