Summary1. The saltmarshes of south-east England are eroding rapidly. Field and laboratory experiments were used to test the hypotheses that: (i) at the mudflat-saltmarsh boundary there are two alternative states, one dominated by pioneer zone vegetation that excludes burrowing infauna, and the other dominated by infaunal invertebrates that exclude vegetation; and (ii) the major cause of the loss of saltmarshes in south-east England is internal creek erosion, which is exacerbated by bioturbation and herbivory by the infaunal polychaete Nereis diversicolor . 2.In laboratory experiments Nereis ate the seeds and seedlings of Salicornia spp., and Salicornia deterred burrowing by Nereis . In field experiments, at Tollesbury in Essex, UK, exclusion of Nereis from the sediment surface increased the density of Salicornia , but only when a source of seeds was close by. In the Tollesbury saltmarsh the plants and Nereis had mutually exclusive distributions within a vertical zone of overlap. The recently vegetated area of the managed realignment site at Tollesbury contained no Nereis , but Nereis colonized areas where Salicornia had been removed. These observations and data support the first hypothesis. 3. Much of the loss of the Tollesbury saltmarsh is by lateral erosion of the internal creeks. Physical factors alone cannot be responsible for this erosion because experimental exclusion of Nereis led to sediment accretion. These results support the second hypothesis. Creek erosion may create a positive feedback where creek enlargement leads to faster tidal currents and further erosion until creeks have widened to their new equilibrium morphology. 4. Synthesis and applications . We conclude that the infauna are a major cause of reduction in area of saltmarsh vegetation and this has implications for the management of saltmarsh restoration. These results call into question the assumption that saltmarsh erosion in south-east England is due to sea level rise and coastal squeeze, and demands reexamination of the role of management realignment in the regeneration of saltmarshes. Reducing the rates of saltmarsh creek erosion, by exclusion of the infauna, and/or by reducing current velocities in the saltmarsh creeks, would reduce the need to replace eroded marshes by managed realignment, and would reduce future erosion of existing sea walls by wave action.

Summary1. The saltmarshes of south-east England have been eroding rapidly for about the last 50 years, at a continuing rate of about 40 ha year − 1 , with deleterious consequences for conservation and coastal flood defence. The possible reasons for this erosion and suitability of methods of saltmarsh restoration are discussed. 2. The prevailing hypothesis that the saltmarsh erosion is due to coastal squeeze, where sea walls prevent a landward migration of saltmarsh in response to sea level rise, is rejected because: (i) as the sea level rises saltmarshes accrete vertically as well, at least at the same rate, and may even extend seaward; (ii) in recent decades the rate of rise in sea level has been no higher than in the past when the saltmarshes developed; (iii) the pattern of vegetation loss, mostly of pioneer zone species, is opposite to that predicted by coastal squeeze, where the upper marsh plants should disappear first. 3. Alternative explanations and hypotheses are proposed that relate the recent saltmarsh erosion to changes to the intertidal biota, an increase in abundance of the infaunal polychaete Nereis diversicolor , and a decrease in abundance of intertidal seagrasses. Bioturbation and herbivory by Nereis cause the loss of pioneer zone plants, increase sediment instability and exacerbate the erosion of saltmarsh creeks. The erosion of the seaward edge of some marshes may also be due to increased wave action, and increased tidal current speeds in estuaries, following the loss of intertidal seagrasses since the 1930s through wasting disease. 4. Synthesis and applications. The current strategy for saltmarsh creation is based on managed realignment, where some sea walls are breached to provide new intertidal habitat. The conclusion that the causes of saltmarsh loss are not related to sea level rise calls into question this dependence on management realignment as the most appropriate means of saltmarsh creation, not least because many realignment areas are unlikely to develop vegetation. Other methods should be considered for creating new marshes and for reducing/reversing marsh erosion. These include, alone or in combinations, exclusion of the infauna, use of dredged material for strategic intertidal recharge, and transplantation of intertidal seagrasses.

Many studies have examined the effects of surface topography on the settlement behaviour of marine organisms and this article reviews these investigations with more emphasis on the effects of topography scale. It has been observed that macro topographies (1-100 mm) are generally favoured by marine fouling taxa and are unsuitable for antifouling applications. This is because macro topographies are usually large enough to fit fouling organisms and provide refuge from dangers in the marine environment. Micro topographies had only limited success at reducing fouling from a wide range of marine taxa. The antifouling performance of micro topographies (1 to ≤ 1000 μm) is dependent on the properties of topography features in terms of symmetry, isotropy, width, length, height/depth, separation distance and average roughness. In terms of the antifouling performance of micro topography, topography geometry may only be of secondary importance in comparison to the size of features itself. It is also noted that hydrodynamic stresses also contribute to the settlement trends of foulers on textured surfaces. Future studies on antifouling topographies should be directed to hierarchical topographies because the mixed topography scales might potentially reduce fouling by both micro and macro organisms. Patterned nano-topographies (1- ≤ 1000 nm) should also be explored because the antifouling mechanisms of these topographies are not yet clear.

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Marine protected areas are generally designed and managed on the basis of the presence and extent of specific habitat types or the habitats of important species. However, it has become clear that in addition to including these 'structural' elements of marine systems, management strategies should incorporate a consideration of the functional aspects of the ecosystems. Biological traits analysis (BTA) has been successfully used to describe ecological functioning in marine benthic systems. BTA uses a number of biological characteristics expressed by the taxa present as indicators of key ecosystem functions. Two expert workshops were used to examine the potential for the application of BTA in the designation and management of MPAs. They concluded that BTA represented the best tool currently available for quantifying ecological functioning and agreed on 10-key ecological functions delivered by marine benthic communities. Twenty-four biological traits were also identified by the workshops as indices of these ten functions. In order to demonstrate the practical utility of the approach, BTA using these traits, was applied to a dataset covering benthos from within and around the proposed Eddystone Special Area of Conservation (SW England). The case study demonstrated that with the type of data normally available from conservation assessment type surveys, and a knowledge of the relevant biological traits, it is possible to use a consideration of ecological functioning to set boundaries for the MPA and to inform the site management objectives. The use of structure and function information to inform the designation process and subsequent management of marine protected areas is discussed

In the Welsh part of the Irish Sea, a method was developed for assessing the sensitivity of different seabed habitats to existing fishing activities, across a range of potential fishing intensities. The resistance of 31 habitats and their associated biological assemblage to damage by 14 categories of fishing activity were assessed along with the rate at which each habitat would recover following impact (resilience). Sensitivity was scored based on a combination of the resistance of a habitat to damage and its subsequent rate of recovery. The assessments were based, wherever possible, on scientific literature, with expert judgement used to extrapolate results to habitat and gear combinations not directly examined in the published literature. The resulting sensitivity matrices were then subject to further peer review at a series of workshops. Following consensus on the habitat sensitivity, these data were combined with the most resolved sea-floor habitat maps. These habitat sensitivity maps can help inform the development of site-specific management plans, as well as having a place in spatial planning and aiding managers in developing dialogue with other stakeholders. A case study of their application is provided.

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.

A critical review of microplastic pollution in urban freshwater environments and legislative progress in China: recommendations and insightsFreshwater systems are vitally important, supporting diversity and providing a range of ecosystem services. In China, rapid urbanization (over 800 million urban population) has led to multiple anthropogenic pressures that threaten urban freshwater environments.Microplastics (<5 mm) result from intensive production and use of plastic materials, but their effects in urban freshwater environments remain poorly understood. Rising concerns over the ecological effects of microplastics have resulted in increased attention being given to this contaminant in Chinese freshwater systems. Some studies provide quantitative data on contamination loads, but in general relevant knowledge in freshwater environment remains narrow in China, and lacking adequate understanding of threshold levels for detrimental effects. Notably, non-standardized sample collection and processing techniques for point and non-point sources have hindered comparisons of contamination loads and associated risk. Meanwhile, legislative frameworks for managing microplastics in China remain in their infancy. This manuscript critically reviews what is known of the nature and magnitude of microplastic pollution in Chinese freshwater environments, and summarises relevant Chinese legislation. It provides recommendations for improving the legislative framework in China and identifies research gaps that need to be addressed to improve management and regulatory strategies for dealing with microplastic pollution in Chinese urban freshwater environments.