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

Primary Investigator: Ruth Cox

In the northern Atlantic, eelgrasses provide an essential habitat for many ecological and commercially important fisheries, e.g. 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 (Carcinus maenus), is a significant pest; as an ecosystem engineer it impacts eelgrass habitat via 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 infection by the pathogen Labyrinthula zosterae, which results in wasting disease. Wasting disease tends to be more severe in degraded habitats; however, at present there is no direct evidence that demonstrates that the actions of the green crab result in increased occurrence or severity of the disease.

Work currently underway (at UPEI) aims to assess the resilience of coastal ecosystems in PEI to green crab introduction and removal. The work proposed here complements the existing project, and will quantify the impact of green crab at different densities on the susceptibility of eelgrass to wasting disease via experimental manipulation of green crab populations in the field.

We will test the hypotheses that:

  1. Presence of green crab (adults or juveniles) results in damage to eelgrass and, thus, reduces the density of eelgrass. Green crabs also alter the demography (size of plants and amount of flowering) of eelgrass.
  2. Presence of green crab (adults or juveniles) results in greater prevalence and intensity of eelgrass wasting disease.