Horizontal and vertical variations in survival rates of juvenile bivalves, Anadara kagoshimensis (Tokunaga, 1906), Ruditapes philippinarum (Adams & Reeve, 1850) and Atrina sp., experimentally caged in the inner area of the Sea of Ariake, Japan

Abstract

In the inner area of the Sea of Ariake, rearing experiments were conducted to examine how the survival rates of juveniles of three bivalve species (<em>Anadara kagoshimensis</em>, <em>Ruditapes philippinarum</em>, <em>Atrina</em> sp.) vary among sea areas and heights above the seabed. In three runs of the experiment, replicate samples of the three bivalves were kept in trays set at various heights above the seabed (range 0–40 cm) at one to six stations for 15–16 days. Results were as follows. (1) Survival rates varied among heights and stations more markedly for <em>Atrina</em> sp. than for <em>A. kagoshimensis</em> and <em>R. philippinarum</em>; (2) <em>Atrina</em> sp. always showed higher survival rates at greater heights above the seabed, whereas the other species did not always show this pattern. (3) Survival rates of <em>Atrina</em> sp. showed a different station-to-station variation pattern between experimental runs. (4) In statistical model selection, the spatial variations in the survival rate were not associated for either <em>A. kagoshimensis</em> or <em>R. philippinarum</em> with any of the environmental factors recorded (density of suspended solids, density of chlorophyll <em>a</em>, water temperature). In contrast, for <em>Atrina</em> sp. they were strongly and negatively associated with the spatial variations in density of suspended solids.