Drastic decline of an extensive eelgrass bed in Nova Scotia due to the activity of the invasive green crab (Carcinus maenas)

The European green crab, Carcinus maenas, is an invasive species in eastern North America and has the potential to significantly impact wild and aquaculture shellfish in the southern Gulf of St. Lawrence, Canada. To examine potential predation effects on local shellfish and assess the appropriateness of extrapolating results from studies conducted elsewhere, the morphometry of chelae from a recently established population of C. maenas in Nova Scotia was examined for comparison with the presumed founding (European) population, and forces generated by the chelae over a range of crab sizes were estimated. The Nova Scotia population was found to be morphologically very similar to European populations with respect to chela structure. Force generation by the chelae was found to scale with isometry in the female crab and with positive allometry in the male. Estimated forces compare well with previously reported forces, and force generation is calculated to increase in a nonlinear manner proceeding from the chela tips proximally toward the fulcrum. The calculated forces generated by the chelae are clearly sufficient for outright crushing of some shells (e.g., Mya arenaria), even for small crabs, but appear to be too low for crushing those of other molluscs. There is a complex interplay between gape and maximum force along the length of the dactyl that allows great variability in force application, and thus also in the size of prey consumed and prey-handling behaviour. We suggest that for such a lever system, the gape angle of the chelae, which does not change with crab size, is optimal with respect to the resultant force generated.

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Invasive green crab, Carcinus maenas, on the Atlantic coast and in the Bras d'Or Lakes of Nova Scotia, Canada: larval supply and recruitment

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s002531540501180x ◽

2005 ◽

Vol 85 (4) ◽

pp. 847-855 ◽

Cited By ~ 11

Author(s):

Beth Cameron ◽

Anna Metaxas

Keyword(s):

Nova Scotia ◽

Atlantic Coast ◽

Carapace Width ◽

Carcinus Maenas ◽

Green Crab ◽

Larval Supply ◽

Surface Salinity ◽

Life History Stages ◽

European Green Crab ◽

Tidal Signal

Patterns in larval supply and recruitment of the invasive European green crab, Carcinus maenas, were examined at two sites in Nova Scotia, Canada: a typical Atlantic coastal site with high salinity (∼33) and strong tidal signal (Terence Bay); and a microtidal site in the Bras d'Or Lakes, where surface salinity fluctuated from 0 to 23 (Benacadie Pond). Abundance of all life history stages (zoeae, megalopae, juveniles and ovigerous females) was sampled approximately biweekly at each site from June 2001 to June 2002. The reproductive season, based on the presence of ovigerous females, is ∼5 months (June to October) at both sites. Zoeae-I were collected from June to July 2001 and in June 2002 at Terence Bay, and from June to August 2001 at Benacadie Pond. We did not collect later zoeal stages at either site. Megalopae were collected from September to October 2001 at Terence Bay, and from August to September 2001 at Benacadie Pond. Juveniles 1–6 mm carapace width (CW) were present throughout the summer at Terence Bay, and only in autumn at Benacadie. Juveniles 6–12 and 12–27 mm CW were present throughout the summer and autumn at both sites. At Terence Bay, densities of 1–6 and 12–27 mm CW juveniles did not vary among intertidal zones. In contrast, the 6–12 mm CW size-class appeared to move higher in the intertidal through the season, possibly due to effects of predation.

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Absence of recovery in a degraded eelgrass (Zostera Marina) bed in Nova Scotia, Canada: Results from a transplant study

Proceedings of the Nova Scotian Institute of Science (NSIS) ◽

10.15273/pnsis.v50i2.10001 ◽

2020 ◽

Vol 50 (2) ◽

pp. 251

Author(s):

Erin Wilson ◽

David J. Garbary

Keyword(s):

Nova Scotia ◽

Zostera Marina ◽

Light Attenuation ◽

Carcinus Maenas ◽

Control Site ◽

Green Crab ◽

Eastern Canada ◽

Growth And Survival ◽

Negative Effect ◽

European Green Crab

By the early 2000s, the invasion of the European green crab (Carcinus maenas) had caused a severe decline of eelgrass (Zostera marina) beds in eastern Canada. The formerly lush eelgrass bed in Benoit Cove, Nova Scotia, was extirpated by 2009 and has subsequently failed to recover. The objective of our study was to establish if Benoit Cove (BC) has reached a new equilibrium in which eelgrass cannot recolonize. From July 3 - August 29, 2018, we transplanted eelgrass using frames and monitored eelgrass growth and survival relative to the nearby donor (control) site in Tracadie West Arm (TWA) that had an extensive eelgrass meadow with over 95% cover. Transplant survival was 91.6% and 15.4% for TWA and BC, respectively (P < 0.001). Above-ground growth declined at both sites, and could be associated with high summer water temperatures and/or extreme epiphytism. Sediments at both sites had high silt composition (> 28%), and the absence of a macrophyte canopy lead to increased light attenuation in BC in moderate wind and tidal currents. The low density of green crabs in both BC and TWA (0.01 m-2 and 0.08 m-2, respectively), and the apparently healthy eelgrass bed in TWA, suggest that green crabs are not having a negative effect on eelgrass in this system and are not responsible for the lack of recolonization of eelgrass in BC.Keywords: Atlantic Canada; eelgrass bed; European green crab; transplant; Zostera marina

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