Aspects of the ecology of the Antarctic polychaete Scoloplos marginatus mcleani (Renham, 1921); family orbiniidae.

The ecology and life history of the burrowing polychaete Scoloplos magginatus meleani were studied at two stations in Borge Bay, Signy Island (South Orkneys, B.A.T.) during 1969-72. S.m. meleani females spawned once annually, probably laying a single cocoon each during a three-six week period around midwinter. Mean fecundity was lower than in a comparable temperate species, S. Arriger. Larval development took 26 weeks, 10 spent in cocoons and the remaining 16 in the substrate. Metamorphosis was thus delayed until midsummer when the food supply was best. Ovary development began at age two years. Ovum maturation was protracted, taking two years, thus females first spawned at age four years. Females probably spawned more than once, preparing for three spawnings concurrently. In comparison with S. arajger and other polychaetes S.M. mcleani had a prolonged breeding cycle. This is a common feature of Antarctic invertebrates, that has been linked to the single brief annual plant growth period. The populations at the two stations differed in density, fecundity and individual body size. At Small Rock the mean body segment number of the adults was 163.0 and the mean preserved wet weight was 403.9 mg. Density was 661.8 ova/female in 1970 and 479.8 ova/female in 1972. At Factory Cove adults had 176.5 body segments (mean) and the mean weight was 1086.3 mg. Density was 136.5 individuals/m2 early in 1971. A model is proposed to explain changes in the populations. It is suggested that the dense population at Small Rock was close to the carrying capacity of the substrate and responded rapidly to a food shortage in 1971. The response of the Factory Cove population was delayed.