CHANGES IN THE SUBLITTORAL BENTHIC MARINE MACROALGAE IN THE POLLUTED AREA OF ABRA-DE-BILBAO AND PROXIMAL COAST (NORTHERN SPAIN)

Sublittoral communities of macroalgae from the Abra de Bilbao and its surrounding area, which are affected by pollution, were studied in 198 4 and 1992. Statistical cluster analysis applied to a network of 230 q uadrats distributed along 7 transects resulted in 4 structural levels of community, depending on the pollution gradient. These levels are de fined by algal cover, vertical layering and the predominant morphology of the species forming the community. Sedimentation, turbidity and wa ter toxicity are the principal destabilizing factors among the phytobe nthic communities. Species with simple morphology, mainly ceramiaceous algae (Ceramium diaphanum, Callithamnion neglectum, Antithamnionella spirographidis, Pterothamnion plumula, Anotrichium furcellatum, Compso thamnion thuyoides), sciaphilous (Mesophyllum lichenoides, Zanardinia prototypus, Rhodymenia coespitosella, Drachiella minuta, Erythroglossu m laciniatum, Hypoglossum hypoglossoides) and those resistant to sedim entation (Pterosiphonia pennata and Champia parvula) are the most wide ly found species in severely polluted settings. Species such as Gelidi um sesquipedale, Heterosiphonia plumosa, Calliblepharis ciliata, Halop itys incurvus, Dictyopteris polypodioides and Halurus equisetifolius a re species typically found at the reference site and are good indicato rs of unchanged environments. Pterosiphonia complanata, abundant at th e reference site, took the place of G, sesquipedale in those sites far thest from the source of pollution. Ordination and classification anal yses detected changes in flora after 8 yr, pointing toward a recuperat ing process. The improvement consisted of an increase in algal cover a long with a decrease in ceramiaceous algae and a greater complexity in community stratification. This recovery was directly related to a dec rease in industrial activity and closure of the mineral washeries, as well as the establishment of urban wastewater-treatment plants for var ious municipalities.