An analytical study of the role of various factors causing red tide outbreaks of trichodesmium as deduced from field and laboratory observation.

The marine blue green alga Trichodesmium sp is found in red-tide outbreaks in sub-tropical areas in the Pacific and Indian Oceans, the Arabian Seas and the equatorial currents of the Gulf of Mexico. Giberellic acid stimulated the growth of Trichodesmium cultures to a greater extent than in the diatom Melosira sulcata. While increasing either the nitrate or phosphate above the normal levels in the culture medium did not greatly stimulate the growth of this organism, Trichodesmium did thrive in nitrogen impoverished waters by nitrogen fixation. The relevance of these findings to the hydrological factors which favour red-tide outbreaks is discussed.