Outdoor mass production of marine microalgae for nursery culturing of bivalve molluscs

Nursery rearing of bivalve molluscs as the intermediate step between the controlled production of larvae in hatcheries and non-controlled growing-out in the wild, is a practice in modern shellfishery management which receives more and more attention. A major bottle-neck in the culturing process of the postlarval bivalves is, however, the production of large quantities of marine microalgae suitable as food for the growing spat. Experience was gained by the authors in small 1 m2 outdoor units with induced blooms of natural phytoplankton. The cultures were run either as a turbidostat or as a chemostat with discontinuous or continuous harvesting.Natural seawater (25-32°) was enriched with inorganic (commercial), or organic fertilizers (manure), solely or in combination. The influence of environmental factors such as light, temperature, detention time, nutrients and turbulence on yield and species composition are reviewed briefly. As a next step, a semi-industrial pilot plant for the controlled nursery growing of edible shellfish was designed and built at the Belgian coast. This pilot-scale plant should provide bio-technical guidelines, and aims at assessing the cost-benefit of an industrial bivalve nursery