Nutrient enrichment and variation in community structure on rocky shores: The potential of molluscan assemblages for biomonitoring

Consideration of the impacts of pollutants on elements of biodiversity and the development of cost-effective biomonitoring tools to measure those impacts are essential to coastal biodiversity conservation. To examine the effects of nutrient enrichment and to develop biomonitoring tools, a network of 11 rocky intertidal sites differing in nutrient contamination levels was established on the west coast of Ireland. Communities of molluscs on the lower shore were sampled at the sites and a range of physicochemical variables was measured to characterize levels of contamination on the shores. Total abundance and number of taxa of molluscs were reduced in contaminated sites compared to control sites. Multivariate analyses showed that the structure of the molluscan assemblages differed between contaminated and control sites, discriminating between species that were more abundant at contaminated sites and those that were more abundant at control sites. Multivariate multiple regression analysis showed that nitrite, phosphate and ammonia levels in seawater accounted for more than 45% of the variability in the community structure of molluscs. This study suggests that molluscan assemblages could be a cost-effective tool to monitor and detect changes induced by nutrient enrichment in coastal areas.