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Larval immigration and subsequent settlement, abundance fluctuations, growth, and mortality of a 0-group flounder population were studied in a tidal flat area, the Balgzand, in the western Wadden Sea. Larvae entered the area from early April to early May. The first settled flounder were found about 1 mo after larval immigration started. Settled flounder were restricted to the siltier areas of the tidal flats. Growth did not seem to be food-limited within the density range observed over the years and depended only on prevailing water temperatures. The life history pattern of flounder was similar to that of plaice in the same area: year-class strength was generated in the open sea and after settlement a period of density-dependent mortality followed, most probably due to predation by crustaceans. The instantaneous mortality rate Z during summer seemed to be higher (0 08 d-l) than in plaice (0.03 dC1), probably due to a combination of higher water temperature and higher abundance of predators in summer than during the settlement of plaice in spring. No relationship between the year-class strengths of plaice and flounder was found

The significance of the tidal zone as nursery area for the brown shrimp Crangon crangon became evident during a study on density and size-distribution of predator populations on a 50 km2 tidal flat in the western Wadden Sea (The Netherlands). A clear picture of the nursery system and its function in the annual cycle of brown shrimp is obtained when nursery population-data are combined with experimental growth rates in juvenile C. crangon and their dependence on temperature and body size. Shrimp brood settles in the area during February-August with main arrival during April, May and June; it leaves the tidal zone, at a body length of ca. 30 mm, during July-September. At the end of the year the majority of the new shrimp generation reaches maturity, after which winter spawning leads to settlement of new brood in spring again. The annual cycle thus obtained fits well in the seasonal pattern of commercial shrimp catches in the area. The predominance of winter spawning and the low effect of summer-egg production is explained by the seasonal temperature cycle and its effect on the development of the juveniles at our latitude, as well as by a specific seasonal pattern of predation pressure on shrimp brood in the tidal zone. Spawning cycles in C. crangon along other parts of the European continental coast are discussed

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