Assessing functional diversity of macrobenthic assemblages in sewage-affected intertidal shores

Functional diversity is the component of diversity that influences ecosystem dynamics, stability, productivity, nutrient balance, and other aspects of ecosystem functioning. We evaluate the spatio-temporal variability of the functional traits (biological traits analysis), functional diversity indices (functional richness, functional evenness, functional divergence and functional dispersion) and AZTI marine biotic index in response to the distinct levels of sewage contamination at different sites on intertidal abrasion platforms. Variations in macrobenthic functional structure between reference and impacted sites were evident in the study area. The functional richness showed a pattern with higher values in the reference sites; Functional evenness showed a similar pattern, but only during spring. Functional divergence presented lower values in the impacted sites during autumn and spring. The functional diversity indices (functional richness and functional evenness) and the AZTI marine biotic index presented a negative relationship, indicating that functional diversity is related to benthic environmental health. Thus, biological traits analysis and functional diversity indices, especially FRic that reveals differences in macrobenthic functional structure between impacted and reference sites during all seasons, represent an informative and useful tool to describe the different aspects of sewage impacts in benthic assemblages on rocky shores. These analyses have a high potential for future monitoring programmes.