Comparison of different sampling strategies in monitoring zoobenthos and classification of archipelago areas

The European Water Framework Directive (EC WFD/2000/60) states that all coastal surface waters should achieve Good ecological status by the year 2015.For this purpose waterbodies have been classified, and a subsequent step is to establish monitoring and management plans for each waterbody.We assess what is an optimal, cost-effective sampling design in monitoring zoobenthos for WFD purposes in complex archipelago waters in the northern Baltic Sea.Zoobenthic grab samples were taken from three archipelago areas of different exposure, and the results of two different sampling methods were compared: the traditional replicate sampling method (3-5 replicate samples at each station) and a proposed single-sample method (no replicate samples).The choice of sampling strategy did not affect the general results on basic community parameters.The ecological status of the areas was somewhat over-estimated when the single-sample strategy was used.The replicate design turned out to be more cost-effective as it is less time-consuming in shallow archipelago areas, especially when small boats and hand-held equipment are used.Further, the replicate sample strategy was more conservative in assessing the ecological status, which may prevent too optimistic status classifications of specific waterbodies.