Realistic assessments of the ecological status of benthic habitats, as requested by European directives such as the Water Framework Directive and the European Marine Strategy Framework Directive, require biotic indices capable of detecting anthropogenic impact without having preliminary knowledge of the occurring pressures. In this context, a new general-purpose biotic index (GPBI) based on the deviation of benthic macrofauna community composition and structure from a valid reference (i.e., good ecological status) is proposed. GPBI is based on the assumption that as a site becomes impacted by a pressure, the most sensitive species are the first to disappear, and that stronger impacts lead to more important losses. Thus, it explicitly uses the within-species loss of individuals in the tested station in comparison to one or several reference stations as the basis of ecological status assessment. In this study, GPBI is successfully used in four case studies considering the impact of diversified pressures on benthic fauna: (1) maerl extraction in the northern Bay of Biscay, (2–3) dredging and trawling in the North Sea, and (4) hypoxic events at the seafloor in the Gullmarfjord. Our results show that GPBI was able to efficiently detect the impact of the different physical disturbances as well as that of hypoxia and that it performs better than commonly used pressure-specific indices (M-AMBI and TDI). Signal detection theory was used to propose a sound good/moderate ecological quality status boundary, and recommendations for future monitoring are also provided based on the reported performance of GPBI.

The sustainability of mangrove ecosystems requires a knowledge of their spatiotemporal variability as a function of regional properties. The unique coastal ecosystems of the mangrove belt along the coast of the Guianas in South America are influenced by cycles of a massive accretion of mud supplied by the Amazon River and wave induced erosion. This study characterized, for the first time, how benthic infaunal assemblages, as proxies of mechanisms of mangrove resilience, were structured by the natural growth track of Avicennia germinans dominated mangroves in French Guiana. We sampled 4 mobile mud stations and 27 consolidated mud stations distributed over 9 tidal transects from bare to vegetated mudflats colonized by young mangroves during the dry season. We collected a complete dataset of sediment and vegetation variables together with the benthic meso- (>0.25 mm) and macrofauna (>1 mm). We used a combination of eigenvector based multivariate analyses and variance partitioning on this multiple set of variables to identify which environmental variables likely drive the benthic diversity patterns. Mangrove early development increased the alpha and beta diversities of the infaunal communities for the two size classes. A total of 20–30% and 7–12% of the beta diversity are explained by linear and nonlinear spatial variables, respectively. However, 7% to 9% of the variance partioning could be determined by other biotic/abiotic variables, biological interactions or neutral processes, not described here. This study has highlighted the necessity of taking into account mangrove dynamics at suitable spatial scales for benthic biodiversity evaluation and mangrove management or restoration plans.