Moulting and growth in serolid isopods

Populations of Serolis polita Pfeffer and S. cornuta Studer were studied over a continuous period of 2 yr at Signy Island, South Orkney Islands. Moult classes were recognized by a combination of morphology and size-frequency analysis and the method is described. The size of moult classes was very stable for S. polita but showed marked annual variation in S. cornuta. The moulting regimes of six other species of Serolis are discussed. An assessment was made of the losses associated with ecdysis and it was found that ≈25% of the dry weight and 42% of the ash content was lost at each moult. The seasonal breeding regime allowed the recognition of cohorts in the population and the growth rate was determined. In S. polita, growth in winter was significantly slower than in summer, and this is considered to be due to reduced food availability. The growth of Antarctic species of Serolis is compared with that of temperate isopods, and it is found that the former tend to show larger body size, slower growth, and greater longevity. All three features are discussed as symptoms of adaptation to the polar environment.

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