In the Wadden Sea, heavy metals representa long-term risk for organisms. Therefore, we investigated spatial and temporal variation ofPb, Hg and Cd contents in benthic organistas. Considering the high va¡ ability of individual condition and size of the bivalve Cerastoderma edule and the polychaete Nereis diversicolor, it was only partly possible to estimate different bioavailabilities. Organisms, as well as some sediment samples, were collected at six sampling sites in the backbarrier area of the East Frisian island of Spiekeroog, Germany. According to both species, the results indicated similar microgeographic pattems. Additionally, data pointed to a higher bioavailability ofPb and Hg at the coastal, fine grained sampling sites than at the other stations. Therefore, the spatial variability seemed to coincide more with the sediment composition than with the spatially, rather homogeneous, contamination of the pelitic fraction (<20 gm grain size). Respecting the temporal variation between November 1992 and November 1994, samples of animals resulted in relatively high levels ofheavy metals in spring and low ones in summer, which coincided with intrinsic, temporal rest¡ factors such reproduction, food intake and others. The results gaste hints for optimizing monitoring concepts.

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