Seasonal Variation and Inherent Variability of Trace Elements in Oysters and Their lmplications for Indicator Studies

Abstract

The seasonal variation in concentrations and body burdens of 8 trace elements in C. gigas was investigated, using individuals transplanted from Menar Strait in Wales to 2 Cornish estuaries. Seven of the 8 elements exhibited generally similar profiles for concentration, maxima occurring in winter and minima in summer. Some differences were noted in profiles for body burdens of these elements, depending on the loss of metals with gametes at spawning or on the rate of element uptake during autumn and winter. However, in each case, seasonal variation in concentration of the element was defined largely by changes in the weights of the whole soft parts of oysters, which in turn were dependent on the gametogenesis-spawning cycle. The 8th element, manganese, exhibited quite different kinetics; tissue weights of the oysters were of much less importance in defining seasonality of this metal. The inherent variability of zinc levels in three populations of two species of oyster, C. gigas and Ostrea edulis , was also investigated to estimate the minimum number of individuals required to characterise element levels in an oyster population. The possible reasons and the implications of both inherent variability and seasonality of elements are considered with respect to using bivalves as biological indicators of metal abundance.