Changes in the sublittoral faunal biomass induced by the discharge of a polluted river along the adjacent rocky coast (N. Spain)

Abstract

Sublittoral hard bottom assemblages in the 'Abra de Bilbao' bay (N. Spain) were described in terms of biomass in order to record spatial changes on scales of a few km that reflect they prevalence of perturbation gradients. Several criteria and levels of data aggregation were proposed and tested in an attempt to obtain information on the degree of redundancy achieved by such communities for further monitoring programmes. The area of study is at present recovering from a highly stressed situation of turbidity and sedimentation. In this way, the fauna/flora biomass ratio (A/V) proved to be a useful descriptor indicative of several environmental conditions from healthy to grossly perturbed on rocky communities. In addition, the high degree of redundancy shown by the macrozoobenthos allows efforts to be concentrated on only the faunal component, using different approaches and data aggregation levels. As a result, the cost-effectiveness of monitoring programmes could increase considerably. Moreover, the use of several techniques (univariate, multivariate) and approaches (taxonomic, trophic, mixed) is recommended for the monitoring of hard bottom communities, in order to test the robustness of the results obtained and achieve other complementary perspectives upon the biota with the same data sets. In this case study, relevant information was acquired on the possible temporal changes of intermediate zones of the 'Abra de Bilbao' due to the biological recovery of the area. Therefore, an adequate combination of biomass values and the concepts of redundancy-sufficiency is suggested as a realistic way of developing future monitoring programmes for rocky shores in other areas.