Structural and Functional Responses of Macrobenthic Communities to Mercury Contamination

Abstract

This study focuses on the impact of mercury contamination on the structure and functioning of the macrobenthic communities of Ria de Aveiro (Portugal), using secondary production as an indicator of population fitness. Through the implementation of this new approach which combines the static and dynamic variables of a population, it is possible to better understand ecosystems’ responses to external stressors. For that, a monthly monitoring programme was implemented at three different contaminated sites and data collected was analysed combining structural and functional levels. A permutational multivariate analysis of variance (PERMANOVA) detected significant differences in macrobenthic assemblages between the three sampling sites along the mercury gradient. The most contaminated area was characterized by low biomass and species richness, while the least contaminated one presented slightly higher values. A significant negative correlation was observed between mercury concentration in the sediments and biomass of macrobenthic species (r = −0.50; P < 0.05). However, species diversity (heterogeneity) and total secondary production presented irregular patterns in response to mercury contamination. In the present study, the highest values of total biomass and secondary production were, curiously, observed in the intermediate contaminated area, followed by the least contaminated site and finally the most contaminated one. This response seems to be related to the hormesis phenomenon. Moreover, distinct taxonomic and trophic groups showed different responses to mercury contamination, while body size was the trait that best responded to the contaminant stressor.