Respiration and nitrogen excretion by some marine zooplankton in relation to their life cyclesConover, R.J. and Corner, E.D.S. (1968) Respiration and nitrogen excretion by some marine zooplankton in relation to their life cycles. Journal of the Marine Biological Association of the United Kingdom, 48 (1). pp. 49-75. Full text available as:
AbstractRates of respiration and nitrogen excretion have been measured for freshly caught Calanus finmarchicus (Gunnerus), Calanus hyperboreus (Kroyer), Metridia longa (Lubbock) and Pareuchaeta 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. In Calanus spp., 0:N ratios by atoms were highest in May, immediately after the spring bloom of phytoplankton, when the animals were rich in fat. With C. hyperboreus the 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 with C. finmarchicus the ratio fell much more rapidly, remaining near 17 through summer and fall and increasing again with the production of the overwintering generation. In Metridia and Pareuchaeta the 0: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 0:N ratios compared with Calanus spp. A simple- and multiple-regression analysis was undertaken to ascertain the effect of size on metabolism using respiration rate (R') in ul. O2 mg-1 day-1, excretion rate (E') as ug nitrogen mg-1 day-1, and 0:N ratio by atoms as dependent variables; and dry body weight (W), total nitrogen (N), and total fat (F), all in ug, as independent variables. All simple and multiple regressions were highly significant. The presence of fat had a suppressing effect on metabolism, and in its absence, the proportionally higher level of protein resulted in higher rates of both respiration and nitrogen excretion. Removing the individual correlations between metabolism and the size parameters by covariance did not remove the statistically significant difference in respiration, excretion rates, and O:N ratios between the group composed of Calanus and near relatives (herbivores) on the one hand and the Metridia-Pareuchaeta group (omnivores and carnivores) on the other. Reasons for this persistent difference are still largely unknown, but the Calanus group can store fat and regulate their metabolism against the time when conditions are less favourable for them, thus achieving a greater degree of independence from their environment than the so-called omnivore-carnivore group.
NMBL Staff Only: edit this record |
|
