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.

The European green crab, Carcinus maenas, is an extremely successful species worldwide. C. maenas was first recorded in Nova Scotia in 1953, and by the 1990s it was found in the Bras d'Or Lakes in Cape Breton. Adults of C. maenas can tolerate salinities as low as 4. However, their larvae are not known to survive in salinities below 20 in their native range. High abundances of adult and juvenile C. maenas, as well as zoea-1 larvae and megalopae, are recorded in the Bras d'Or Lakes, where surface salinity may rarely exceed 20. It is possible that the early zoeal stages are more tolerant of lower salinities than those from their native habitat. Alternatively, they may have developed a tolerance for short-term exposure to low salinities. To examine the long-term tolerance of early zoeal stages (zoea-1 and zoea-2) of C. maenas to different salinities, newly released larvae from females from the Bras d'Or Lakes were individually reared in the laboratory at four practical salinities (14, 17, 20, 26). Larval survival decreased sharply and larvae did not develop past zoea-1 in salinities of 14 and 17, while larvae reared at a salinity of 20 did not survive past zoea-2 and larvae reared at a salinity of 26 completed development to the megalopa stage. Variation in larval survival among females was greatest at 26 and decreased with decreasing salinity. To examine the short-term tolerance of early zoeae, newly released zoeae were initially placed in a salinity of 14 for 1 day or 20 for 3 days, before being transferred to a salinity of 26. Larval survival did not increase and development did not resume after larvae were transferred to the higher salinity. These results suggest that early larval stages of C. maenas from the Bras d'Or Lakes are not adapted to either long, or short-term exposures to the low salinities typical of the surface waters of the Lakes. It is possible that these larvae may be able to tolerate exposure to low salinity water for shorter periods than those examined, or that they are behaviourally avoiding waters of low salinity in order to survive in this invaded habitat. RÉSUMÉLe crabe vert européen, Carcinus maenas est une espèce extrêmement répandue dans le monde. C. maenas fut pour la première fois signalé de Nouvelle-Ecosse en 1953, et dans les années 1990,