The effects of the polychaete Nereis diversicolor on the distribution and transplanting success of Zostera noltii

Loss of saltmarsh vegetation in south-east England is a significant problem for conservation and coastal defence. The losses of vegetation began in th e 1930s with the loss of intertidal Zoster a marina and have continued more recently. Some preliminary trials at reestablishing Zostera in some estuar ies of Essex have not been successful. This paper addresses the hypothesis that the infauna. particularly the polychaete Nereis diversicolor, may rest rict natural colonisation by Zostera and reduce the success of transplantin g trials. In field experiments, Z. noltii were transplanted into areas wher e Nereis were common, close to an established seagrass bed and into two eth er estuaries. The transplants protected from the effects of the polychaetes by netting had a higher survival rate, lower index of root damage and grea ter biomass at the end of the experiments than those that were unprotected. In laboratory experiments, Nereis reduced the survival of Z, noltii. They were observed grasping the leaves and pulling them into their burrows. Thes e results indicate that herbivory and disturbance by N. diversicolor is res ponsible, st least in part, for the restriction of the distribution of Z. n oltii and may have been important in limiting the success of previous trans planting experiments. A hypothesis is proposed which states that there are two stable states on the upper mudflats. One state is dominated by plants, including Zostera spp., which prevent colonisation by burrowing infauna, an d the other is dominated by infauna which prevent colonisation by plants. M anaging these two states could be the key to re-establishing the early succ essional stages of saltmarsh development.