Voracity of invasive European green crabs versus native red rock crabs explored in BMSC Alumni publication

Although the invasive European green crab (Carcinus maenas) has cost commercial aquaculture millions of dollars on the East coast of North America, studies on the potential impacts of this notorious invader on shellfish on the West coast are lacking. Fall Program 2018 students Em Lim and Nic Ens set out to address this knowledge gap by comparing the predatory impacts of the invasive green crab with the native red rock crab (Cancer productus). Inspired by Brett Howard’s work and under Tao Eastham’s supervision, the students decided to assess feeding behaviours using functional response analysis, which provides information about how predators find and consume prey as a function of prey abundance. Em and Nic watched how each crab species fed upon pacific oysters in individual tanks at BMSC to perform these analyses and determine how the European green crab might square up next to the red rock crab as oyster predators.

This research revealed a surprising difference in predatory behaviour between the two crab species! Invasive green crabs ate as many oysters as possible regardless of how many oysters they were presented with, following a Type II (asymptotic) functional response. However, the native red rock crab didn’t consume oysters until prey were adequately abundant, following a Type III (sigmoidal) functional response. Therefore, oysters may experience a low-density refuge from red rock crabs, which would allow populations to recover when they are diminished. However, invasive green crabs will continue to decimate prey, even at low densities. European green crabs consume nearly as many oysters per crab per hour as red rock crabs but can build to greater population densities. This may mean that the green crabs may become the greater threat to oyster aquaculture in BC as populations expand.

Ens, N.J., Lim, E.G., Howard, B.R. et al. A comparison of the predatory impacts of an invasive and native crab species using a functional response approach. Biol Invasions (2021). https://doi.org/10.1007/s10530-021-02508-5