Population dynamics of subtidal blue mussels Mytilus edulis and the impact of cultivation

Jj Capelle,Ac Smaal,Mr Van Stralen,Jwm Wijsman,Pmj Herman

doi:10.3354/aei00221

Abstract

Fishery on subtidal mussel beds and subsequent relying on culture plots in the same system is a common practice in bottom mussel culture. We address factors that determine the population dynamics of subtidal blue mussels Mytilus edulis L. and to what extent total (natural plus cultured) subtidal mussel biomass in the system is affected by fishery practices. Mussel size and density of spatially segregated natural and cultured subtidal mussel populations in the western Wadden Sea were measured over time in 2 field studies. Spatial patterns in survival rates showed better spat survival in areas with lower salinity and lower density of sea stars Asterias rubens. This suggests that mussel survival is negatively related to sea star distribution which is to a large extent controlled by salinity. The Asterias−Mytilus relation in the Wadden Sea is an example of the concept that environmental stress determines the successes of the prey by affecting the prey− predator relationship. Natural beds that escape predation are found at lower salinities, and mussels on these beds showed low growth rates, also because of lower food quality in these areas. Mussel culture is strongly affecting the population dynamics of the subtidal mussel population, through relay of mussels from natural mussel beds to culture plots. This activity increases mussel growth and survival, because food quality on culture plots is high and predation is controlled. Despite harvesting, mussel biomass production on culture plots was higher than on natural mussel beds, enhancing total subtidal mussel stock.

Highlights

Bottom culture of mussels is an extensive largescale form of aquaculture that is practiced in shallow subtidal and intertidal sand/mud flats in coastal areas (Gosling 2003)
We address which factors determine the population dynamics of subtidal blue mussel Mytilus edulis and to what extent the total subtidal mussel biomass in the system is affected by fishery practices, such as mussel seed dredging, relaying and subsequent harvesting
The likelihood ratio test between von Bertalanffy growth function (VBGF) with separate versus common parameters for mussel growth provides evidence that VBGF parameters differ between mussels on natural beds and mussels on culture plots

Summary

Introduction

Bottom culture of mussels is an extensive largescale form of aquaculture that is practiced in shallow subtidal and intertidal sand/mud flats in coastal areas (Gosling 2003). The shallow sand/mudflats are habitats for ecologically important habitat-creating communities (e.g. mussels, sea grasses, oysters, Sabellaria) and vital foraging areas for birds and fishes (Lenihan & Micheli 2001, Van de Kam et al 2004). These ecological values may be impacted by culture activities, which include the translocation of juvenile mussels from natural beds (mussel seed) to culture plots. Effects of mussel seed fishery on benthic biodiversity, habitat structure and natural

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