Comparison of chlorophyll <i>a</i> and carotenoids as predictors of phytoplankton biomass in the Cross River system of Nigeria

Abstract

Spectrophotometric determinations of chl a and carotenoids were carried out in Cross River system of south eastern Nigeria during 1 annual cycle (March 1988 - March 1989). Both pigments displayed significant seasonal variations. Correlation coefficients (r) for linear relationships between phytoplankton cell density and chl a on the one hand and between cell density and carotenoids on the other, were highly significant. However, a comparison of coefficients of determination (r2) for both linear correlations, revealed that 85% of the variance in chl a concentrations can be explained by variations in total phytoplankton cell density while cell density can only account tor 47% of variance in the concentration of carotenoids. A comparison of confidence intervals for coefficients of regression also showed that chl a would be a better predictor of phytoplankton standing crop in the river system. The differences in prediction capabilities of both pigments were attributed to seasonal changes in phytoplankton species composition which can have significant effects on carotenoids.