Aliphatic hydrocarbon pollution and macrobenthic assemblages in Ceuta harbour: a multivariate approach

The aliphatic hydrocarbon composition of sediments from Ceuta harbour, North Africa, was studied to determine the sources, levels and effects of these hydrocarbons on macrofauna composition by considering indices and concentration ratios in multivariate analyses. A total of 21 stations (15 inside and 6 outside the harbour) were sampled using a van Veen grab. High hydrocarbon concentrations (496 to 6972 ppm), the dominance of the UCM (unresolved complex mixture) in relation to the resolved alkanes, and values close to the unity (≈1) of the CPI (carbon preference index) and pristane:phytane ratio indicated anthropogenic origins of the hydrocarbons. Ceuta harbour is characterised by intense traffic, and frequent loading and dumping related to shipping operations. Furthermore, 2 urban effluent outfalls of Ceuta city flow into the harbour. The relationship between macrofauna and the above-measured parameters was evident in canonical correspondence analysis (CCA). Variation in species composition at different sample stations was related to the ratios of maltenes to other hydrocarbons, pristane:phytane and, especially, maltenes:asphaltenes, which turned out to be the main factor discriminating between internal and external stations according to species distribution. The crustaceans Corophium runcicorne and C. sextonae, the mollusc Parvicardium exiguum and the polychaete Pseudomalacoceros tridentata were only found at internal stations, while the polychaetes Jasmineira elegans and Scoloplos armiger were present only at external stations. The abundance of the crustaceans Apseudes latreilli, Leptochelia dubia and Pariambus typicus, and the polychaetes Capitella capitata, Nereis falsa and Potamilla reniformis, differed significantly between the internal and external stations. Although the asphaltene fraction is potentially hazardous to sediment macrofauna, due to its high molecular weight and its slow degradation, the relationship between the distribution of marine organisms and the presence of asphaltenes has never been explored in previous studies.