| dc.description.abstract | Particulate carbohydrates (PCHO) and proteins (PP) of the offshore waters (depth greater than 200 m) were measured within the upper 150 m water column along the six transects covering 36 stations perpendicular to the coast in the Bay of Bengal. Concentrations of PCHO and PP ranged from 31 to 158 mu g l sup(-1) and from 0.56 to 2.45 mu g atomic (at) N l sup(-1) at the surface, and decreased to 7-58 mu g l sup(-1) and 0.43-1.62 mu g at N l sup(-1) at 150 m depth, respectively. In surface waters, the concentrations of these particulates showed high nearshore values with a pronounced seaward decrease, whereas subsurfce concentrations did not reveal any particular trend. Regressions indicated that the detrital component may be in the form of terrigenous organic matter, and decomposition of plankton constituted a major fraction of particulate organic matter (POM). Subsurface chlorophyll maxima (SCM) were a consistent feature which occurred between 50 and 80 m. Chlorophyll a (Chl a) content in the SCM was twice the observes surface values. A maximum Chl a/ PP-N ratio of 0.48 plus or minus 0.07 mu g Chl mu g at N sup(-1) was recorded in the SCM, indicating that phytoplankton comprise a major proportion of biomass in the SCM. Furthermore, comparison of Chl a) PP-N ratios in the 150 m water column with those observed from other regions (oligotrophic and eutrophic), in addition to phytoplankton cultures, suggests that the Bay of Bengal appears to be oligatrophic rather than eutrophic, with a much higher contribution of non-plant material to the total biomass. Phytoplankton accounted for between 2.4 and 23% of the total carbohydrates, while its contribution to the protein pool ranged from 2 to 20% reflecting a proportion of phytoplankton in the seston. Ratios of PP/PCHO as a means of estimating plankton nutritional status indicated a severe lack of nitrogen or phosphorus deficiency. However, this ratio may not serve as a true indicator of nutrient deficiency in oligotrophic areas, where non-phytal biomass controls the distribution of particulate concentrations | |
