Overlap in the distributions between indigenous and non-indigenous decapods in a brackish micro-tidal system

Abstract

In the Bras d'Or Lakes, Nova Scotia, Canada, the vertical distributions and abundances of the non-indigenous Carcinus maenas and the indigenous Cancer irroratus and Dyspanopeus sayi were quantified at 4 sites (to a maximum depth of 3.5 m in 2005), in 3 seasons (spring, summer and fall), in each of 2 years (2005, 2006). All species overlap spatially and temporally at 0.5 m in all seasons and years, indicating a strong potential for biotic interactions (e.g. habitat use, prey consumption). All species, particularly the juvenile stages, were most abundant at shallow (≤1.5 m) depths and were strongly associated with cobble and cobble-composite substrates. C. maenas and D. sayi abundances were also strongly correlated at shallow depths in Benacadie, Ross Ferry and Kempt Head. In 2006, when winter water temperatures were ~1 to 4°C warmer than in 2005 (at which time winter water temperatures were <0°C and ice coverage was extensive), the abundances of C. maenas and D. sayi were ~1.5- to 10-fold higher, and pronounced pulses in recruitment were observed. The abundance of C. irroratus was low (<0.125 ind. m-2) in Benacadie (compared to C. maenas and D. sayi, at 0.5 to 10 ind. m-2), where salinity regularly falls below 20, a level which is outside the preference and tolerance of C. irroratus. Inter-annual differences in water temperatures may influence the survival and abundance of both indigenous and non-indigenous species, which could, in turn, modify biotic interactions among these species. © Inter-Research 2009.