Large-scale microalgae production for nursery rearing of marine bivalves

The feasibility of large-scale bloom induction of nutritionally suited natural phytoplankton species, to feed a semi-industrial nursery of edible shellfish, built on the Belgian coast, was tested.The outdoor microalgal production unit consisted of four tanks of 100 m² surface each (two of 1 m depth and two of 0·5 m depth), equipped with different mixing devices.The cultures were run as chemostats in which seawater was enriched with commercial inorganic N, P, and Si fertilizers. Depending on the season, between 5–10 and 80% of the culture volume could be harvested daily, with algal densities ranging from 50 000 to 500 000 cells per ml.By manipulation of operational parameters such as detention time, nutrient levels and nutrient ratios (N:Si:P), unsuited or less suited species of algae (e.g. Chlorella and Phaeodactylum) could be replaced by more desirable species (e.g. Skeletonema, Nitzschia, Chaetoceros).Various biological and technological problems encountered during year round operation, including collapsing of the culture, seawater enrichment, water quality, fouling and water treatment, are commented.