EVIDENCE OF A CHEMICALLY MEDIATED ADULT LARVAL INTERACTION TRIGGERING SETTLEMENT IN OSTREA-PUELCHANA - APPLICATIONS IN HATCHERY PRODUCTION

A broodstock of flat oysters, Ostrea puelchana, was collected in natural grounds from San Matias Gulf (Argentina: 41 degrees 63'S) and transported to France with the purpose of rearing larvae in a hatchery and growing juveniles in a nursery. The parental stock was conditioned for maturation, spawning was induced, and larvae were cultured in tanks. Larval planktonic life lasted from 17 days (23-25 degrees C) to 20 days (19-20 degrees C). Settlement rates, estimated on nylon film, ranged from 50 to 70%; estimates from spat survival on the sieves were 38 to 98%. The rate of settlement increased when water from the tanks containing the parental stock was added to the sieves, confirming the existence in this species of a chemically mediated adult-larval interaction. This was further investigated on the natural oyster grounds in Argentina. The spatial pattern of recruitment on natural substrata, studied during a settlement season, shows that larvae settle on all the hard surfaces, but preferentially on the shells of living oysters. The number of recruits settled during the settlement peak was significantly higher on living oysters than on dead oysters. Density of recruits on living oysters decreased as shell surface increased, while no such trend was apparent in the case of dead oyster shells. This pattern suggests that the total number of larvae attracted by each oyster is independent of its size. Elucidation of the chemical nature of the attractant would be of interect due to its potential importance in commercial oyster hatchery production.