Seasonal phytoplankton composition of two coastal lagoons of the tropical Pacific

Abstract

This paper presents the seasonal composition and distribution of the microphytoplankton comunity collected during the period 1997-2002 in two coastal lagoons, Chantuto-Panzacola (CH-P) and Carretas-Pereyra (C-P), located in the state of Chiapas, Mexico. A total of 199 and 125 taxa were identified in CH-P and C-P respectively; in both systems more than 60% of the composition was represented by diatoms, followed in order of importance by dinoflagellates, chlorophytes, cyanophytes, euglenophytes, and finally by silicoflagellates. The results of a Principal Components Analysis (PCA) of stations, based on the presence/absence of species, generated the discrimination of two analogous zones for each system. These zones correspond with the environmental gradient generated by physical and chemical variables like salinity and nutrients which explain more than 70% of the variance and allow the differentiation of two groups of communities: during dry season there was a dominance of alocthonous (neritic) phytoplankton like diatoms and dinoflagellates, distributed mainly in the zone of greater tidal influence; in the rainy season the community was integrated by freshwater groups (chlorophytes, cianophytes, and euglenophytes) as well as of diatoms with brackish affinities (Surirella spp.).