Comparison of structural and functional stability of polychaete assemblages in coastal lagoons

The loss of species is known to have a negative effect on ecosystem functioning, but detailed mechanisms of this relationship are still far from being fully understood. Several hypotheses have been proposed in the past to explain the functional response of ecosystems to species loss, but many studies still rely on using community structure as a surrogate for ecosystem functioning. This study investigates how the spatio-temporal distribution patterns of polychaetes and their associated functional patterns in six Mediterranean coastal lagoons change under simulated scenarios of species loss. The results show that each lagoon responds differently to potential species loss: in stressed lagoons with few dominating species the change of patterns is extremely variable and unpredictable, whereas lagoons characterised by complementarity seem to be more robust towards changes. The patterns between community structure and functioning in each lagoon show strong similarities in the lagoons dominated by few species, but the patterns diverge in complementary communities. The findings highlight the importance of considering the ideosyncratic effects of species loss on ecosystem function as well as the risk of using structural patterns as surrogates for functional patterns when taking decisions at a managerial level.