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Analysis of biological traits within assemblages is increasingly used as a proxy for ecological functioning. However, taxa often show plasticity in the expression of traits and can potentially change trait expression depending on local conditions. While many forms of disturbance will lead to changes in the species composition of the assemblage, small-scale disturbances can trigger alterations in the behaviour of taxa and hence the ecological roles they are delivering. Such changes would not be detected by biological traits analysis (BTA) alone. BTA therefore has the potential to misinform as to the contribution of assemblages to ecological processes. To assess the potential for taxa to change their expression of traits, the feeding modes of 8 taxa from 2 intertidal assemblages in north-west England, UK, were investigated using stable isotope analyses following experimental sediment disturbance and removal of cocklesCerastoderma edule. Two of the 8 taxa exhibited significant changes to their isotopic composition within disturbed plots. Short-term plastic changes to food web dynamics following changes in environmental conditions have implications for the suitability of BTA as a tool for investigating ecosystem function. Although BTA provides much insight into the ecological roles of taxa within systems and can be extremely effective at identifying changes associated with different assemblage compositions, it is conceivable that changes to ecological functioning may be undetected by BTA alone, and hence there is the need for this approach to be supported by experimental observation.

The organisms living on and in the sea floor, the benthos, represent an important ecological group. Although some (shellfish) have an economic value, most do not, and so little long-term data are available. We have identified three sources of historic benthic data for the North Sea, a regional sea that has been subjected to multiple human impacts for at least several hundred years. Each dataset has its limitations, but by their use together some issues emerge. Wider community shifts were observed in the shorter term and a number of extirpations at the scale of the North Sea were seen over longer time scales. The extirpated taxa share a number of characteristics consistent with an effect of fisheries such as fragile morphology. We must concentrate now on furthering our understanding of the ecological significance of shifts in dominance of particular functional units and protecting those habitats and species most vulnerable to fisheries-driven extirpation.

1. Aquatic invasive species are a growing concern to environmental managers because of their diverse impacts on aquatic biodiversity and high eradication costs, necessitating effective management policies. In this study, we evaluate the ability of environmental and socioeconomic factors to predict the risk of invasion in Great Britain and Ireland of 12 potential aquatic invaders covering all major aquatic groups. Despite their potential to inform risk assessments, this is the first time socio-economic factors related to propagule pressure have been specifically integrated in distribution modelling. 2. Species distribution models (SDM, MaxEnt algorithm) were calibrated with a set of environmental factors (e.g. bioclimatic, geographical and geological) and integrated with socioeconomic (e.g. human influence index, population density, closeness to ports) predictors. 3. The inclusion of socio-economic factors in SDM did not affect accuracy scores (AUC already >0·90), but their effects were more pronounced in spatial predictions, resulting in up to a sixfold amplification of the area predicted suitable for each species. Despite the inclusion of potential surrogates of water chemistry (e.g. geology) and propagule pressure (e.g. population density), temperature-related variables were most important predictors of aquatic species' distributions. 4. According to SDM, the environmental suitability for a suite of invaders belonging to different taxonomic groups and regions of origin is greatest in east and south-east England and decreases towards the north and west. Multiple invasions in this region are of special concern, as species are known to modify their habitat facilitating subsequent invasions, thereby potentially exacerbating their impacts. 5. Major management regions to be prioritized in monitoring programmes include the Humber, Thames and Anglian River Basin Districts. Species of special concern include a mysid (Hemimysis anomala), a gammarid (Dikerogammarus villosus), a plant (Ludwigia grandiflora) and two crayfishes (Procambarus clarkii and P. fallax). 6. Synthesis and Applications. The inclusion of socio-economic factors in species distribution models has the potential to improve predictions of areas under a highest risk of multiple invasions and to help disentangle the complex interplay between biological invasions and global environmental and socio-economic processes. Such understanding is pivotal to prioritize limited resources for the optimum prevention and control of biological invasions.

Ecosystem functioning underpins the ecosystem services upon which humans rely. Critical functions, such as primary and secondary productivity, are, however, increasingly threatened by a range of anthropogenic stressors. Although the extent of the threat of contamination is large and has been increasing, pollution is one of the least‐studied stressors in ecology. We did a systematic review and critical synthesis of the effects of contaminants on marine and estuarine ecosystem functioning. No other stressors besides toxic chemicals were included in this review. We identified 264 relevant studies across a range of contaminants. Toxic contaminants generally altered marine ecosystem functioning by reducing productivity and increasing respiration. Effects varied, however, according to the type of contaminant and the component(s) of the system studied (e.g. particular trophic levels, functional groups or taxonomic groups). Toxicity studies that included a measure of ecosystem function were strongly biased towards planktonic communities in contrast to studies of biodiversity, which have been dominated by work on soft‐sediment communities. Toxicant studies that included measures of ecosystem function rarely included a measure of biodiversity and rarely interpreted their findings within an ecosystem function context. Studies that included multiple components of an ecosystem, that is more than one functional group of organisms, were more likely to find no effect of contamination, possibly due to ecological interactions. Studies that suffered from unclear or flawed methodology were more likely to find a significant impact of contaminants on some endpoints of ecosystem functioning than studies with appropriate designs. Synthesis and applications. Up to 70% of studies found negative impacts of contaminants on primary production. Toxic contaminants therefore have the potential to greatly affect the ecosystem services and benefits provided by these systems. Our findings will help managers and policymakers to determine whether contaminants are affecting both biodiversity and ecosystem functioning in a given context, therefore helping to prioritize areas for remediation. There is still, however, much to understand about the relationships between biological diversity and ecosystem functioning. Our understanding of chemical contaminant effects will remain patchy until direct measures of both variables are undertaken within multiple ecosystems. We therefore recommend the adoption of functional endpoints, such as productivity and respiration, in ecological studies, routine toxicological studies and ecological risk assessment.

Global freshwater demand is increasing dramatically, with water withdrawal rates more than tripling in the last five decades. Consequently, alteration of water level regimes, particularly in the form of amplified water level fluctuations (WLF), is rapidly becoming one of the major disturbances of aquatic ecosystems globally. However, even though the impacts of WLF are likely to be strongest in littoral zones, little is known about their effects on the structure and functioning of littoral assemblages in standing water systems. We established an experiment in large outdoor pond mesocosms to examine the effects of WLF on littoral assemblages and explore the potential for development of ecological indicators of WLF. Water level fluctuations reduced benthic algal biomass and the density and taxonomic distinctness of benthic invertebrate assemblages. Both the taxonomic and trophic structure of benthic assemblages were altered significantly in ponds with WLF and homogenized along the depth gradient. Synthesis and applications. Our results indicate that water level fluctuations (WLF) can reduce considerably the productivity and biological diversity of lake littoral zones. Given that the problem is likely to be exacerbated by predicted increases in climatic variability and enhanced demand for water and hydropower, our findings have important implications for the conservation and management of global aquatic biodiversity. We identified several specific ways that WLF modify littoral assemblages along the depth gradient. This ability to identify separate pressures is an important requirement of robust ecological assessment tools. This study confers potential for development of ecological indicators of WLF in standing waters, provides indication of sampling strategies to be employed and demonstrates the need to mitigate the most extreme water withdrawals.

Early detection is invaluable for the cost‐effective control and eradication of invasive species, yet many traditional sampling techniques are ineffective at the low population abundances found at the onset of the invasion process. Environmental DNA (eDNA) is a promising and sensitive tool for early detection of some invasive species, but its efficacy has not yet been evaluated for many taxonomic groups and habitat types. We evaluated the ability of eDNA to detect the invasive rusty crayfish Orconectes rusticus and to reflect patterns of its relative abundance, in upper Midwest, USA, inland lakes. We paired conventional baited trapping as a measure of crayfish relative abundance with water samples for eDNA, which were analysed in the laboratory with a qPCR assay. We modelled detection probability for O. rusticus eDNA using relative abundance and site characteristics as covariates and also tested the relationship between eDNA copy number and O. rusticus relative abundance. We detected O. rusticus eDNA in all lakes where this species was collected by trapping, down to low relative abundances, as well as in two lakes where trap catch was zero. Detection probability of O. rusticus eDNA was well predicted by relative abundance of this species and lake water clarity. However, there was poor correspondence between eDNA copy number and O. rusticus relative abundance estimated by trap catches. Synthesis and applications. Our study demonstrates a field and laboratory protocol for eDNA monitoring of crayfish invasions, with results of statistical models that provide guidance of sampling effort and detection probabilities for researchers in other regions and systems. We propose eDNA be included as a tool in surveillance for invasive or imperilled crayfishes and other benthic arthropods.

1. Like many ecosystem functions in marine and terrestrial environments, nutrient processing varies dramatically over small spatial scales, making efforts to apply findings within and across ecosystems challenging. In estuaries, information on the influence of habitat context on sediment nutrient cycling is lacking even though this is an important estuarine function with high societal value. 2. We collected triplicate intact sediment cores from restored oyster reefs located in different habitat contexts (adjacent to salt marshes, seagrass beds and mudflats), as well as salt marshes, seagrass beds and mudflats without reefs (controls). Sediment denitrification and fluxes of dissolved inorganic nitrogen were measured under ambient and experimentally elevated water column nitrate levels. 3. Under ambient nitrate, oyster reefs enhanced sediment denitrification by 18-275% over the controls, with highest rates of denitrification in the mudflat context. With experimentally elevated nitrate, the rate of denitrification was higher for oyster reefs compared to the controls in all contexts. This suggests that oyster reefs prime sediments to denitrify nitrate pulses by providing a labile carbon source for denitrifying bacteria. 4. There was a weak positive relationship between oyster density and denitrification under ambient nitrate concentrations and a positive relationship with denitrification that became negative beyond ~ 2400 individuals m⁻² with elevated nitrate concentrations. The effect of the oyster reef on sediment denitrification was most pronounced in the mudflat context, due to the absence of other structured habitats and higher oyster density, compared to the other two habitat contexts investigated. 5. The consistency of denitrification efficiency across the habitats and lack of difference between habitats with reefs and those without (controls) suggest oyster-mediated denitrification is an effective sink for nitrogen in coastal systems. 6. Synthesis and applications. Our study indicates that oyster-mediated denitrification is dependent on the habitat context of the oyster reef, and variation in oyster density and the relative functional redundancy of oyster reefs where other structured habitats exist (e.g. seagrass and salt marshes) may explain this pattern. Efforts to model and predict ecosystem services provided through oyster reef restoration such as the removal of anthropogenically derived nitrogen should incorporate how habitat context influences ecosystem functions.