[en] Among the technological choices to develop aquaculture of new species, open-sea versus 'on- land' cultivation is a determinant one. On-land based systems are more expensive but offer the possibility to control the environmental conditions possibly leading to better performances. In the case of echinoderms, ecophysiological responses are insufficiently understood to decide at the present time which is the best strategy. To investigate this crucial question, one should (1) set up a good cultivation system, (2) develop an experimental methodology adapted to the specificity of echinoderm biology and (3) quantify the responses of the animals against gradients of environmental parameters. As an illustration of the promising perspectives this approach offers, the case of Paracentrotus lividus is discussed.
A pilot system has been set up to control all life stages of reared sea-urchins, from fertilization to gonad filling ; the used protocol is being carefully standardized.
A rapid (3 weeks) but accurate method has been developed to measure feeding, digestion, and somatic growth of reared sea-urchins under various environmental conditions. Both technical and statistical improvements have been made to increase the significance of the results.
Two of the most important abiotic factors (photoperiod and temperature) have been investigated and let us to modelize their effects on sea-urchins. Photoperiod has an impact on the feeding rate, but not on absorption or somatic growth. Optimal temperature for juveniles appears to be higher than for adults (respectively 23-24°C and 19°C). Moreover, juveniles are more sensitive to departure from this optimum. Hence, a strict control of temperature is a more critical issue for juveniles, than for adults.
Integration of our results in a wider model concerning the entire rearing structure shows that the apparent food conversion efficiency results in several complex phenomena : feeding and digestion of course, but also the degradation of food that in addition depends on temperature. In cultivation, the highest productivity is obtained by making a compromise between a high somatic growth at optimal temperature and a high apparent food conversion efficiency at a lower temperature.
