Marine eutrophication and benthos: the need for new approaches and concepts

In this review, using examples drawn from field observations or experimental studies, our goals are (i) to briefly summarize the major changes, in terms of species composition and functional structure, occurring in phyto and zoobenthic communities in relation to nutrient enrichment of the ecosystems; particular interest is given to the major abiotic and biotic factors occurring during the eutrophication process, (ii) to discuss the direct and indirect influences of benthic organisms on eutrophication and whether the latter can be controlled or favoured by benthos; most benthic species play a major role in the process of benthic nutrient regeneration, affecting primary production by supplying nutrients directly and enhancing rates of pelagic recycling; experimental studies have shown that the impact of benthic fauna on benthic-pelagic coupling and nutrient release is considerable. Thus, once the eutrophication process is engaged-that is, high organic matter sedimentation-it may be indirectly favoured by benthic organisms; benthos should always be considered in eutrophication studies, (iii) to evaluate the limits of our observations and data, highlighting the strong need for integrated studies leading to new concepts. Coastal ecosystems and benthic communities are potentially impacted by numerous human activities (demersal fishing, toxic contaminants, aquaculture...); in order to design strategies of ecosystem restoration or rehabilitation, we have to better understand coastal eutrophication and develop tools for quantifying the impacts; in order to achieve this goal, some possible directions proposed are: integrated studies leading to new concepts, model development based on these concepts and finally comparison of various ecosystems on a global scale.