Prorocentrals are epiphytic organisms on various substrates, including Thalassia testudinum; Due to its relationship with the production of toxins that cause poisoning, it was proposed to analyze the variation of these organisms, associated with T. testudinum, during the upwelling and relaxation season, at La Maceta beach, Boca del Río. For this, during the period January-April (emergence) and June-September (relaxation) of the year 2017, monthly samples of T. testudinum were taken in four zones. Dinoflagellates were separated from the plants and then fixed with formalin at 10%. Using a modification of the Utermöhl method, the abundance of Prorocentrals, their spatial and seasonal variation, was determined through the PERMANOVA statistical test. Of the 32 samples analyzed, the genus Prorocentrum was the only representative of the order Prorocentrals, identifying 10 species, being P. compressum the most abundant (2167.42 cells/g dry weight). Significant differences were recorded in terms of abundance by season, obtaining the highest values in the upwelling period (average abundance 195.05 ± 32.40 cells/g dry weight).
No such differences were detected between the sampling areas. The evidenced behavior corresponds
to the characteristic pattern of primary production during the upwelling season, a period during which
surface waters are fertilized, benefiting the abundance of microalgae. T. testudinum seems to be a favorable
substrate for the settlement of Prorocentral communities, its presence and abundance may be limited by
the resuspended sediment that is deposited on the phanerogams, thus reducing the surface available for
the organisms.
