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

The carbon (C), nitrogen (N) and phosphorus (P) contents (% of dry weight) of some crustacean 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 Pseudocalanus 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 differences 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.