Flexible prey handling, preference and a novel capture technique in invasive, sub-adult Chinese mitten crabs

Eriocheir sinensis (Crustacea: Brachyura: Varunidae) is one of only two crabs on the world’s list of 100 most invasive aquatic invertebrates. This crab has successfully invaded NE Europe as well as well as the United States, eastern Canada, southern Iraq and Tokyo Bay, Japan. In England, the River Thames population of E. sinensis continues to increase in numbers and disperse westward upstream, although little is known about foraging. The present study undertook a preference and prey handling study of sub-adult mitten crabs collected from the Thames. A digital camcorder, capable of detecting infrared light, was used in the laboratory overnight to identify crab food preference, document prey handling times and record behaviour. The test prey species, namely the amphipod Gammarus zaddachi, and two species of gastropod molluscs, Theodoxus fluviatilis and Radix peregra, were collected in the same habitat as the crabs and all were consumed under laboratory conditions. Eriocheir were able to capture mobile G. zaddachi using a novel prey capture technique not previously described in brachyurans and use different skills for handling each prey species. This flexibility in prey handling may be an important contributory factor in their freshwater invasive capacity. Results indicated that the crabs had a preference for G. zaddachi which were consumed most frequently and preferentially over both mollusc species. Prey choice may be based on maximising net energy gain as consuming G. zaddachi was shown to provide the highest rate of potential energy consumption by the crab due, in part, to a much shorter handling time than both species of snails.