Short communication. Carbon:nitrogen ratios of Baltic Sea copepods-indication of mineral limitation?

Abstract

The carbon (C) and nitrogen (N) content and the C:N ratio of two common calanoid copepods, Eurytemora affinis and Acartia bifilosa, were measured during spring and summer at the SW coast of Finland, northern Baltic Sea. The C:N ratio of both copepod species was low and stable (4-4.5), irrespective of sampling time, which implies N limitation at least during intermediate to high food concentrations in spring and early summer. In addition, experiments were conducted to reveal whether the diet of copepods affects their C and N content. Adding green algae Brachiomonas submarina in concentrations of 50-500 µg C l-1 to <100-µm-filtered sea water did not significantly increase copepod C or N content in 3 day experiments. However, the C and N contents of E.affinis eggs were ~2 times higher in high food concentration, which may increase survival of eggs and nauplii. The production of freshwater zooplankton is frequently shown to be limited by