Variability in predator abundance links winter temperatures and bivalve recruitment: correlative evidence from long-term data in a tidal flat

In the Wadden Sea, annual recruitmentin the major bivalve species is mostly successful insummers following severe winters, whereas it usuallyfails after mild winters. On the basis of a 40 yr data series,we corroborated this relationship between wintertemperatures and subsequent summer abundance ofrecruits in 3 bivalves: Macoma balthica, Cerastodermaedule, and Mytilus edulis. A 30 yr data series showedthat annual abundance of their main epibenthic predators(0-group shrimp Crangon crangon and 0- and 1-group shore crabs Carcinus maenas) was higher insprings after mild winters compared to cold ones. Summerrecruit numbers in 4 bivalve species (the aboveand Mya arenaria) were higher when predator biomasshad been lower in the preceding spring. We arguethat the latter relationship was probably of a causalnature and might explain not only the relationship betweenwinter temperatures and bivalve recruitmentsuccess, but also the observed synchronies of annualrecruitment success between bivalve species and betweendistant parts of the Wadden Sea. Shrimp abundancein May showed a significantly increasing longtermtrend that might partly explain the decliningtrends in recruitment success, biomass, and annualproduction observed in the western Wadden Sea inM. balthica and M. edulis.We conclude that top-downeffects by predation on early bottom stages of bivalvesstrongly affect biomass and production of some of themost important members of the benthic community ofthe Wadden Sea, keeping this system well below itscarrying capacity for bivalves in nearly all years