Phytoplankton biomass and production in the coastal water off Goa, West Coast , India.

Abstract

The coastal water off Goa is a characteristically interesting marine environment due to influence of the monsoon and upwelling. Studies on the primary productivity and related areas revealed the following results. - Water column is stratified during October and remained well mixed during November. - Hypoxic condition prevailed at the bottom during October but not in November. - Nutrients (especially Nitrate) was low during October (surface) but increased during November. High nutrients remain in bottom largely due to intense stratification during October. - Phytoplankton biomass (Chl a) average was high during October of 2.34 mgm^3 and in November it was as low as 0.62 mgm-3. - Chl a at 30m depth was as high as 1.03 mg m-3 and that of November it was 0.43 mgm^-3. - Primary Production during October (Surface) was 612.62 mgCm-3 day-1 and that in column was 14.96 gCm^-2day^-1. During November surface productivity was 219 mgCm-3day-1 and that of column was 4.13 gCm-2day-1. - In fractionation study picoplankton contributed 35.75% of total Chl a.However, in Primary production picoplankton contributed 92.54% of the total production at the surface during October. Total 46 species of phytoplankton were observed in the study area and major being diatoms (i.e. 33 species) and 13 species of dinoflagellates. Chemotaxonomic studies also indicated diatoms domination in whole sample as well as in fractions of <10 microns dominated by picoplankton.Most importantly the coastal water off Goa remained well stratified during October month and well mixed during November month. Due to this, Chl a during October is high compared to that in November. This is in agreement with nutrient data during October and November months. The sample taken from the 30m depth demonstrated negligible productivity although Chl a is measurably high. The carbon production at the surface water was much more during October (612.62 mgCm-3 day-1) compared to November (219.1 mgCm^-3day^-1). The factors responsible for lower production are water column stability and availability of light in the coastal water off Goa.