The impact of the non-native green crab (Carcinus maenus) on the susceptibility of eelgrass to wasting disease

Principal Investigator: Ruth Cox

In the northern Atlantic, eelgrasses provide an essential habitat for many ecological and commercially important fisheries, such as halibut, softshelled clams, Rock crab, salmon, oysters, and mussels. In many areas of the eastern Atlantic, including Prince Edward Island, the non-native green crab, is a significant pest that impacts eelgrass habitat by digging and degrading the quality of the eelgrass beds. It is also possible that damage caused by green crab to the eelgrass may make it more susceptible to wasting disease. Wasting disease tends to be more severe in degraded habitats; however, at present there is no direct evidence that demonstrates that green crab activity results in increased occurrence or severity of the disease.

We tested the hypotheses that 1) the presence of green crabs results in damage to eelgrass and thus reduces the density of eelgrass; and 2) the presence of green crabs results in greater prevalence and intensity of eelgrass wasting disease.

We found that green crab activity did not appear to have any effect on eelgrass vulnerability to wasting disease. There was a clear increase in the severity of disease through the course of the study, most likely related to the natural progression of the disease once some leaves are infected. The severity of eelgrass disease at the end of the experiment was as high as 30%, which indicates that the eelgrass beds may have been under stress from one or more factors not examined in this study.