DISTRIBUTION OF CHROOCOCCOID CYANOBACTERIA AND SIZE-FRACTIONATED CHLOROPHYLL A BIOMASS IN THE CENTRAL AND SOUTHERN NORTH-SEA WATERS DURING JUNE JULY 1989

The spatial and vertical distribution of phycoerythrin(PE)-containing chroococcoid cyanobacteria and the contribution of the <3 mum size fra ction to overall phytoplankton chlorophyll a biomass were investigated in the central and southern North Sea during June and July 1989. PE-c ontaining chroococcoid cyanobacteria cell numbers ranged between 6x10( 5) and 4.4x10(7) cells.dm-3 and was typically between 0.5x10(7) and 3x 10(7) cells.dm-3, lowest numbers being recorded near the British coast in central North Sea waters. The vertical distribution of these cyano bacteria showed no evidence to suggest a preferential accumulation dee p in the euphotic zone. The <3 mum size fraction accounted for 6.6 to 57.5% of the total phytoplankton chlorophyll a biomass (mean 19.7%). I n general, the relative significance of the <3 mum size fraction decre ased with increasing total chlorophyll a biomass.