Observations on bio-optical properties of a phytoplankton bloom incoastal waters off Cochin during the onset of southwest monsoon.

Abstract

A phytoplankton bloom dominated by Chaetoceros spp. was detected in the Arabian Sea off Cochin coast during May 2009 coinciding the onset of Southwest monsoon with an average chlorophyll a concentration of 8.42 mg m^-3 at four stations (A,C,D&E) of total 7 stations studied in coastal waters situated between latitudes 9degree54'-10 degree 02' N and longitudes 76 degree05'-76degree12'E. All the stations were resampled after seven days and found that the average chlorophyll a concentration at the bloom stations has decreased to 2.91 mg m^-3. The inherent optical properties (chlorophyll a, specific phytoplankton absorption coefficient, chlorophyll scattering coefficient) of water were analyzed from the study area. The physiochemical parameters like Dissolved oxygen, PH, turbidity and nutrients were estimated for surface waters in these stations using standard methods. The phytoplankton of the study area was identified and their density was recorded. The phytoplankton community composed primarily of diatom Chaetoceros sp. in all the stations, with a percentage composition greater than 55 at the bloom. The highest phytoplankton density recorded was 4,89,578 cell no/1 at station D. Samples from the bloom showed higher specific phytoplankton absorption coefficient