Chlorophyll a of Size-fractionated Summer Phytoplankton Blooms at a Coastal Station in Málaga Bay, Alboran Sea

The chlorophyll a content of four different size fractions (<2, 2-20, 20-45, 45-100 μm) of phytoplankton at a coastal station of Málaga Bay (South Spain) were studied throughout the summer and autumn of 1989. Pigment concentrations in the surface of sediments were also measured. Episodes of increased chlorophyll a concentration revealed the transitory existence of several blooms. The large increases in biomass consisted mostly of nanoplankton (2-20 μm) and this generally represents some 50% of the chlorophyll a. Forty percent of the chlorophyll was distributed equally between the two particle-size classes <2 μm and 20-45 μm. Only 10% was found in the 45-100 μm particle-size class. When the plankton blooms were particularly intense, the rapid sedimentation of a large amount of cells is clearly indicated by the transitory increases of the chlorophyll a in the sea-bottom sediments.