A comparison of predation rates by non-indigenous and indigenous crabs (Juvenile Carcinus maenas, juvenile Cancer irroratus, and adult Dyspanopeus sayi) in laboratory and field experiments

Mean daily consumption rates on Mytilus spp. were compared among juveniles of the non-indigenous Carcinus maenas, juveniles of the indigenous Cancer irroratus, and adults of the indigenous Dyspanopeus sayi between June and August 2005 to assess the relative impact of juvenile C. maenas in field (Benacadie Channel (45 degrees 54' N, 60 degrees 53' E), Bras d'Or Lakes, Nova Scotia, Canada) and laboratory experiments. This study examined: (1) whether consumption rates in a field setting vary among species; (2) the effect of laboratory and field settings on species-specific consumption rates, and whether rates vary between settings for each species; and (3) the effects of temperature and salinity on the consumption rates of these species. In field experiments, there was no significant difference in consumption among C. maenas, C. irroratus, and D. sayi (0.100 +/- 0.067, 0.450 +/- 0.189, and 0.800 +/- 0.423 mussels crab(-1) d(-1), respectively). However, both C. maenas and C. irroratus consumed two to four times more prey in the laboratory than in the field. D. sayi prey consumption was also greater (although not significant) in the laboratory than in the field. In the laboratory, consumption rate was greater for C. irroratus in salinities of 26 than 17 (2.75 and 1.69-1.81 mussels crab(-1) d(-1), respectively), and in 17 degrees C than 13 degrees C (1.10-1.21 and 0.56-0.64 mussels crab(-1) d(-1), respectively) for C. maenas. In all experiments, consumption rates of juvenile C. maenas were lower than or similar to those of the juvenile and adult indigenous species, suggesting that the potential predatory impact of juvenile C. maenas on Mytilus spp. may not be as significant as that of the adults of this non-indigenous species.