Ammonia excretion rate of Clytia spp. hydromedusae (Cnidaria, Thecata): effects of individual dry weight, temperature and food availability

Abstract

Ammonia excretion rates were measured for a variety of individual weights at 15, 18, 21 and 25°C using four food concentrations (7, 15, 25, and 50 copepods 1-1). Excretion rate increased with medusa dry wt and was directly correlated with temperature and food availability. Excretion values ranged btween 0.04-0.936 μg-at.N-NH4 mg-1 d-1. The daily nitrogen turnover (only considering ammonia) ranged from 6% at the lowest temperature and food concentration to 33% at 21°C and the highest food concentration. Calculation of the growth budget, which represents the difference between quantity of nitrogen in food ingested and nitrogen lost through ammonia excetion extrapolated to the natural environment, showed high values during the spring, up to 55 μg N d-1 ind.-1, and slightly negative values during the rest of the year. -from Author