The risk of flood disasters is increasing for many coastal societies owing to global and regional changes in climate conditions, sea-level rise, land subsidence and sediment supply. At the same time, in many locations, conventional coastal engineering solutions such as sea walls are increasingly challenged by these changes and their maintenance may become unsustainable. We argue that flood protection by ecosystem creation and restoration can provide a more sustainable, cost-effective and ecologically sound alternative to conventional coastal engineering and that, in suitable locations, it should be implemented globally and on a large scale.

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Many exploited fish and macroinvertebrates that utilize the coastal zone have declined, and the causes of these declines, apart from overfishing, remain largely unresolved. Degradation of essential habitats has resulted in habitats that are no longer adequate to fulfil nursery, feeding, or reproductive functions, yet the degree to which coastal habitats are important for exploited species has not been quantified. Thus, we reviewed and synthesized literature on the ecological value of coastal habitats (i.e. seagrass beds, shallow subtidal and intertidal habitats, kelp beds, shallow open water habitats, saltmarshes, mussel beds, macroalgal beds, rocky bottom, and mariculture beds) as feeding grounds, nursery areas, spawning areas, and migration routes of 59 taxa, for which the International Council for the Exploration of the Sea (ICES) gives management advice, and another 12 commercially or ecologically important species. In addition, we provide detailed information on coastal habitat use for plaice (Pleuronectes platessa), cod (Gadus morhua), brown shrimp (Crangon crangon), and European lobster (Homarus gammarus). Collectively, 44% of all ICES species utilized coastal habitats, and these stocks contributed 77% of the commercial landings of ICES-advice species, indicating that coastal habitats are critical to population persistence and fishery yield of ICES species. These findings will aid in defining key habitats for protection and restoration and provide baseline information needed to define knowledge gaps for quantifying the habitat value for exploited fish and invertebrates.

We quantified the distribution, abundance, biomass and assemblage structure of benthic macrofauna at different spatio-temporal scales in a temperate estuarine, intertidal soft-sediment environment in the Schelde estuary, The Netherlands. Hierarchically scaled surveys were conducted yearly between 1994 and 2000, covering 4 spatial scales: region (10 4 m), transect (10 3 m), station (10 2 m), and replicate samples (10 -1 m). Our approach provided a powerful framework for quantifying the proportion of the variation among samples that was attributable to each spatial or temporal scale, and we explicitly aimed at identifying the role of environmental variables in explaining the observed variability. Variance components calculated for 11 dominant macrobenthic species revealed that variations at the scale of stations and year × station interactions were the most important components of variability. Regional and transect differences were only apparent for a few species, although multivariate analysis revealed clear inter-regional differences for the macrobenthic assemblage structure. Only a few species displayed significant variability associated with the factor year solely. Both spatial and temporal components explained > 70% of the total variance. A substantial part of the total variation in abundance of individual species was explained by the observed environmental variables (27 to 56%). Multiple regression with subdivision of the environmental variables into a long-term average and a temporal component showed that the long-term averages were much more important than the short-term deviations from this average, with local environmental variables (mud content, chlorophyll a, bed level height) explaining the largest part of the observed variation. For a few species and total biomass, salinity also explained a large part of the observed variation. Canonical correspondence analysis (CCA) with forward selection revealed that salinity and mud content, and to a lesser extent chlorophyll a and bed-level height, accounted for most of the variance in the macrobenthic species data. Partial CCA indicated that of the variation in the species data a large part was spatially structured (56.7%), with about half of this variation being explained by the environmental variables used. Only 4.1% of the species variation was temporally structured. Our results have important consequences for both the interpretation of monitoring programmes and the enhancement of sampling designs.

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Estuaries are naturally highly dynamic and rapidly changing systems, forming a complex mixture of many different habitat types. They are very productive biomes and support many important ecosystem functions: biogeochemical cycling and movement of nutrients, mitigation of floods, maintenance of biodiversity and biological production. Human pressure on estuaries is very high. On the other hand, it is recognized that estuaries have a unique functional and structural biodiversity. Therefore, these ecosystems are particularly important for integrating sound ecological management with sustainable economics. These opportunities are explored for the Scheldt estuary, a well-documented system with an exceptional tidal freshwater area. In this article a description of the Scheldt estuary is presented, illustrating that human influence is intertwined with natural dynamics. Hydrology, geomorphology, trophic status and diversity are discussed, and possible future trends in both natural evolution and management are argued.

Coastal sediments in sheltered temperate locations are strongly modiWed by ecosystem engineering species such as marsh plants, seagrass, and algae as well as by epibenthic and endobenthic invertebrates. These ecosystem engineers are shaping the coastal sea and landscape, control particulate and dissolved material Xuxes between the land and sea, and between the benthos and the passing water or air. Above all, habitat engineering exerts facilitating and inhibiting eVects on biodiversity. Despite a strongly growing interest in the functional role of ecosystem engineering over the recent years, compared to food web analyses, the conceptual understanding of engineering-mediated species interactions is still in its infancy. In the present paper, we provide a concise overview on current insights and propose two hypotheses on the general mechanisms by which ecosystem engineering may aVect biodiversity in coastal sediments. We hypothesise that autogenic and allogenic ecosystem engineers have inverse eVects on epibenthic and endobenthic biodiversity in coastal sediments. The primarily autogenic structures of the epibenthos achieve high diversity at the expense of endobenthos, whilst allogenic sediment reworking by infauna may facilitate other infauna and inhibits epibenthos. On a larger scale, these antagonistic processes generate patchiness and habitat diversity. Due to such interaction, anthropogenic inXuences can strongly modify the engineering community by removing autogenic ecosystem engineers through coastal engineering or bottom trawling. Another source of anthropogenic inXuences comes from introducing invasive engineers, from which the impact is often hard to predict. We hypothesise that the local biodiversity eVects of invasive ecosystem engineers will depend on the engineering strength of the invasive species, with engineering strength deWned as the number of habitats it can invade and the extent of modiWcation. At a larger scale of an entire shore, biodiversity need not be decreased by invasive engineers and may even increase. On a global scale, invasive engineers may cause shore biota to converge, especially visually due to the presence of epibenthic structures.