Functional groups in marine phytoplankton assemblages dominated by diatoms in fjords of southern Chile

The co-existence of phytoplankton assemblages under similar environmental conditions has allowed the identification of functional groups made up of species with similar morphological and physiological characteristics. Species belonging to similar functional groups in turn can be grouped in the three basic adaptive strategies C (colonist-invasives), S (stress-tolerants) and R (ruderals), these strategies being based on the species tolerances to different combinations of the degree of mixing and nutrient availability. In this study, we evaluated the applicability of the C–S–R strategies approach to marine diatom-dominated phytoplankton assemblages from fjords of southern Chile. Surface/volume ratios (S/V) and maximum linear dimensions were used to group the species in the three strategies regardless of their phylogenetic relationships. Multivariate statistical analyses (multiple correspondence and canonical correspondence) allowed us to identify three diatom groups. Group D1, made up of species with S/V > 1.5 μm−1 (Pseudo-nitzschia spp. group delicatissima, Cylindrotheca closterium, Leptocylindrus minimus), was correlated mainly with nitrate concentrations. In group D2, several species of the genus Chaetoceros (S/V ∼ 1 μm−1) were also correlated with nitrate. Species with attenuated forms and S/V ranging between 0.5 and 0.8 μm−1 (Skeletonema costatum, Talassionema nitzschioides, Rhizosolenia setigera) made up group D3, which was associated with stratified conditions and high silicate.