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COMPARISON OF RECURITMENT FREQUENCY AND GROWTH OF SURFCLAMS, SPISULA SOLIDISSIMA (DILLWYN, 1817) IN DIFFERENT INNER-SHELF HABITATS OF NEW JERSEY
Citation:
Chintala, M AND J. P. Grassle. COMPARISON OF RECURITMENT FREQUENCY AND GROWTH OF SURFCLAMS, SPISULA SOLIDISSIMA (DILLWYN, 1817) IN DIFFERENT INNER-SHELF HABITATS OF NEW JERSEY. JOURNAL OF SHELLFISH RESEARCH 20(3):1177-1186, (2001).
Description:
Spisula solidissima (Dillwyn, 1817) populations along the U.S. East Coast reflect episodic settlement and recruitment success. An analysis of growth bands in the shells of 1,005 surfclams collected from nine zones within 3 miles of the coast of New Jersey in 1993 revealed years of good recruitment, and allowed the construction of growth curves for each zone. The 1988 year class predominated in most areas, comprising 53.5% of all clams sampled, followed by the 1996 year class (8.3%), and the 1983 year class (5.0%). In the zones located farthest north, 3- to 5-year classes each represented at least 10% of the samples. All of the zones south of Barnegat Inlet were dominated by the 1988 year class, which accounted for 45% to 95% of the clams within these zones. The temporal patterns of recruitment across miles zones, depth gradients, bottom types, or catch densities did not appear to be significantly different. There was considerable variation among the growth curves for surfclams along the coast. An examination of the shell height at age 5 (H5) for the 1988 year class in the northern and southern zones supports earlier findings that surfclams farther inshore grow more slowly and reach a smaller maximum size than clams farther offshore. The fact that the expected mean height at age one (H1) for the 1988 year class was the same throughout all zones suggests a single, widespread settlement event along the coast in that year. An analysis of U.S. EPA surface and bottom temperature data (1979-1991) indicated that mean temperature for summer 1988 was lower than for all other years in the six northern zones, and was also relatively low in the three southern zones. Lower mean summer seawater temperatures are correlated with a higher frequency and persistence of coastal upwelling events, which in turn are associated with high larval abundances in the downwelling that immediately follows each upwelling. Thus, high recruitment may be the consequence of these hydrodynamic effects on larval supply, in addition to the effects of cool bottom temperatures in reducing predator impacts on recently settled surfclams.