PARTICULATE CARBOHYDRATE AND PROTEINS IN THE BAY-OF-BENGAL

Particulate carbohydrates (PCHO) and proteins (PP) of the offshore wat ers (depth > 200 m) were measured within the upper 150 m water column along the six transects covering 36 stations perpendicular to the coas t in the Bay of Bengal. Concentrations of PCHO and PP ranged from 31 t o 158 mu g l(-1) and from 0.56 to 2.45 mu g atomic (at) N l(-1) at the surface, and decreased to 7-58 mu g l(-1) and 0.43-1.62 mu g at N l(- 1) at 150 m depth, respectively. In surface waters, the concentrations of these particulates showed high nearshore values with a pronounced seaward decrease, whereas subsurface concentrations did not reveal any particular trend. Regressions indicated that the detrital component m ay be in the form of terrigenous organic matter, and decomposition of plankton constituted a major fraction of particulate organic matter (P OM). Subsurface chlorophyll maxima (SCM) were a consistent feature whi ch occurred between 50 and 80 m. Chlorophyll a (Chl a) content in the SCM was twice the observed surface values. A maximum Chi a/PP-N ratio of 0.48 +/- 0.07 mu g Chl mu g at N-1 was recorded in the SCM, indicat ing that phytoplankton comprise a major proportion of biomass in the S CM. Furthermore, comparison of Chl a/PP-N ratios in the 150 m water co lumn with those observed from other regions (oligotrophic and eutrophi c), in addition to phytoplankton cultures, suggests that the Bay of Be ngal appears to be oligotrophic rather than eutrophic, with a much hig her contribution of non-plant material to the total biomass. Phytoplan kton accounted for between 2.4 and 23% of the total carbohydrates, whi le its contribution to the protein pool ranged from 2 to 20% reflectin g a proportion of phytoplankton in the seston. Ratios of PP/PCHO as a means of estimating plankton nutritional status indicated a severe lac k of nitrogen or phosphorus deficiency. However, this ratio may not se rve as a true indicator of nutrient deficiency in oligotrophic areas, where non-phytal biomass controls the distribution of particulate conc entrations. (C) 1996 Academic Press Limited