Ecological assessment of soft bottom benthic communities in northern Spanish estuaries

Abstract

Abstract The implementation of the Water Framework Directive requires the classification of the ecological quality status of benthic macroinvertebrates in costal and transitional waters. The uncertainty and complexity of this task have lead to the creation of specific Geographical Intercalibration Groups (GIGs) for the different ecoregions and types of water bodies established. In this framework, several metrics are under study in the United Kingdom, Spain and Denmark for North East Atlantic coastal waters (NEA-GIG). All of them include in their formulations the AMBI index. Nevertheless, few advances have been made in relation to transitional waters. This paper aims to test the suitability of those methodological procedures for their application in Northern Spanish estuaries. The results show evident divergences in classification of ecological status among methods, although the correlations of corresponding ecological quality ratios (EQRs) are good. Thus, we think that it may be necessary to modify the boundaries between each ecological status category and adjust the reference conditions for the variety of community-types existing in estuarine water bodies. However, some problems arise in the assessment of some naturally stressed communities. In this situation, we found an overall dominance of species tolerant to organic enrichment in all status categories and low range of variation of AMBI index. This aspect introduces some uncertainty in relation to the ability of this index to detect a deleterious effect in these estuarine communities naturally stressed. On the other hand, we found some sites that achieve good status according to the metrics used, even though the number of opportunistic species was high. The use of combined approaches that incorporate physicochemical condition of sediments would be a straightforward approach to reduce the risk of failing in the assignation of ecological status category.