. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SEA SCALLOP GROWTH RATES 187 Taylor and Venn, 1978; Serchuk et al., 1979; Paul, 1981). Scallops deposit calcium carbonate in the form of calcite to the shell margin in concentric increments. During the warmer months of the year, while the scallops are growing rapidly, the distance between consecutive increments is relatively wide (Stevenson and Dickie, 1954; Mason, 1957; Taylor and Venn, 1978). As growth slows during the winter and early spring, the growth increments are crowded together, forming what appears to be a concent
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SEA SCALLOP GROWTH RATES 187 Taylor and Venn, 1978; Serchuk et al., 1979; Paul, 1981). Scallops deposit calcium carbonate in the form of calcite to the shell margin in concentric increments. During the warmer months of the year, while the scallops are growing rapidly, the distance between consecutive increments is relatively wide (Stevenson and Dickie, 1954; Mason, 1957; Taylor and Venn, 1978). As growth slows during the winter and early spring, the growth increments are crowded together, forming what appears to be a concentric line or ring on the shell (Fig. 1). The interpretation of external lines as representing years of growth for an individual specimen is often complicated by numerous disturbance or shock rings. Sea scallops are notably sensitive to physical disturbances and sudden changes in environmental conditions such as sharp temperature or salinity changes, or storm-related turbulence (Merrill et al., 1965). In response to strong stimuli, scallops retract the mantle and cease calcification along the shell margin. This action leaves a noticeable line after shell growth resumes. Distinguishing annual lines from disturbance lines macro- scopically is frequently difficult and often very subjective (Stevenson and Dickie, 1954; Merrill et al., 1965). Other shell characteristics, such as seasonal variation in shell color, convexity of the shell profile, and activity of boring organisms, may provide some information for the interpretation of external lines (Merrill et al., 1965). However, these additional methods are still very subjective and are not conclusive. In view of the uncertainties involved in the accurate interpretation of growth rings, additional methods of establishing the periodicity of these features have been pursued in other species of molluscs. Principal among these efforts has been the investigation of stable isotope variations across shell increments {, Yavnov and Ignat'e
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