Large-scale and long-term variations in the zooplankton community of the Gullmar fjord, Sweden, in relation to advective processes

Since 1978, long-term variations in zooplankton biomass have been studied in relation to the hydrography of the Gullmar fjord, west coast of Sweden. The effects of water exchange processes on the zooplankton community were given special attention. During each autumn extremely variable numbers of Calanusspp. (Stages CIV to V) were transported to the fjord by inflows of Skagerrak surface water Once inside the fjord, Calanus spp. descended into the deep water, but were more or less completely washed out again by the annual renewal of deep water during winter or spring. An anomaly in the zooplankton biomass which was observed in 1982-84 was caused by a more than 10-fold increase in the abundance of Calanus. It was concluded that advective processes were the major factor regulating zooplankton biomass in the fjord.