Respiration and nitrogen excretion by some marine zooplankton in relation to their life cycles

Rates of respiration and nitrogen excretion have been measured for freshly caughtCalanus finmarchicus(Gunnerus),Calanus hyperboreus(Krayer),Metridia longa(Lubbock) andPareuchaeta norvegica(Boeck), from the Gulf of Maine at all seasons. The dry weight, total (Kjeldahl) nitrogen, and fat were also determined for the same animals. Seasonal variation in weight-corrected respiration and nitrogen excretion followed a similar pattern for all four species, being high in the spring and decreasing gradually through summer and fall to a winter minimum. However, the relative proportions of oxygen utilized to nitrogen excreted were different from season to season for each species. InCalanusspp., O: N ratios by atoms were highest in May, immediately after the spring bloom of phytoplankton, when the animals were rich in fat. WithC. hyperboreusthe ratio then declined gradually through summer and fall to a low point just before the spring bloom (March and April) when populations contained the least amount of fat; but withC. finmarchicusthe ratio fell much more rapidly, remaining near 17 through summer and fall and increasing again with the production of the overwintering generation. InMetridia and Pareuchaetathe O:N ratios did not show as much seasonal variation, although there was a pronounced increase for Metridia just after the spring bloom. Both species usually had higher respiration and excretion rates and lower O:N ratios compared with Calanus spp.