Nutrient Regeneration by the Larger Net Zooplankton in the Southern Basin of Kaneohe Bay, Oahu, Hawaiian Islands

Abstract

Four experiments were performed during February 1974 with
\nmixed zooplankton collected with .33-mm mesh in the southern basin of Kaneohe
\nBay. The mean specific excretion rates multiplied by the estimated average
\nstanding stocks of the animals gave estimates of addition to the bay waters of
\nammonia, phosphate, dissolved organic nitrogen, and dissolved organic phosphorus
\nof 38.6,4.0,23.7, and 3.2 ng-at/liter/day, respectively. The specific excretion rates
\nwere not significantly affected by the concentrations of animals in experimental
\nvessels, by the estimated concentrations of food in the environment on the days
\nof the experiments, nor by incubation periods of up to 4.5 hours.
\nThe rates are comparable to those obtained from zooplankton of this general
\nsize in environments that have rather different temperature and food levels, indicating
\nthat size-dependent metabolic rates are the major determinant of specific
\nexcretion rates, although feeding and temperature can affect the results of
\nexperiments.
\nTwo collecting devices, a conical net and a purse seine made of the same
\nplankton mesh, were used to assess possible effects of capture on the results. The
\nanimals from the net hauls excreted phosphate more slowly and dissolved organic
\nnitrogen more rapidly than did those from the seine catches, possibly as a result of
\nthe greater initial crowding of animals in the cod-end jar of the towed net. There
\nwas no evidence that animals were damaged by collection and no observable
\neffect of initial shock.
\nAlthough principally carnivorous, the animals in these experiments (60 to
\n70 percent Sagitta) processed dietary nitrogen and phosphorus in a way similar
\nto that of the mainly herbivorous Calanus: they constructed body tissue that was
\nricher in nitrogen relative to phosphorus than was their food and they excreted
\nsolutes that were relatively poorer in nitrogen than was their food.