The aim of the research is to succeed in continuously producing a large amount of edible sea urchins with high gonadal productivity under controlled conditions (aquaculture). The selected species is Paracentrotus lividus (the edible echinoid species from Europe). The research will focus on the following aspects: investigation of metamorphic events with a special interest in metamorphosis inducing factors; optimization of juveniles' somatic growth and adults' gonadal productivity under rearing conditions; and the study of reproductive periodicities in field and cultivated individuals, attempting a continuous reproduction under aquaculture conditions.
A study was made of the morphological changes affecting the larvae of Paracentrotus lividus during the metamorphic period and the environmental factors that influence metamorphic initiation were examined. Investigations concerned particularly the formation of 4 specialized swimming organs (viz the epaulets) that develop from the ciliary band of echinoid larvae.
Competent larvae were induced to metamorphose when they were put in a rearing structure that includes adult conspecific and their food (Enteromorpha and Laminaria algae). The presence of juveniles or adults of P lividus as well as the foresaid algae had no inducing effect. Experiments using detritic material from the rearing structures give good rates of metamorphosis. The coralline type red algae, Corallina elongata and Litophyllum incrustans give the best rates of metamorphosis.

The effects of 3 kinds of food on the survival of early juveniles was investigated. Enteromorpha species gave by far the best results.
The feeding rate, the rate of absorption of the ingested food and the somatic growth of 12 to 35 mm juveniles were measured using fresh Laminaria digitata as only food. The absorption rate stayed the same, 70 to 77% in dry weight, if the animals were fed every 1, 2 or 3 days. Results for absorption rate did not vary under different photoperiod conditions.

Observations showed that the outline of the gonads appeared in 4 mm individuals. The genital apparatus was clearly distinguishable in 6 mm individuals and gonads started filling up in 8 mm individuals. Another investigation on larger juveniles showed that size has much more influence on the development of the genital apparatus than age.
Paracentrotus lividus clearly has an annual reproductive cycle: it spawns in summer and gonads fill up with reserve material during the winter to start gametogenesis at the end of the winter. Temperature seems to be the parameter that triggers gametogenesis although photoperiod might also have an influence.
The project will be carried out in the following 3 phases.
Firstly, metamorphosis which is a crucial period of the sea urchin life cycle. Phase 1 will need to perform routinely mass cultivation of larvae. Research in phase 1 will focus mainly on the following aspects: the morphology of metamorphosing larvae, investigations will concern the main external and internal morphological changes affecting metamorphic larvae; and the factors that influence metamorphosis initiation.
The second phase is growth. 3 postmetamorphic growth periods can be distinguished that are the early growth (from 0.5 to 3 mm test diameter), the juvenile growth (from 3 to 40 mm test diameter), and the adult growth (beyond 40 mm test diameter).
The third phase is the cyclic aspect of reproduction. The point is to study the reproductive cycle of field, geographically distinct populations, and to identify the major environmental parameters responsible for the cycling of reproduction and the duration of the spawning period (phase 3A). The effect of experimental modifications of these parameters in aquacultural conditions will be tested in order to obtain ripe individuals all through the year (continuous reproduction) (phase 3B).