Harmful algae are microscopic, single-celled plants that live in the sea. Most species of algae or phytoplankton are not harmful and serve as the primary producers of the oceanic food-web. Occasionally, the algae grow very fast or "bloom" and accumulate into dense, visible patches near the surface of the water. "Red Tide" is a common name for such a phenomenon.
         Only a few dozen of the many thousands of species of microscopic and macrosc-opic algae are reportedly associated with toxic or harmful blooms. Some species, such as the dinoflagellate Alexandrium, Gymnodinium, Pyrodynium, Dinophysis and diatom Ps-eudonitzschia etc. produce potent toxins that are transferred through the food web and affect or even kill higher forms of life such as shellfish, fish, birds and marine mammals including humans that feed either directly or indirectly on them.

In all 761 stations have been covered sofar to study the distribution of toxic algae in the Indian EEZ. A total of 392 species (206 species of diatoms, 164 dinoflagellates, 16 blue green algae, 6 other groups- Silicoflagellates, Chlorophytes, Coccolithophorids and Prasinophytes) have been recorded from the Arabian Sea and Bay of Bengal.

Of the 164 species of dinoflagellates identified, 13 species were found toxic and 8 species harmful. Among the diatoms only two species of Pseudonitzschia were toxic whereas 14 species were identified as harmful. So far 19 major oceanic blooms have been documented in the Indian EEZ. Efforts to isolate algal cysts from sediment have met with success with the modified isolation procedures employed. Also sequence information to resolve taxonomic ambiguity of Trichodesmium species from Indian waters have been generated underthe on-going activit

Some species which are not toxic to humans, are harmful to fish and invertebrates as they damage or clog the gills causing irritation, over production of mucous, and eventual death (eg. diatom Chaetoceros, dinoflagellate Gymnodinium, Prymnesiophyte). Other species of bloom farming algae deplete the surface waters of dissolved oxygen, nutrients etc. and are thus harmful to other organisms.

In this context, CMLRE, Ministry of Earth Sciences, Kochi is implementing a programme for Monitoring and surveillance of Harmful Algal Bloom in and around Indian EEZ. The HAB programme envisage surveillance and monitoring of algal bloom in the Indian EEZ and study the cause for the formation, growth and crashing of the blooms. The overall objective is to develop prediction capabilities on HAB and to mitigate the adverse effects of such blooms on aquaculture farms, coastal waters and open ocean.