MEPS 303:61-71 (2005)  -  doi:10.3354/meps303061

ABSTRACT: Saltmarsh erosion on the subsiding coastline of SE England is a major conservation problem and necessitates increased expenditure on maintaining sea walls. The preferred management solution is selective managed realignment (set-back), where sea walls are breached to allow new intertidal land to develop into saltmarsh. We tested the hypothesis that saltmarsh would not necessarily develop in low-lying realignment sites on subsiding coasts, because the accreting sediment would be colonised first by infaunal invertebrates, particularly the polychaete Nereis diversicolor, which would prevent development of vegetation through bioturbation and herbivory. The hypothesis was supported by data on the distributions of the plants and invertebrates in the experimental managed realignment sites at Tollesbury and Orplands, and from infauna exclusion experiments. Tollesbury mostly developed into mudflat colonised mainly by N. diversicolor and Hydrobia ulvae, with only a narrow zone of saltmarsh vegetation in the highest area where little sediment had accreted. In contrast, most of the Orplands site was relatively high and, apart from some low-lying basins, little sediment accretion occurred and the area was soon largely covered with saltmarsh vegetation. In experimental N. diversicolor exclusion areas, the abundance of microphytobenthos and filamentous algae and sediment accretion increased at both sites, but saltmarsh vegetation only developed at Orplands, probably because the seeds at Tollesbury were buried by rapidly accreting sediment. Further management of low-lying realignment areas is necessary to prevent invertebrate colonisation and help promote saltmarsh development. The experiments also indicate that marsh regeneration need not depend on realignment and should be possible on existing mudflats.

KEY WORDS: Managed realignment · Saltmarsh restoration · Nereis diversicolor