Age and growth rate of the clam, Spisula solida L., from a site off Vilamoura, south Portugal, determined from acetate replicas of shell sections
M.B. Gaspar, M. Castro and C.C. Monteiro

The age and growth rate of a population of Spisula solida from Vilamoura, southern Portugal, were studied from acetate peel replicas of polished and etched shell sections. The growth pattern consists of alternating dark and light zones. During the winter, wide growth increments (light zones) are deposited, characteristic of rapid shell growth, whilst narrowly spaced growth bands with a small depression or cleft associated (dark zones) are formed in the summer between June and August. The annual shell increments were used to determine age and growth rate. Von Bertalanffy growth curves estimated from surface growth rings differed from the growth curve estimated using internal lines. When surface rings were used to estimate age of this species an overestimation of age and an underestimation of growth rate occurred. Field experiments showed that the periodicity of the microgrowth pattern is related to an endogenous rhythm of shell formation and not to exogenous factors. The growth curves obtained for both internal growth pattern (A) and surface rings (B) are: (A) Lt= 45.08 [1- e -0.43 (t+0.33)] (B) Lt= 50.22 [1- e -0.25 (t+0.33)]

Keywords: Bivalves, Clams, Spisula solida, growth, age determination, acetate peel.
Contents of this volume Sci. Mar. 59(Suppl.1) : 87-93 Back PDF
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