Life cycle and spatial distribution of the amphipod Pallasea quadrispinosa in a lake in northern Sweden

The population structure and spatial distribution of the "glacial relict" Pallasea quadrispinosa were studied in Lake Stora "Ofsjön". Samples were taken at three depths throughout an eleven month period. The amphipods had an annual-biennial life cycle. The reproductive period started in October, and hatchlings were released from November until July. Four cohorts were present in November. Some one-year-old females appeared to reproduce more than once. Ontogenetic niche segregation occurred from June to September, when juveniles were found in shallow water and adults were found in deep water where temperatures were below 10°C. The diet included phytoplankton, zooplankton and chironomid larvae. The amphipods were infested by several parasites, including larvae of Cystidicola sp., a swimbladder nematode that infects fish.