Phytoplankton assemblages in two compartmentalized coastal tropical lagoons (Carretas-Pereyra and Chantuto-Panzacola, Mexico)

During an annual cycle (2002–2003), spatio-temporal differences and/or similarities in phytoplankton communities and their relationship with physical and chemical characteristics were determined in two coastal lagoons on the Mexican South Pacific coast: Chantuto-Panzacola (CHP) and Carretas-Pereyra (CP), Chiapas. Phytoplankton assemblages, characteristic of the two main seasons (dry and wet), were identified using principal component analysis (PCA), while canonical correspondence analysis (CCA) was used to examine environmental variables that may explain the patterns of variation of the phytoplankton community. The results show that both systems have similar characteristics because they have the same physical forcing (river discharge, seawater intrusion and, in general, weather). Spatial variability is especially important because it favors, during each season, the development of two different functional zones: a marine influence zone (MIZ) and a freshwater influence zone (FIZ). Phytoplankton distribution, composition and abundance were influenced by this environmental variation. Based on PCA results, during the dry season, assemblages in these lagoons are mainly comprised of neritic diatoms such as Coscinodiscus spp. and Skeletonema costatum distributed in the MIZ, whereas dinoflagellates of the genus Protoperidinium spp., and brackish diatoms such as Cyclotella sp., Entomoneis alata and Surirella spp., make up FIZ assemblages. CCA analysis indicates that salinity, temperature, dissolved oxygen and ammonium were the most relevant environmental factors affecting the variation in the distribution of these assemblages. On the other hand, during the rainy season, assemblages were correlated with silicate and orthophosphate concentrations, while their composition was dominated by freshwater groups mainly in the FIZ, whereas in the MIZ centric diatoms were dominant. In summary, in CHP and CP coastal lagoons, phytoplankton assemblages undergo changes in species composition and community structure during each season in response to environmental variation, which allows the development of associations specifically adapted to prevailing conditions.