Seasonal Variations in Plankton Pigments in Waters off Sydney

Abstract

Weekly determinations of pigments were made at two stations off Sydney in 1959 and 1960. There were several peaks in pigment concentration, particularly in February, August, September, and October. The highest concentrations were 7.42 mg/m³ chlorophyll a, 1.15 mg/m³ chlorophyll b, 6.11 MSPU/m³ chlorophyll c, 1 -39 MSPU/m³ astacin carotenoids, and 2.33 MSPU/m³ non-astacin carotenoids. The 50-m station gave higher values than the 100-m station (further from the coast). There was always less chlorophyll b than a, and usually more chlorophyll c than a. The phytoplankton biomass was calculated from total chlorophyll and varied from 100 to 2200 mg/m³. There was no complete exhaustion of nutrient salts; there were occasional intrusions of nutrient-rich slope water. Excluding periods of salp swarms the average phytoplankton biomass was three times the average zooplankton biomass. During the occasional salp swarms phytoplankton biomass was low. It is suggested that phytoplankton biomass was determined more by zooplankton than by nutrient levels.