Eriocheir sinensis, (Crustacea: Decapoda, Brachyura, Varunidae): fish egg consumption

Dispersal of Eriocheir sinensis from its native habitat is a worldwide concern. As one of the most invasive species known, this crab causes significant disruption to foreign ecosystems. In particular, populations in the United Kingdom (UK) are increasing in number and E. sinensis has been reported from many river catchments (www.mittencrabs.org.uk). The ecological implications of this invasion are not fully understood. One aspect of concern lies in the potential for mitten crabs to predate fish eggs which, if realistic, could contribute to the decline of riverine populations. In this study, 100 mitten crabs from the River Thames were used in experimental feeding trials to 1) investigate foraging ability on a variety of fish eggs and 2) establish whether crab size affected foraging potential. Eggs ranged from 1-6 millimetres (mm) in diameter from one of four species of marine and freshwater fish; zebrafish, lumpfish, Pacific salmon and trout. Predation by crabs varied with egg type; crabs were capable of foraging 1mm zebrafish eggs, but the majority consumed eggs 2-6mm in diameter. The most attractive eggs were apparently lumpfish, where the median proportion consumed was 100%. Crab size did not appear to govern foraging potential, though variation was observed in the size range of juvenile crabs consuming the different eggs with the largest, salmon, being consumed by crabs of the broadest size range. E.sinensis does have the potential to predate on a range of fish eggs, and the results are used to infer the risk presented to specific groups of UK fish stocks.