Cystoseira baccata, a biological quality element for the implementation of the Water Framework and Marine Strategy EU Directives, is a dominant species in the subtidal rocky bottoms of the Basque coast. As part of this issue and given the need to better understand the functional character of benthic rocky ecosystems and use them as a reference to anthropogenic changes, two samplings campaigns were conducted in 2014 and 2017. Several population parameters (i.e. frond density, frond length frondlength/total frond-length ratio and taxonomic richness of epibionts) of C. baccata were studied from three sites monitored within the Water Directive Framework in relation to bathymetry during the two campaigns. The results showed a significant influence of bathymetry on frond density, frond length and the epibiotic load, and also an effect of sampling time for the seaweed and epibionts (epiflora and epifauna). The characterization of these functional population parameters for C. baccata under natural conditions are extremely valuable for its application to monitoring programs evaluating the ecological status of coastal waters in this region. Highlights ► Contribution of new knowledge on C. baccata habitat and population. ► Confirmation of interest of this engineering species in implementation MSFD. ► Swell effect influencing density and individual height. ► Ratio of length is pertinent metric to discriminate epibiosis considering levels.
Rocky intertidal habitats are particularly vulnerable to anthropogenic pressures especially in areas with high urban concentrations such as southeastern Bay of Biscay. This research aims to establish an assessment of the potential impact of sewage discharges on intertidal rocky benthic assemblages on macroalgae and on macrofauna as required by the European Directives (Water Framework Directive-WFD and Marine Strategy Framework Directive-MSFD). The assemblages were sampled at five locations according to a control-impact design. A moderate detectable effect of discharges was highlighted on the assemblage structure by means of multivariate analyses but this was less evident using other biological and ecological metrics. Results would also suggest that benthic macroalgae constitute for the study area the best relevant biotic component to assess the effect of this pressure on the intertidal rocky platform habitats. Changes in the relative abundance of Ceramium spp., Corallina spp. and Halopteris scoparia were mainly responsible of the dissimilarities found. Finally, a pseudo-ecological quality ratio, based on the current WFD metrics, was also calculated for each site within locations (i.e. each distance from the outfall) to assess its sensitivity to this type of pressure. Results were conformed with those of the WFD monitoring because un-or less-impacted sites were ranked as "Good" contrary to the others ranked as "Moderate". Thus, this work provides additional information for the MSFD and bridges deficiencies emphasized by Directives on the response of biological indicators to various pressures and the biocenosis of southeastern Bay of Biscay. Highlights ► Detectable effects of discharges were highlighted on assemblage structure. ► Macroalgae constituted a relevant biotic component to study impact of WWTP discharges. ► 24 contributors responsible for differences (impacted vs. control) were identified. ► The pseudo-EQR ratio was sensitive to the WWTP pressure.
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