Morphology of the marine, planktonic, thecate dinoflagellate Gonyaulax areolata (Dinophyceae), a species causing red tides in the tropical Mexican Pacific.

Blooms of marine planktonic dinoflagellates are usual along the Pacific coast of Mexico, sometimes producing toxic red tides. The thecate dinoflagellate Gonyaulax areolata was found to produce a red tide event in the tropical Mexican Pacific. The species was originally described in 1911 by Kofoid and Michener without an illustration. The morphology of G. areolata was studied here by LM and SEM. Photosynthetic, solitary cells were fairly small, polyhedral, with a short apical protrusion and 'shoulders' on the epitheca, and two short, asymmetrical antapical spines. The cingulum was approximately median, cavozone, with the ends fairly displaced but with no, or only slight, overhang. The thecae were strongly ornamented with striae, areolae and pores. The plate formula was Po, 4ʹ, Q, 6ʹʹ, 6c, 4s, 6ʹʹʹ, 1p, 1ʹʹʹʹ, as recently attributed to some species of Gonyaulax. Details of important plates are given. Gonyaulax areolata seems to be morphologically closely related to other small species with a slight cingulum displacement and overhang, such as G. minima and G. striata, and more distantly related to G. spinifera. The maximum concentration of G. areolata was 1.74 × 106 cells l–1, in association with lower numbers of other dinoflagellates and diatoms. Yessotoxins were not detected. Oceanographic conditions during the bloom indicated moderate to weak upwelling, confirmed by both relatively low surface temperature and high Chl a concentration (14 µg l–1). [ABSTRACT FROM AUTHOR]