Nursery function of Wadden Sea tidal flats for the brown shrimp Crangon crangon

Abstract

The significance of the tidal zone as nursery area of the brown shrimp C. 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 are 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 Feb.-Aug. with main arrival during April, May and June; it leaves the tidal zone, at a body length of ca. 30 mm, during July-Sept. 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 are explained by the seasonal temperature cycle and its effect on the development of the juveniles at this 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.