ANALYSIS OF THE SPATIAL VARIABILITY IN ABUNDANCE AND AGE STRUCTURE OF2 INFAUNAL BIVALVES, CERASTODERMA-EDULE AND C-LAMARCKI, USING HIERARCHICAL SAMPLING PROGRAMS

Spatial variability in abundance and age distribution of 2 infaunal bi valves, Cerastoderma edule (Linnaeus, 1785) and C. lamarcki (Reeve, 18 45), were quantified using hierarchical sampling programs. The scales investigated ranged between 100 and 10(5) m. Analyses of variance reve aled significant variability in abundance among sites within bays (sim ilar to 100 m apart) for both species and also among bays (similar to 1 km apart) for C. lamarcki. Mean age varied at several spatial scales . For both species, however, the scale contributing most to the variat ion was bays, which provided about 40 % of the total variation for eac h species. Randomization procedures were used to test the generality o f previous observations of non-random distributions of year classes (n amely number of year classes and dominance by single year classes). Th ese analyses showed that for both species a spatial unit contained sig nificantly fewer year classes and the most abundant year class was sig nificantly more abundant than expected by chance. These results were c onsistent for all spatial scales except among plots (similar to 10(1) m apart) in C. lamarcki. The necessity to assess spatial patterns at a wide range of spatial scales is emphasized. Potentially important pro cesses (focusing on larval supply and recruitment) which generate the observed patterns and general implications of spatial variability are discussed.