Changes in the sublittoral benthic marine macroalgae in the polluted area of Abra de Bilbao and proximal coast (Northern Spain)

Abstract

Sublittoral communities of macroalgae from the Abra de Bilbao and its surrounding area, which are affected by pollution, were studied in 1984 and 1992. Statistical cluster analysis applied to a network of 230 quadrats distributed along 7 transects resulted in 4 structurtal levels of community, depending on the pollution gradient. These levels are defined by algal cover, vertical layering and the predominant morphology of the species forming the community. Sedimentation, turbidity and water toxicity are the principal destabilizing factors among the phytobenthic communities. Species with simple morphology, mainly ceramiaceous algae (Ceramium diaphanum, Callithamnion neglectum, Antithamnionella spirographidis, Pterothamnion plumula, Anotrichium furcellatum, Compsothamnion thuyoides), sciaphilous (Mesophyllum lichenoides, Zanardinia prototypus, Rhodymenia coespitosella, Drachiella minuta, Erythroglossum laciniatum, Hypoglossum hypoglossoides) and those resistant to sedimentation (Pterosiphonia pennata and Champia parvula) are the most widely found species in severely polluted settings. Species such as Gelidium sesquipedale, Heterosiphonial plumosa, Calliblepharis ciliata, Halopitys incurvus, Dictyopteris polypodioides and Halurus equisetifolius are species typically found at the reference site and are good indicators of unchanged environments. Pterosiphonia complanata, abundant at the reference site, took the place of G. sesquipedale in those sites farthest from the source of pollution. Ordination and classification analyses detected changes in flora after 8 yr, pointing toward a recuperating process. The improvement consisted of an increase in algal cover along with a decrease in ceramiaceous algae and a greater complexity in community stratification. This recovery was directly related to a decrease in industrial activity and closure of the mineral washeries, as well as the establishment of urban wastewater-treatment plants for various municipalities.