The effect of different levels of anthropogenic impact on marine macroalgal fouling assemblages in the Maltese Islands

Abstract

The aim of this study was to test the hypothesis that different degrees of anthropogenic impact have an effect on the species richness, composition and abundances of the macroalgal component of marine fouling assemblages in the Maltese Islands. Eight study sites were selected based on previously collected environmental data. Principal components analysis (PCA) was used to order sites according to beam attenuation coefficient (BAC), and nitrate and phosphate concentration, in relation to a minimally impacted reference site. At each site, ten spherical buoys of circumference 70 – 90 cm were selected and all fouling macroalgal species were collected from each buoy and identified to the lowest possible taxonomic level. The taxa identified were subsequently dried to obtain values of dry biomass. The Phylum Rhodophyta accounted for 60 % of all macroalgal genera encountered, and the proportions of each phylum (Rhodophyta, Chlorophyta, Ochrophyta and Cyanobacteria) present did not vary between locations. The locations sampled were dominated by filamentous or coralline macroalgae; filamentous forms are annual, opportunistic species which are tolerant to physical and biotic stress, while coralline forms are able to survive unfavourable environmental conditions and can recover rapidly after disturbances. Lower levels of nutrient enrichment and turbidity were associated with higher macroalgal species richnesses, abundances and diversity. Locations which were considered to be impacted all differed from each other both in terms of genus composition and in terms of abundances, indicating that macroalgal fouling assemblages may be influenced by factors other than those considered here. The results of this investigation indicate that macroalgal species richness, abundance and diversity in fouling communities on buoys were influenced by the abiotic factors considered. Therefore, macroalgal fouling communities on buoys could potentially be used for water quality monitoring in the Maltese Islands. Conversely, aspects of community structure such as macroalgal taxon dominance and functional form composition may not be applicable in the local context as indicators of water quality.