Metal concentrations and year-class structure of a wedge clam Latona cuneata.

Abstract

The relations between metal contents or concentrations, and year-class structures of soft and hard compartments and whole body were discussed for some heavy metals in the wedge clam Latona cuneata collected from the exposed sandy tidal zone of Nagahama that is located in the west coast of Tanegashima free from any pollution under the influence of Kuroshio. Before determination of metal contents, the consecutive sampling for wedge clams was carried out for over three years, and biological informations; such as, year-class group and its structure, sexual maturation, main spawning age group, spawning season, tidal migrating habit, etc. were gathered. Generally, plotting metal contents against three body weights (soft body, conch and whole body) of the wedge clams on a double logarithmic diagram produced regressive relationships with two or three straight lines. The critical points of regression slopes for Fe, Zn, Cu and Mn in soft compartment were found and fell into two categories: two slopes and one critical point for Fe, Zn and Mn that were situated in the range of μ to μ+Ó of the first year-class; three slopes and two points for Cu situated at the range of μ-Ó of the first year-class and around μ of the second year-class. These results differed greatly from single straight line relationships for several elements in a variety of marine and estuarine molluscs reported by several researchers. The critical points which appeared in the soft compartment could be related to reproductive activity, i. e. for Fe, Zn and Mn the members of main spawning group, the second year-class, set out to be mingled from the paint that was situated in the range between μ and μ+Ó of the first year-class. Before and after the beginning of the mixture of members of the first and those of the second year-classes the slopes were reversed from negative to positive. Concentrations of Cu in main spawning group paralleled the X axis, and in the extremes the slopes were reversed from positive to negative.