Feeding, Growth, Reproduction and Nitrogen Utilization by the Harpacticoid Copepod, Tigriopus Brevicornis

Abstract
Growth of the littoral harpacticoid copepod Tigriopus brevicornis O. F. Müller was measured in an intertidal rock pool. The generation time at the field temperature of 15°C was 31 days, and growth during this period resulted in an increase of 1.1829 μg body nitrogen.Measurements of nitrogen excreted by developmental stages were made on animals removed from the natural population. Ammonia comprised on average 89.7% of the total nitrogen excreted by adults. Some measurements of phosphorus excretion indicated a nitrogen: phosphorus ratio in excretory products of 4.86. Adult females excreted 27.2 μg N/mg dry wt/day, representing a release of about 30% of body nitrogen daily. Excretory rates of earlier copepodite and naupliar stages were higher.The efficiency with which ingested food was assimilated was measured for animals feeding on natural suspended matter obtained from the pool. Assimilation efficiencies averaged 75.4%.Egg production was measured at a range of temperatures in the laboratory, enabling an estimate to be made of total production by an individual female. At 15°C females produced an average of ten egg sacs in 30 days.Measurement of nitrogen lost during moulting suggested a value of 6% of total body nitrogen.The data obtained have been used to estimate growth efficiency in terms of nitrogen during the entire life-history of a female in the pool. Gross growth efficiency calculated for the period of growth from egg to adult is 13.0% and the net efficiency 17.2%. Efficiencies of egg production by the adult female are higher, the gross efficiency being 22.1% and the net 29.3%. During the entire life-span 72.9% of assimilated nitrogen is expended in metabolism, 3.9% in growth, 0.4% as moults, and 26.6% in egg production.