SMALL-SCALE VARIABILITY OF BIOCHEMICAL INDEXES OF GROWTH IN MYA-ARENARIA (L)

The small-scale variability of biochemical indices of growth (RNA:DNA, protein:DNA, and protein:RNA) was investigated in the gills, adductor muscle, and digestive gland of the intertidal bivalve Mya arenaria (L .). Field and tank experiments were conducted in order to determine th e effect of age and body size on the indices, and to assess the spatia l variability of the indices and their rapidity of response to emersio n. The protein:DNA and protein:RNA ratios of the gills and the digesti ve gland varied positively with the animal's age or size while the bio chemical indices of the adductor muscle were not affected by these par ameters. An important spatial variability was observed. The indices of the adductor muscle were significantly different among animals collec ted within a sampling surface of 12.5 x 12.5 M2 but remained homogeneo us within 2.5 x 2.5 M2 quadrates. The protein:DNA ratio of the gills w as even more variable, being significantly different among animals col lected within a sampling surface of 2.5 x 2.5 m2. The indices were onl y slightly affected by emersion: they did not significantly vary until the clams had been exposed for at least 14 hours. This emersion indep endence probably reflects the adaptation of intertidal animals to thei r habitat, where they are regularly subjected to hypoxia.