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°54′ N, 60°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°C than 13°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.
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 ), 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.
Predictive models used to determine the impacts of nonindigenous brachyurans on their “ecological equivalents” in marine ecosystems are sorely lacking. Determining the spatial and temporal extent and magnitude of such impacts by nonindigenous species is difficult because of the broad range of qualitative and quantitative criteria currently used to describe their effects. Forecasting potential impacts requires the development of predictive models that incorporate the effects of interspecific interactions and the mechanisms that give rise to these interactions. Successful validation of such models requires improved techniques for measuring and estimating the functional responses on bioenergetic processes across species compositions, abundances, and environmental conditions. Species-specific information used to support predictive modeling of nonindigenous brachyurans is currently heavily biased towards (i) estimating per capita consumption and growth rates in laboratory conditions and (ii) incorporating the effects of abiotic and biotic factors on these measures. Robust predictive models require repetitive experimentation that advances the understanding of species’ interactions (beyond consumption alone) across variable densities and considers their effects across different spatial and temporal scales.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.