Settlement and Recruitment Patterns of the Soft-Shell Clam, Mya arenaria, on the Northern Shore of the Bay of Fundy, Canada

Abstract

To examine the roles of settlement and early postsettlement processes in the recruitment of the soft-shell clam, Mya arenaria, abundance of recent settlers and juveniles was monitored over two field seasons at four locations on the northern shore of the Bay of Fundy in New Brunswick, Canada. Results showed great spatial and temporal variability in patterns of settlement. M. arenaria appeared to become highly vulnerable to postsettlement processes at a shell length of approximately 2 mm. Postsettlement processes drastically altered patterns of settlement less than 1 year after they were established. Results suggest that local factors at specific sites within the Bay of Fundy, such as hydrodynamics, larval behavior, and early postsettlement events, likely control the abundance of juvenile clams. Additionally, postsettlement events are extremely important in shaping M. arenaria populations in this area. Very few mature adult clams greater than 50 mm in shell length were found at any sampling sites, and no relationship was found between abundance of setters and density of juveniles and adults.

Cohort life tables for a population of the soft-shell clam, Mya arenaria L., in the White Sea

“…Sharp dominance of individual generations for several years proved to be true for other beds both in the White Sea (Sadykhova 1982;Gerasimova and Maximovich 2013) and in other parts of their geographic range (Commito 1982;Strasser et al 1999Strasser et al , 2003. The predominance of a single generation was explained mainly by interannual shifts in recruitment level (Commito 1982;Strasser et al 1999Strasser et al , 2003Flach 2003;Bowen and Hunt 2009). Causes of fluctuations in recruitment level of Mya arenaria have been repeatedly discussed by different researchers including the authors of this study (Brousseau 1978;Commito 1982;Sadykhova 1982;Günter 1992;Maximovich and Guerassimova 2003;Gerasimova and Maximovich 2013).…”

“…It was noted that the highest mortality was observed in the first years of life, while the next ontogenetic stages were characterized by a relatively high survival (Brousseau 1978;Commito 1982;Brousseau and Baglivo 1988). Most researchers pointed that predation was the main reason for high mortality at early stages (Beal et al 2001;Strasser and Günter 2001;Beal and Kraus 2002;Strasser 2002;Flach 2003;Strasser et al 2003;Beukema and Dekker 2005;Beal 2006a;Bowen and Hunt 2009). Along the Atlantic coast of North America, the most common predators of juvenile Mya are gastropod Euspira heros and crustacean Carcinus maenas (Commito 1982;Beal et al 2001;Beal 2006a, b).…”

Evidence of selection for resistance to paralytic shellfish toxins during the early life history of soft‐shell clam, Mya arenaria, populations

“…Blooms of Alexandrium fundyense in the Bay of Fundy are initiated in late May to early June and persist through the summer until mid-to late September, with peak cell densities up to 162 cells mL 21 occurring in mid-July (Martin et al 1998(Martin et al , 2009). Soft-shell clam settlement peaks in the region typically occur from mid-August to mid-September (Emerson and Grant 1991;Bowen and Hunt 2009). The peak of shellfish toxicities, and thus the timing of toxic blooms, occurs earlier in a southwestward direction along the coast from eastern Maine to Cape Cod, partly reflecting earlier coastal warming and stratification in the western region (Anderson 1997;McGillicuddy et al 2005).…”

Loss of Eelgrass in Casco Bay, Maine, Linked to Green Crab Disturbance

“…Because clams along the upper shore grow more slowly than at lower tidal levels (Beal et al, 2001), and are significantly older than individuals lower on the shore (Powers et al 2006), clammers now are benefitting from a cumulative subsidy of years of commercial inactivity at upper shore levels. Because natural recruitment of Mya is highly variability throughout its range (Hunt et al, 2003;Bowen and Hunt, 2009;Vassiliev et al 2010;Morse and Hunt, 2013), at current exploitation rates, it is unclear how long softshell clams in Freeport and other southern Maine communities will remain a viable commercial industry.…”