Abstract
This paper reports the results of a ten-year monitoring program of an Atlantic Canadian population of green crabs, Carcinus maenas, in the Minas Basin of the Bay of Fundy. Intertidal densities, sex and reproductive ratios, juvenile recruitment, subtidal catch-per-unit-effort (CPUE), and sizes of crabs in this population were recorded from 2008 to 2017. In 2013 intertidal densities, mean crab sizes, subtidal CPUE, and proportions of crabs mature and reproducing all dramatically decreased to all-time lows, and large crabs virtually disappeared from the population. From 2014 to 2017 the population partially recovered but remained in an altered state. Potential causes of interannual changes to this population were investigated by correlating intertidal densities to 257 monthly environmental variables and performing stepwise multiple regression analyses. Crab densities in a given year were best explained by potential settlement during the summer and the maximum sea-surface temperature during March of the same year. However, potential roles of other factors (e.g., autumn winds, summer temperatures, North Atlantic Oscillation index) could not be ruled out. Changes in abundances of other species in the area, particularly predators and prey of green crabs, have also been observed and present possible alternative causative agents that should be investigated. Populations of other marine species in the Gulf of Maine-Bay of Fundy region within which the Minas Basin is situated have also been reported to have undergone dramatic changes in and after 2013, suggesting the occurrence of some oceanographic event or regime shift in the region. Declines to the monitored crab population in this study may have resulted from this same 2013 event. These observations have implications for recruitment to marine populations in this region.
Highlights
Detailed observations over time made on organisms of the same species in one or more selected locations, constituting the same putative ‘population(s)’, is a staple of studies in marine biology and ecology in general (Bertness et al, 1992; Santos & Simon, 1980; McGaw, Edgell & Kaiser, 2011; Palumbi & Pinsky, 2014)
This paper describes the results of efforts to monitor an established invasive population of green crabs (Fig. 1A) at Clarke Head, Nova Scotia (NS), Canada (Figs. 1B, 1C), within the Minas Basin of the upper Bay of Fundy (Fig. 1D)
There is much evidence that is suggestive that some sort of physical oceanographic and/or climatic event occurred in or around 2013 and impacted marine biota in the Bay of Fundy and Gulf of Maine, and this should certainly be investigated further
Summary
Detailed observations over time made on organisms of the same species in one or more selected locations, constituting the same putative ‘population(s)’, is a staple of studies in marine biology and ecology in general (Bertness et al, 1992; Santos & Simon, 1980; McGaw, Edgell & Kaiser, 2011; Palumbi & Pinsky, 2014) Such monitoring can provide essential information about the life history and demography of the species of interest. These observations provide information that can potentially be used to forecast longer-term impacts of such changes into the future, which is essential for management and conservation of marine species (Ruth & Berghahn, 1989; Pinsky et al, 2013; Wahle & Carloni, 2017)
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