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

Abstract

Loss of saltmarsh vegetation in south-east England is a significant problem for conservation and coastal defence. The losses of vegetation began in the 1930s with the loss of intertidal Zostera marina and have continued more recently. Some preliminary trials at reestablishing Zostera in some estuaries of Essex have not been successful. This paper addresses the hypothesis that the infauna, particularly the polychaete Nereis diversicolor, may restrict natural colonisation by Zostera and reduce the success of transplanting trials. In field experiments, Z. noltii were transplanted into areas where Nereis were common, close to an established seagrass bed and into two other estuaries. The transplants protected from the effects of the polychaetes by netting had a higher survival rate, lower index of root damage and greater 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. These results indicate that herbivory and disturbance by N. diversicolor is responsible, at least in part, for the restriction of the distribution of Z. noltii and may have been important in limiting the success of previous transplanting 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, and the other is dominated by infauna which prevent colonisation by plants. Managing these two states could be the key to re-establishing the early successional stages of saltmarsh development.

Suppressing antagonistic bioengineering feedbacks doubles restoration success

“…Surprisingly, however, these papers neglect the potential restoration benefits of the removal of negative interactions originating from ecosystem engineers, despite the fact that such interactions can play an important role in marine habitats (Rhoads and Young 1970, Philippart 1994, Hughes et al 2000, Hughes and Paramor 2004, Siebert and Branch 2006, Berkenbusch et al 2007, van Wesenbeeck et al 2007. In this study, we show that suppressing such negative ecosystem-engineering effects could be a useful approach in restoration and conservation efforts by giving at least a better start during the initial establishment phase.…”

“…For example, this has been shown for the negative effect of deposit feeders on filter feeders by making sediment more erosive, causing filter feeding to be hampered by more turbid water (i.e., trophic group amensalism; Rhoads and Young 1970). Several studies have also demonstrated that negative interactions between benthos and vegetation can be very strong (Philippart 1994, Hughes et al 2000, Hughes and Paramor 2004, Siebert and Branch 2006, Berkenbusch et al 2007, van Wesenbeeck et al 2007). For instance, ''biomechanical warfare'' between ecosystem-engineering salt marsh vegetation and infauna can cause a bimodal species distribution on the salt marsh-mudflat interface, as bioturbation prevented plant colonization in the invertebrate-dominated state and invertebrates were excluded by sediment compaction in the plantdominated state (van Wesenbeeck et al 2007).…”

The importance of reproductive strategies in population genetic approaches to conservation: an example from the marine angiosperm genus Zostera

“…Hootsmans et al (1987) observed maximum recruitment at 10 psu and no recruitment above 30 psu in natural populations. Likewise, under experimental conditions, the highest levels of germination were observed at salinity levels of between 1 and 10 psu with no germination above 20 psu (Hughes et al 2000).…”

Effects of the invertebrate infauna on early saltmarsh plant colonisation of managed realignment areas in south-east England

“…Paramor & Hughes (2004) presented evidence that loss of saltmarsh vegetation from the pioneer zone, and by internal erosion of saltmarsh creeks, was exacerbated by bioturbation and herbivory by the infauna, particularly the ragworm Nereis diversicolor. N. diversicolor may occur high in the intertidal zone where they are predominantly surface deposit-feeders and consume microphytobenthos (Smith et al 1997), filamentous algae (Hughes 1999) and the seeds and seedlings of saltmarsh plants (Hughes et al 2000, Paramor & Hughes 2004. Bioturbation by the amphipod Corophium volutator may also destabilise the sediment and prevent establishment of seedlings of saltmarsh plants (Gerdol & Hughes 1993).…”