Vertical distribution of size-fractions in the zooplankton community in Lindåspollene, Western Norway. l. Seasonal variations

Abstract

Abstract Zooplankton were collected in depth strata separated by 2 to 5 m. The samples were divided into five size-classes: > 1000 μm. 500–1000 μm, 250–500 μm. 125–250 μm, 60-125 μm, During spring and autumn there were maxima in the total biomass. about four times higher than during summer. At the time of biomass maxima, the total biomass showed a bimodal vertical distribution, with maxima in the upper and the lower part of the water column. The upper maximum was located between the surface and the base of the thermocline, the lower in the oxycline. During summer, when the total biomass was low. the vertical pattern diminished. The same trends were observed in 1983 in all size-classes, except for the > 1000-μm size-class. This size-class had a single biomass maximum during summer, located in the upper part of the water column. Seasonal variation in vertical distribution and in depth-integrated biomass increased from the smaller towards the larger size-classes. Relations between the vertical distribution of zooplankton biomass and other biotic and abiotic factors are discussed.