Annual cycle of particle size fractions and phytoplankton biomass in the northern Baltic proper

Abstract

A larqe data set of particle concentrations in the ranqe 1 to 1000 rrm, chloro~hvll a, and . . associated measur&nents from the surface waters of the northern ~iitic Drooer durino 1985 to 1989 was . . a ~~~ ~ ~~~~ ~~ anilly7~!d to roncrruct spdlially and temporally averaged annual rlnle curvrs of pdrrlrlr size fractions and phytoplanklorl Im,rnasi. Chlorophyll a concenrratlon wdz wrll t.c,rr~.l,atrrl wlrh the 28-73 -m s.ze lractron and had 2 seasonal peaks: in A~I-M~~, corresponding to the diatom spring bloom, and in August, corresponding to the late-summer bloom of blue-green algae. The 2 maxima were separated by the early summer minimum when the 1-10 p particle fractions corresponding to a mixed assemblage of small phytoplankton and microheterotrophs reached their maxima. The largest particles (163-1000 p), corresponding to smaller mesozooplankton, reached their maximum in July-August before the blue- green maximum. Automated particle counting is well suited for routine monitoring of pelagic systems as it reveals all major shifts in the planktonic community.