The Birth, Growth and Death of Intertidal Soft-Sediment Bivalve Beds: No Need for Large-Scale Restoration Programs in the Dutch Wadden Sea

Abstract

Recruitment and fate of all 1436 mussel and oyster beds of the Dutch Wadden Sea were studied for the period 1999–2013. Cox’s proportional hazard rate model with covariates such as orbital speed, exposure time and bed size and type showed that large, low-lying beds that experience a low orbital speed live longer. Yet the most striking result was that oyster and mixed beds have a much lower hazard rate than pure mussel beds. Simulation studies, using the observed recruitment series, which was very variable, and the estimated survival curves, showed large variability in total bed area, implying that the present area, though lower than before, does not point to a systematic deviation from the pre-1990 situation, that is, the situation before intensive fisheries on these intertidal beds and the disappearance of them around 1990. Claims that bivalve bed recovery is impossible without restoration efforts are premature and not supported by our analysis. On the contrary, the observed high survival rate of mixed and oyster beds and the expectation that such beds will predominate in the near future can easily result in larger future bed coverage than what has been measured before.