COMPARISON OF CHLOROPHYLL-A AND CAROTENOIDS AS PREDICTORS OF PHYTOPLANKTON BIOMASS IN THE CROSS RIVER SYSTEM OF NIGERIA

Spectrophotometric determinations of chl a and carotenoids were carrie d out in Cross River system of south eastern Nigeria during 1 annual c ycle (March 1988 - March 1989). Both pigments displayed significant se asonal variations. Correlation coefficients (r) for linear relationshi ps between phytoplankton cell density and chl a on the one hand and be tween cell density and carotenoids on the other, were highly significa nt. However, a comparison of coefficients of determination (r2) for bo th linear correlations, revealed that 85% of the variance in chl a con centrations can be explained by variations in total phytoplankton cell density while cell density can only account tor 47% of variance in th e concentration of carotenoids. A comparison of confidence intervals f or coefficients of regression also showed that chl a would be a better predictor of phytoplankton standing crop in the river system. The dif ferences in prediction capabilities of both pigments were attributed t o seasonal changes in phytoplankton species composition which can have significant effects on carotenoids.