GROWTH AND ENERGY ALLOCATION IN THE DEEP-SEA URCHIN ECHINUS-AFFINIS

Growth of regular echinoids, expressed as lest diameter through time, generally shows a sigmoidal pattern. However, when urchin size is cons idered in terms of test volume we show growth of the deep-sea echinoid Echinus affinis is ultimately linear, rather than saturating. We cons truct a simple allometric model of energy allocation that produces lin ear growth in volume in mature urchins by allocating an increasing pro portion of net assimilate to reproduction. This model provides an exce llent fit to the observed growth curve data. Data on gonad weight as a function of test diameter allow us to test the relationship between a llocation to reproduction and urchin size predicted from the growth cu rve fit. Simultaneous fitting of the growth curve and gonad weight dat a allow us to consider a model where the allometry of net assimilation is allowed to vary. We investigate possible explanations for the fact that net assimilation appears to rise faster than linearly with weigh t in E. affinis. We conclude that strategic models of individual energ etics provide a useful tool for the analysis of the limited data avail able on deep-sea populations.