OBSERVATION OF SAND-DWELLING TOXIC DINOFLAGELLATES (DINOPHYCEAE) FROMWIDELY DIFFERING SITES, INCLUDING 2 NEW SPECIES

Dinoflagellate associations, including toxic and potentially toxic ben thic species, were examined in sand from South Water Cay and Carrie Bo w Gay, Belize. The inshore sand habitat in localized areas of warm sha llow lagoonal waters supported blooms of toxic assemblages of dinoflag ellates. In the sand, the dominant microalgae were dinoflagellates; cy anobacteria were a minor component and diatoms were absent. Ciliates a nd nematodes were present. Assemblages of microorganisms in colored sa nd were examined for 4 consecutive days after which a storm washed awa y the parch. The sand-dwelling dinoflagellate assemblage included 16 s pecies where densities ranged from as low as 1.3% to 15% of total cell densities. The dominant species was Scrippsiella subsalsa, having 1.8 x 10(5) to 2.6 x 10(5) cells . g(-1) sand. Toxic dinoflagellates iden tified in the sand were Gambierdiscus toxicus, Ostreopsis lenticularis , Prorocentrum lima, Prorocentrum mexicanum, and Amphidinium carteri. The potentially toxic Ostreopsis labens, Gambierdiscus belizeanus sp. nov., and Coolia tropicalis sp, nov. were also identified. Toxic and p otentially toxic species represented 36% to 60% of total microalgal ce ll assemblage. The morphology of a new sand-dwelling species, Gambierd iscus belizeanus sp. nov., was examined with the scanning electron mic roscope. The plate formula was P-o, 3', 7 '', 6c, 8s?, 5''', 1p, and 2 ''''. Dimensions of G. belizeanus cells were 53-67 mu m long, 54-63 mu m wide, and 92-98 mu m in dorsoventral depth. Cells were deeply areol ated, ellipsoid in apical view, and compressed anteroposteriorly. The cells of G. belizeanus were identified by the cell's long, narrow, pen tagonal, posterior intercalary plate (1p) wedged between the wide post cingular plates 2''' and 4'''; 1p occupied 20% of the width of the hyp otheca. The plate formula for Coolia tropicalis sp. nov. was P-o, 3', 7 '', 7c, 8s?, 5''' and 2''''. Cell size ranges were 23-40 mu m long, 25-39 mu m wide, and 35-65 mu m in dorsoventral diameter. Cells were s pherical, 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 str aight and 7 mu m long, and was situated in the apical plate complex. C ells of C. tropicalis were distinguished from C. monotis by the wedge- shaped plate 1', a four-sided 3' plate, and a short apical pore.