Synchronized reproductive success in the main bivalve species in the Wadden Sea: causes and consequences

Abstract

This paper surveys data obtained during 3 decades of monitoring the macrobenthic fauna of a 50 km 2 tidal-flat area in the Wadden Sea (Balgzand) and compares the annual figures with similar long-term data series from other parts of the Wadden Sea (Groningen, Norderney). Despite enormous year-to-year variability in annual recruitment of particularly the bivalves, totalbiomass values were remarkably stable. Detailed data are presented on the annual variability in recruitment success of the 4 most important bivalve species of the Balgzand area (Cerastoderma edule, Macoma balthica, Mya arenaria, and Mytilus edulis). Together these 4 species usually accounted for more than half of the total zoobenthic biomass and largely governed its year-to-year fluctuations. Recruit numbers of the 4 species observed in 27 summers showed similar relationships with the character of the foregoing winter. Such relationships were also observed in other Wadden Sea areas in The Netherlands and Germany. These common relationships resulted in a certain synchrony of recruitment success between the species (within areas) and between areas (within species). Thus, over vast areas (hundreds of km), bivalve recruit densities were generally (though not invariably) high after severe winters and low after mild winters. The resulting strong year-to-year variability in recruit numbers (with standard errors exceeding long-term means) was only just passed on to subsequent total-biomass values for the following 3 reasons: (1) the biomass of any species was generally composed of more than 1 year class, (2) the various species did not reach their maximal biomass at the same age (time elapsed after recruitment), and (3) feedback mechanisms (enhanced reduction of numbers at high abundance) were effective in some species.

The effect of eutrophication abatement on the bivalve Scrobicularia plana

“…Nevertheless, only a single new cohort could be distinguished each year. Moreover, like other bivalve species (Beukema et al, 2001), recruitment was more intensive after a severe winter (e.g. 1994), and subsequent years were often characterised by lesser recruitments.…”

Differential recruitment of bivalve species in the northern Wadden Sea after the severe winter of 1995/96 and of subsequent milder winters

“…At least part of this variation appears to be closely related to winter temperature. The four most common bivalves in the Wadden Sea, Cerastoderma edule, Macoma balthica, Mya arenaria, and Mytilus edulis, all showed generally higher recruitment after severe than after mild winters (Beukema 1992a;Beukema et al 2001). While recruitment may be close to zero in some years, exceptionally high abundances in the order of 10 4 -10 5 individuals (ind) m -2 appear to be common on the tidal flats of the Wadden Sea after severe winters.…”

“…Similar results were reported after the winter of 1978/79 in the German and Dutch Wadden Sea (Reichert and Dörjes 1980;Beukema 1982;Reise 1987;Obert and Michaelis 1991). Analysis of long-term data from the Dutch Wadden Sea revealed that abundances of Cerastoderma, Macoma, Mya, and Mytilus peaked synchronously after severe winters (Beukema 1992a;Beukema et al 2001).…”

“…In the intertidal Wadden Sea, bivalves show huge annual variations in recruitment success (Beukema 1982(Beukema , 1992aBeukema et al 2001). At least part of this variation appears to be closely related to winter temperature.…”

Cold winter effects on benthic macrofauna communities in near- and offshore regions of the North Sea

“…But these changes were based mainly on a highly successful recruitment of echinoderms in 1996, which is known to be patchy (Ò lafsson et al 1994;Thie´baut et al 1998), and not by a decrease in abundance or number of species. Highly successful recruitment after cold winters was found for several benthic species (Do¨rjes et al 1986;Beukema et al 2001;Kro¨ncke et al 2001;Strasser et al 2003). However, since most benthic species disperse via pelagic larvae, local recruitment is often decoupled from local reproduction (Bosselmann 1991;Caley et al 1996;Eckert 2003).…”