OBSERVATION OF SAND-DWELLING TOXIC DINOFLAGELLATES (DINOPHYCEAE) FROM WIDELY DIFFERING SITES, INCLUDING TWO NEW SPECIES.

Dinoflagellate associations, including toxic and potentially toxic benthic species, were examined in sand from South Water Cay and Carrie Bow Cay, Belize. The inshore sand habitat in localized areas of warm shallow lagoonal waters supported blooms of toxic assemblages of dinoflagellates. In the sand, the dominant microalgae were dinoflagellates; cyanobacteria were a minor component and diatoms were absent. Ciliates and nematodes were present. Assemblages of microorganisms in colored sand were examined for 4 consecutive days after which a storm washed away the patch. The sand-dwelling dinoflagellate assemblage included 16 species where densities ranged from as low as 1.3% to 15% of total cell densities. The dominant species was Scrippsiella subsalsa, having 1.8 × 10[sup5] to 2.3 × 10[sup5] cells · g[sup-1 sand. Toxic dinoflagellates indentified in the sand were Gambierdicus toxicus, Ostreopsis lenticularis, Prorocentrum lima, Prorocentrum mexicanum, and Amphidinum carteri. The potentially toxic Ostreopsis labens, Gambierdiscus belizeanus sp. nov., and Coolia tropicalis sp. nov. were also identified. Toxic and potentially toxic species represented 36% to 60% of total microalgal cell assemblage. The morphology of a new sand-dwelling species, Gambierdiscus belizeanus sp. nov., was examined with the scanning electron microscope. The plate formula was P[subo], 3′, 7′′, 6c, 8s?, 5′′′, 1p, and 2′′′′. Dimensions of G. belizeanus cells were 53-67 μm long, 54-63 μm wide, and 92-98 μm in dorsoventral depth. Cells were deeply areolated, ellipsoid in apical view, and compressed anteroposteriorly. The cells of G. belizeanus were identified by the cell's long, narrow, pentagonal, posterior intercalary plate (1p) wedged between the wide postcingular plates 2′′′ and 4′′′; 1p occupied 20% of the width of the hypotheca. The plate formula for Coolia tropicalis sp. nov. was P[subo], 3′, 7′′, 7c, 8s?. 5′′′, and 2′′′′. Cell size ranges were 23-40 μm long, 25-39 μm wide, and 35-65 μm in dorsoventral diameter. Cells were spherical, smooth, and covered with scattered round pores. The epitheca was smaller than the hypotheca. Precingular plates 1′ and 7′′ were small and narrow, and the first apical plate 1′ and precingular plate 6′′ were the largest plates on the epitheca. The apical pore was straight and 7 μm long, and was situated in the apical plate complex. Cells of C. tropicalis were distinguished from C. monotis by the wedge-shaped plate 1′, a four-sided 3′ plate, and a short apical pore. [ABSTRACT FROM AUTHOR]