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Nitrogen regeneration by the subtropical marine copepod Eucalanus pileatus
Authors:Gardner  Wayne S; Paffenhofer  Gustav A
Institution:2National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory 2300 Washtenaw Avenue, Ann Arbor, MI 48104 3Skidaway Institute of Oceanography P.O. Box 13687, Savannah, GA 31406, USA
Abstract:Ammonium release rates by individual marine copepods (Eucalanuspileatus) were examined kinetically over successive 10-min intervalsafter the animals were exposed to three concentrations of thediatom Thalassiosira fluviatilis as food. Food concentrationsspanned those expected in the natural environment. "Well-fed"(3 mm3 T. fluviatilis l–1) copepods released ammoniumsignificantly (p<0.05) faster than those fed zero or lowconcentrations of food, but differences were not dramatic. Meanexcretion rates (± SE) for animals removed from foodfor 18 –22 h 30 ± 6 nmol NH4(mg ash free dry weight)–1h –1] were ~60% of those for "well-fed" animals 49 ±8 nmol NH4 (mg ash free dry weight)–1 h–1]. Continuedhigh release rates after extended periods without food suggestthat E. pileatus must feed frequently in nature to maintainan adequate nitrogen balance. Depending on food concentration,animals released ammonium at rates ranging from 40 to > 100%of their N ingestion rates over the previous 18–22 h.Long-term (4–6 h) kinetic excretion experiments with "well-fed"animals indicated that, on average, release rates decreasedwith time after food removal, but patterns varied among individualcopepods. In addition to ammonium release, o-phthalaldehydereactive amino acid nitrogen was occasionally released by E.pileatus in large "spurt events" lasting from 20 to 60 min. 1GLERL Contribution No. 283
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