Examining the Threat of an Invasive Species on Shellfish Aquaculture

Project Description

Green crabs are the model species for an invasive organism. They have major economic and environmental impacts on Maine’s ecosystems by predating many aquacultured organisms (such as soft shelled clams) and destroying salt marshes and infrastructure by burrowing under moorings, quays, etc. Green crabs have been established in the state since the 1800’s and are successful due to their escape from natural predators and parasites inhabiting their native range. However, recent research shows that the impact of parasites on green crabs is underestimated.

In Maine, green crabs only have two known parasites; the spiny-headed Acanthocephalan worm Profilicollis botulus and Microphallus Spp, a parasite identified by Theme 2 in May 2016. By investigating the ecological dynamics of P. botulus and green crabs in the three bioregions, as well as the parasite prevalence in the eider duck definitive host, it is possible to investigate the parasite-host relationships with regard to organismal fitness and climate change. This will provide data that can be used to verify models being developed by Theme 1 that observe invasive species distribution in Maine and the likelihood of expansion over the next century.

Results and Accomplishments

In 2017-2018, project personnel discovered that the prevalence of P. botulus in green crabs was higher in bioregion 1 (Southern Maine) than bioregions 2 or 3 (Midcoast and Downeast Maine). However, the results did not achieve the same sample size as that achieved in Year 3, when over 3,000 green crabs were sampled. This investigation will be continued in Summer 2018.

A group of citizen scientists was established using the iNaturalist web resource to continue work on the definitive host of P. botulus. A small, but growing, group of duck hunters was recruited to record the presence of P botulus photographically. This allows an estimation of the parasite prevalence and intensity in the definitive host to be established in a population far larger than can be directly sampled.

The assessment of parasite intensity of P. botulus in eider ducks continues. The Maine duck populations seem to have a high prevalence and high intensity of parasites; especially when compared to published data. The significance of this result requires further research. It could suggest the eider duck population is under stress, or that green crabs have replaced the traditional prey items of eiders, such as blue mussels or stone cabs, thereby increasing the burden of P botulus in its host.

Results and Accomplishments

Data Type Quantity Location
Crab parasitology Spreadsheets and laboratory notebooks 4,500 data points to date Samples collected coast wide, Bricknell Laboratory, UMaine
Molecular data Biochemical circa 300 Bricknell Laboratory, UMaine
DNA for sequencing (parasite cDNA) Biochemical circa 300 Bricknell Laboratory, UMaine