Inorganic nitrogen uptake and regeneration in perennially icecovered Lakes Fryxell and Vanda, Antarctica

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Abstract
The population dynamics of the euphausiids Thysanoessa inermis (Kröyer), T. raschii (M.Sars), and Meganyctiphanes norvegica (M.Sars) have been followed in Balsfjorden in 1976 and 1977. Seasonal variations in length-frequency distributions, growth in carapace length, sex-ratio, and spermatophore production and attachment are presented and discussed in relation to changes in hydrography and phytoplanlcton standing-crop. An annual generation of T. inermis and T. raschii was spawned in April and May. Eggs and larvae of M. norvegica were not found in Balsfjorden, indicating that recruitment occurs from outside the fjord. T. inermis and T. raschii reached maximum carapace lengths of 7–8 mm and 6–7 mm respectively and had life-spans of c. 2 years 3 months. M. norvegica had a life-span of c. 2 years 6 months and reached a maximum carapace length of c. 12.5 mm. In both T. inermis and T. raschii 0-group underwent the greatest length increases from May to October, I-group from March to August and II-group from April to June. The population structure, growth patterns and growth periods of M. norvegica were difficult to discern. The phytoplanlcton cycle appears to be the dominant factor regulating both growth and spawning of the Thysanoessa spp in Balsfjorden, while temperature has no obvious influence.

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