On the Occurrence of Trichodesmium Erythraeum (Ehr.) Bloom in the Coastal Waters of Kalpakkam, East Coast of India

A prominent discolouration of the coastal waters by the blue-green alga Trichodesmium erythraeum was encountered in the east coast of Kalpakkam on 16th March 2007. The bloom persisted only for one day exhibiting visible alteration in physico-chemical properties and phytoplankton community structure of the coastal waters. The Trichodesmium cell density was 4.14 x 10 6 cells l -1 , sharing 74.19 % of the total cell count (5.57 x 10 6 cells l -1 ). Only 24 species of phytoplankton were encountered on the day of bloom as compared to the highest number of 44 species in a single observation during pre- and post-bloom periods (1st March to 29th March). Concentration of chlorophyll-a and phaeopigments increased to about 20 times on the day of bloom compared to the pre-bloom values. An abrupt increase in ammonia, total nitrogen and phosphate was noticed on the day of bloom. The impact of this bloom on coastal water quality is reported.