Sequences in Metabolic Rates and Elemental Composition (C, N, P) During the Development of Euphausia Superba Dana and Estimated Food Requirements During Its Life Span

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Abstract
Some general trends over the life history of Euphausia superba in the rates of metabolic activities (O2 uptake, ammonia excretion, phosphate excretion) and in the elemental composition (C, N, P) are presented. The O2 uptake rate of the eggs is low (about 0.1 μl O2 mg dry wt–1 h–1), rising to a maximum in the calyptopis stage (1-2 μl O2 mg dry wt–1 h–1), then decreasing gradually as development proceeds towards mature adults. Phosphate excretion rates tend to decrease from the calyptopes to the mature adults, while ammonia excretion rates are rather constant throughout these developmental stages. Although no excretion measurements were made on the eggs and nauplii, the rates are thought to be low since these stages do not feed. The high C content of the eggs (55% of dry weight) has dropped markedly by the calyptopis (33%) but then rises gradually with development towards the mature adult (48%). The N content is rather stable throughout the development from eggs to mature adults (9–11%). The eggs contain a low content of P (0.5%), but P reaches its maximum value at the calyptopis stage (1.4%). The P content declines in the development from calyptopes to mature adults (0.7%). The total food requirement of E. superba during its life in the Southern Ocean is estimated by combining the metabolic data with the growth scheme proposed by Mauchline (1980) ("M-scheme"). With the M-scheme, E. superba having annual growth periods of 180, 150, and 120 days require 2,259 mg C, 2,102 mg C, and 2,848 mg C, respectively. This M-scheme assumes continued feeding during the Antarctic winter, with little growth and no moulting. An alternative scheme is proposed with regular moulting occurring over winter (despite the complete cessation of feeding) leading to a gradual shrinkage of body size ("MS-scheme"). In this scheme, the food requirements of E. superba with annual growth periods of 180, 150, and 120 days are reduced to 1,554 mg C, 1,532 mg C, and 1,703 mg C, respectively. The overall gross growth efficiency is 9–12% in the M-scheme and 15-17% in the MS-scheme.

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