Carbon, nitrogen and phosphorus stoichiometry of crustacean zooplankton in the Baltic Sea: implications for nutrient recycling

Abstract. The carbon (C), nitrogen (N) and phosphorus (P) contents ( % of dry weight) of some crust-acean zooplankton were studied in the Baltic Sea. The copepod Acartia sp. had a stable C and N content (48.3 ± 0.8 % C, 12.4 ± 0.2 % N, C:N ratio 4.5 ± 0.1). The P content was variable (1–2%), probably depending on developmental stage and season. Copepods accumulating fat, like Pseudo-calanus minutus elongatus, had higher and more variable C content (50–60%), and lower N and P content (7–12 % N, 0.6–1.5 % P). The highest C and lowest N and P contents were found in adult Limnocalanus macrurus. However, the N:P ratio was apparently independent of fat content and between 14 and 27 for all copepods. The cladocerans Bosmina longispina maritima and Evadne nordmanni had lower N content (9.3–10.8%) and higher C:N ratio (5.1–5.7) than Acartia sp. The P content (1.2–1.4%) was similar to Acartia sp. and the N:P ratios (16–19) were in the lower range of that found for the copepods. The N:P ratio was generally somewhat higher in the copepods than in seston, which most of the year had nearly Redfield C:N:P ratios. Potentially, nutrient recycling from crustacean zooplankton could enhance N limitation of phytoplankton, but small stoichiometric differ-ences suggest that this effect is probably weak. The extent is dependent on the structure of the zooplankton community and the gross growth efficiencies. Acartia copepodites, which had nearly Redfield N:P ratios, would have the opposite effect and enhance P limitation in late summer when seston N:P ratios increased