Reduced epibenthic predation on intertidal bivalves after a severe winter in the European Wadden Sea

Abstract

One hypothesis to explain the phenomenon of high bivalve recruitment after severe winters in coastal North Sea sediments is reduced epibenthic predation. Using predator exclusion experiments, I tested the hypothesis that epibenthic predation on the juvenile bivalves Cerastoderma edule, Macoma balthica and Mya arenaria was lower after a severe winter (1995 to 1996) than after a moderate (1996 to 1997) and a mild (1997 to 1998) winter. In C. edule and M. arenaria there was 2-fold evidence for reduced epibenthic predation after the severe winter: (1) significant predation effects occurred only in exclusion experiments after the 2 milder winters but not after the severe winter; and (2) recruits attained larger sizes in August and October after the severe winter suggesting continuous growth rather than truncation of the size spectrum by predators. In M. balthica, predation effects were also significant only after the milder winters but there was no effect on size. In all 3 bivalve species, recruitment at the experimental sites in the fall was higher after the severe winter than after the 2 milder ones. These results suggest that high bivalve recruitment after severe winters is primarily caused by the post-settlement factor of reduced epibenthic predation on the tidal flats. The strategy to conduct several predator exclusion experiments in both sand and mud in 3 consecutive years with differential winter conditions, and while considering migration activity and size development in juvenile bivalves, proved useful to distinguish between cage artefacts and predation effects.

Sediment destabilizing and stabilizing bio-engineers on tidal flats: cascading effects of experimental exclusion

“…In these bivalves, mucus threads several times the length of the animals enable them to become eVectively transported in the water column by currents (Sigurdsson et al 1976;Beukema and de Vlas 1989;Armonies 1996). Due to these secondary redistributions species are able to colonise habitats which are more suitable for subsequent life stages (Armonies 1994;Strasser 2002;Hiddink 2003). After having burrowed between polychaete tubes, the juvenile bivalves may additionally Wnd shelter from predation and the likelihood of re-suspension may be reduced (Armonies and Hellwig-Armonies 1992).…”

Predation and habitat modification synergistically interact to control bivalve recruitment on intertidal mudflats

“…For instance, lowered hydrodynamic intensity in the cages may lead to reduced sediment disturbance, in turn enhancing larval settlement (Strasser, 2002). Nevertheless, our analyses revealed little evidence of cage artefacts.…”

“…Cages were similar in design as those used by Strasser (2002) near Sylt in the German Wadden Sea, but with a larger surface area. The cages were cylindrical with a 32-cm diameter and a height of 30 cm.…”

“…Apart from environmental factors (e.g., temperature, hydrodynamics, substrate conditions), it has been suggested that biotic interactions like chemical cues are important to initiate settlement (Dobretsov and Wahl, 2001;Liu et al, 2011). Once settled, overall recruitment success of bivalves in intertidal areas is considered to be depend on many different factors, including abiotics, predation and facilitation effects (van der Veer et al, 1998;Brinkman et al, 2002;Strasser, 2002;Schulte et al, 2009;Troost, 2010). Our experimental findings suggest that these factors are not only important, but that they can strongly interact to control bivalve recruitment dynamics, potentially explaining in part the difficulties in predicting bivalve recruitment success in soft-sediment systems.…”

“…In this study, we therefore investigated the importance of predation, habitat modification and their interplay in explaining bivalve recruitment dynamics in the intertidal of the Wadden Sea. Predation during high tide by brown shrimp (Crangon crangon) and shore crab (Carcinus maenas) has been suggested to have a strong negative effect on bivalve recruitment in soft-sediment systems (van der Veer et al, 1998;Strasser, 2002). Next to predation, biotic habitat modification could be an important driver for recruitment as well, because such mechanisms can cause strong facilitation effects in coastal ecosystems (Bruno et al, 2003;Eriksson et al, 2010).…”