Macroalgal fouling communities as indicators of environmental change: potential applications for water quality monitoring

Macroalgal fouling communities are potentially useful as bioindicators in environmental monitoring as they are considered to be sensitive to changes in environmental conditions and the use of artificial substrata facilitates the implementation of standardized sampling strategies. The response of macroalgal fouling communities on buoys to changes in water quality was investigated with a view to the possible utilization of these assemblages in environmental monitoring programmes. Seven study sites were selected based on previously collected environmental data and Principal Components Analysis (PCA) was used to order sites according to beam attenuation coefficient (BAC) and concentration of dissolved nitrates and phosphates, relative to a minimally impacted reference site. At each site, all fouling macroalgae were collected from 10 buoys of standard shape and size, and were identified to the lowest possible taxonomic level. Species composition and species dominance were highly variable among impacted sites, indicating that qualitative aspects of community structure may not be useful as indicators of changes in water quality. However, higher levels of nutrient enrichment and turbidity were associated with lower macroalgal species richness, lower overall abundances, and decreased diversities, and therefore these quantitative aspects of community structure are potentially useful as indicators of environmental change. Intermediate levels of turbidity and nutrient enrichment were associated with lower evenness, but did not influence species richness, suggesting that macroalgal abundances respond to changes in environmental conditions before species replacement occurs.