Date of Award

Spring 5-30-2018

Level of Access

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Bio-Resources

Advisor

Robert Bayer

Second Committee Member

Sarah Barker

Third Committee Member

Cem Giray

Additional Committee Members

Heather Hamlin

Carol Kim

Abstract

The American lobster, Homarus americanus, H. Milne Edwards, 1837, supports the most economically valuable fishery along the North Atlantic coast of North America. A collapse in lobster populations in Southern New England (SNE) has coincided with increasing ocean temperatures and emerging diseases. This research investigated the etiologies of limp lobster disease (LLD) and epizootic shell disease (ESD), two diseases that continue to cause significant mortality in natural lobster populations. Mortality from LLD is associated with the bacteria Photobacterium indicum and is more intense in impounded lobsters. To more clearly define the community ecology of this suspected opportunistic pathogen, the microbial biofilms of freshly captured and impounded adult lobsters from the Northern Gulf of Maine coastal shelf were surveyed and compared. P. indicum was found to be a common member of the microbial communities of freshly captured and impounded H. americanus and was also isolated from the lobster pound sediment. There is no medicated feed that is approved for use in controlling P. indicum. Therefore, a P. indicum bacterin was produced and used as an immunostimulant to stimulate a short-term protective immune response in adult American lobsters. The prepared bacterin was safe to use with lobsters and no adverse reactions were observed. Epizootic shell disease (ESD) is an aggressive form of shell disease likely involving multiple microbes. A laboratory study was performed to examine the effects of three seasonal temperature cycles on the immune response and progression of ESD in adult female American lobsters. There was a trend of increased mortality in the diseased lobsters in the mid- and high-temperature seasonal cycles. Both temperature and shell disease influence bacterial loads. The culture dependent microbial diversity remained relatively stable over time and temperature suggesting that increasing temperatures alone did not exacerbate ESD progression or alter microbial communities. Taken together, this work increases our understanding of the etiology of the factors that could influence population abundance and disease emergence in lobsters.

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