Seasonal variation in chemical constituents of certain brown seaweeds and seawater from Saurashtra Coast: 1. Carbon, nitrogen and phosphorus

Abstract

The annual mean concentration of C, N and P in seawaters of Porbandar and Okha coasts varied from 2100-2500, 6.15-13.75 and 0.10-1.62 ug-at (super.l)-1 respectively. Depletion of P takes place during maximum biomass period, while no such marked depletion of N was noticed. The N:P values of whole seaweed probably indicate integrated concentrations of the ambient medium during the previous months. High C:N ratios were observed in senescent and slow growth stages followed by reproductive phase and early and rapid growth phases. Hence, C:N ratio variation in a seaweed population is attributable to their different phenological stages. The N:P atomic ratio trend is opposite to C:N trend in Cystoseira indica and Sargassum johnstonii with two reproductive stages in their life cycles (one year); whereas in Sargassum tenerrimum with single reproductive stage in its one year life cycle does not show this trend. The critical internal values for N and P for the aforementioned seaweeds in the field conditions were 1.84-2.05 and 0.10-0.16 dry wt. respectively