Removal and Temporary Cyst Formation of Gymnodinium catenatum (Dinophyceae) Using Calcium Bentonite Clay and Zeolite

Clay minerals and other flocculants are used to mitigate the effects of some species that produce harmful algal blooms due to their physical and chemical characteristics. In this study, we applied calcium bentonite clay (Bca) and zeolite (Ze) to flocculate and remove cells of the dinoflagellate Gymnodinium catenatum (Graham), a producer of paralyzing toxins. The flocculants were characterized by scanning electron microscopy (SEM) in combination with an energy-dispersive X-ray spectroscopy (EDS) microanalysis system. During experiments, Bca and Ze were suspended in distilled water, deionized water, and seawater at concentrations of 0.25, 0.5, 1.0, 1.5, 2.0, 2.5, and 4.0 gL−1. The percentage of removal efficiency (RE%) of biomass indicators of G. catenatum was calculated. The cell number and concentration of chlorophyll a and peridinin were analyzed using high-performance liquid chromatography (HPLC-UV and HPLC-DAD). The external effects on cells of G. catenatum were recorded. As a result, the maximum RE% of Bca was 79% with respect to the total number of cells, chlorophyll a was 69% and peridinin of 73%. The RE% of Ze was less than 40%. In the matrix of sedimented Bca, malformation of cells was observed, inhibiting their swimming, as well as death and rupture of cells with temporary cyst formation after 72 h. We conclude that Bca, suspended in deionized and distilled water, was more efficient in flocculating cells of G. catenatum.