Blooming of the dinoflagellates Noctiluca scintillans was observed at Kollam Bay, Kerala during September 2003 (bloom-1) and Cochlodinium sp. in September 2004 (bloom-2) with cell densities of 9.8 x 104 and 1.4 x 105 cells l-1 respectively. These caused 27% and 100% mortality of the farmed pearl oyster Pinctada fucata in the raft farms of Central Marine Fisheries Research Institute moored in the Bay. The mortality of
the pearl oysters can be attributed to the high dissolved ammonia 14.9 μmol l-1 during bloom-1 and high dissolved ammonia (14.7 μmol l-1) and total suspended solids (154.8 mg l-1) during bloom-2. These
instances of harmful algal blooms (HAB) indicate that precautionary management protocols should be developed to relocate the farm stock to overcome such natural causes to prevent economic loss to farmers.

Noctiluca scintillans, Cochlodinium sp., harmful algal blooms (HAB), farmed pearl oysters