Rate of natural mortality in the sea starArchaster angulatus(Echinodermata: Asteroidea)

Abstract

The population size structure from a total of 876 individuals, together with published values of growth rate, maximum size and size at age were used to estimate an instantaneous rate of natural mortality (M) of 0.46–0.59 year−1 in a population of the sea star Archaster angulatus from south-western Australia. Peak abundance (17%) of all animals sampled was 105–109 mm arm radius (means of 4.2–4.8 years of age) and only one per cent of sea stars are predicted to live beyond 8 years in the population studied. There are few comparable studies on sea stars but when compared with rates of natural mortality in other echinoderms (sea urchins), A. angulatus is intermediate among species which exhibit the extremes of life history strategies, that is, those which grow very rapidly and may live just two years or less and those with very slow growth rates and which may live for decades.