Zooplankton species composition in the Oosterschelde (SW Netherlands) before,during and after the construction of a storm-surge barrier

During the period of construction of a storm-surge barrier current velocities decreased strongly and the Eastern compartment of the basin obtained a lagoon-like character. The rotifer Synchaeta spp., already abundant in the neighbouring salt and brackish lakes, profited from this condition. Higher and less fluctuating salinities caused the estuarine character of this compartment to disappear in the post-barrier years. This was reflected in the obscured succession of some Acartia species: the estuarine A. tonsa dominated in pre-barrier- and barrier years during summer, while the marine A. clausi was abundant in the post-barrier Oosterschelde during that time. Also the changed food conditions (Bakker & Vink, 1993) may have played a role in this phenomenon.Further changes in species composition were hardly observed. The main changes were of a quantitative nature (Bakker & Van Rijswijk, 1993; Tackx et al., 1993). A list of the commonly occurring species is given.