Phytoplankton composition in Mediterranean confined coastal lagoons: testing the use of ecosystem metabolism for the quantification of community-related variables

Estimations of ecosystem metabolism have rarely been used to quantify productivity in structural reductionist approaches for the description of phytoplankton composition. However, estimations of ecosystem metabolism could contribute to a better understanding of the relationship between phytoplankton composition and ecosystem functioning. To examine this, we investigated the community structure of phytoplankton in a set of Mediterranean coastal lagoons (natural and artificial) during a hydrological cycle to identify the most important environmental variables determining phytoplankton species composition. The focus of the study was on the quantification of productivity-related variables using estimations of ecosystem metabolism, such as different proxies for the estimation of the production-to-biomass ratio and of the relative importance of K- and r-strategies, which are commonly used conceptually but not quantified. Our results demonstrated differences in phytoplankton composition between seasons, due to the dominant hydrological pattern of flooding confinement in the salt marsh, and between lagoons that were caused by different levels of nutrient availability. Moreover, there was a notable decrease in the production/biomass ratio and a prevalence of K-strategists with seasonal succession, as predicted by Margalef’s mandala. Thus, the results showed that estimations of ecosystem metabolism are useful for the higher frequency quantification of important ecological variables, and contribute to a better understanding of planktonic assemblages, and physical and chemical changes, in these fluctuating ecosystems.