Reproductive periodicity and larval vertical migration behavior of European green crab Carcinus maenas in a non-native habitat

Abstract

The reproductive periodicity and vertical migration behavior of the European green crab Carcinus maenas in a non-native environment were characterized and the implications for invasion dynamics highlighted. Biweekly to monthly trap surveys in Pipestem Inlet, British Columbia, revealed ovigerous crabs from mid-February to June 2007. Concurrent meroplankton surveys confirmed green crab zoeae by mid-April, about 1 mo following peak abundance of ovigerous crabs (March 2007). All 4 zoeal stages of development were sampled between March and December 2007, but >95% were Stage I zoeae sampled between April and August. Vertical meroplankton surveys conducted in 2008 revealed diel-mediated vertical migratory (DVM) behavior; however the majority of sampled zoeae were aggregated near the pycnocline in surface outflowing waters. Negligible densities of post-Stage I zoeae (<1%) support the observation of zoeal export from Pipestem Inlet. Tidal-mediated vertical migratory behavior, characteristic in native European populations, was not observed in Pipestem Inlet. In contrast, low larval densities were sampled in surface (<1 m) and deep (>8 m) sampling strata. We hypothesize that low surface salinity (17-19 psu) and cold temperature (<12°C below the pycnocline) in deep strata constrained DVM. Our results highlight a need for better characterization of reproductive periodicity and zoeal migratory behavior in non-native habitats, which has implications for improving predictions of secondary spread and range expansion rates mediated via larval dispersal dynamics.