Ammonium release by juveniles and adult females of the subtropical marine copepod Eucalanus pileatus

Release rates of ammonium by nauplii, copepodid stages (CIIand CIV) and adult females of the marine copepod Eucalanus pileatusat 0.1 and 3.0 mm³ 1^–1 of the diatom Thalassiosira weissflogiiwere determined at 20°C. When food was abundant, animalsof all stages released ammonium at similar rates per unit ash-freedry weight 24–35 nmol NH₄(mg AFDW)^–1 h^–1on average]. At low food levels, CIVs and adult females releasedammonium significantly more slowly than did the naupliior CIIs28 and 24 versus 51 and 50 nmoles(mg AFDW)^–1h^–1].Because they weighed less (50%), low-food nauplii and CIIs hadhigher calculated weight-specific excretion rates, than high-foodones of the same stage but release rates per copepod were similarin the two food regimens. In contrast to the early life stages,the CIVs and adult females released less ammonium per copepodin the low-food than in the high-food environment. ¹GLERL - Contribution No. 380