Analysis of morphological classification and pigment indices of phytoplankton in high and low mountain tropical systems.

We analyzed morphological and pigment-based ordinations, individually and together, in phytoplankton assemblages from high and low mountain tropical streams. Pigment composition was classified according to physiological function, resulting in pigment indices that represented variation in functional and physiological states. These indices revealed differences in adaptive trends and chromatic strategies. In parallel, morphological traits such as greatest linear dimension, volume and surface area, presence of mucilage, heterocytes, gas vesicles (or aerotopes), silica walls, and flagella allowed the identification of different phytoplankton adaptation strategies in the high and low mountain tropical environments. Compared to the pigment ordination, a morphology-based functional group classification capturing functional variation in phytoplankton explained greater variation among the different environments. The morphological groups also explained a higher percentage of morphotype variance than pigment indices in ordinations, whereas their combination explained more variation than individually. The relationship between morphology and pigments reflected specific features such as a greater presence of phytoplankton with colonial forms and mucilage (Group VII) combined with a higher value of the protective carotenoid index in the high mountain lake with high transparency, whereas this same index showed a negative relationship when the flagellated forms (Group V) were dominant in floodplain lakes of lowlands. Thus, the use of several ordinations allowed the identification of differences in the combination of morphological and pigment-based strategies in these tropical systems.