Variation in the reproductive strategy of the sea urchin <i>Sphaerechinus granularis</i> (Echinodermata: Echinoidea) related to food availability

Abstract

Changes in the reproductive strategy of Sphaerechinus granularis (Echinodermata: Echinoidea) according to food availability were examined by comparing gonadal index changes from two populations with different food conditions. The better nutritional situation was confirmed by a repletion index always higher without significant inverse relationships with the gonadal index. The two populations exhibited a different reproductive strategy during their life cycle. The food limited population showed a delay in reproductive competence, a lower gonadal index and an increase in relative gonadal growth with age. This population showed a seasonal inverse relationship between the consumption index and the gonadal index during the spawning period. A discussion based on the variations in the main life history parameters between the two populations: reproduction, somatic growth, longevity, underlines the plasticity of this species which must maximize its reproductive output in terms of changes in food availability. The adaptive value of this plasticity was observed by the reduction in somatic growth which decreases the energetic cost of maintenance and by the increase in size of the feeding structure (Aristotle's lantern) which improves food acquisition.