Collected reprints: Abstract 3406
De Pauw, N. (1981). Use and production of microalgae as food for nursery bivalves. Europ. Maricult. Soc. Spec. Publ. 7: 35-69
The nutritional value of various foods and diets for juvenile bivalves is reviewed and commented. From all foods tested specific microalgues seem to be the most suited for young bivalves. Presently, serious alternatives for replacing living algae by inert, artificial feeds are practically inexistent, though research efforts are made in this direction.
The various microalgae production system used for feeding juvenile bivalves are also reviewed.
A literature survey and the cost inquiry held in 1979 by our laboratory revealed that nearly all commercial enterprises involved in nursery rearing of bivalve molluscs in Europe utilize natural phytoplankton as food. Culturing of the postlarvae is performed eitherin situ (in the sea) or in onshore constructions with flow through pumping of seawater.
In contrast to these technologies, small-scale as well as large-scale experiments carried out in many countries, have shown the potential and reliability of culturing suited microalgal species for nursery bivalves, in analogy to the well established algal culturing for hatchery molluscs.
Some hatcheries continue to feed the spat with the same specific species of microalgae which are used to rear the larvae. Increasing quantities of algae needed to satisfy the growing food demand of the postlarvae soon, however, becomes a limiting technological as well as economical factor. For these reasons scaling up of the highly controlled and often sophisticated systems used to produce monospecific algae seems to be prohibitive.
To date two major trends can be distinguished for large-scale production of algae to be used in mollusc nurseries.
The first one relies on the completely controlled production of specific algal species. This implies keeping stocks of monospecific algae, progressive inoculation of cultures of increasing volumes, advanced water-treatment and controlled culturing conditions indoors (or in greenhouse).
The second trend is based on the induction of natural phytoplankton blooms in outdoor systems. This technology strives at a certain control of the species composition of the algal bloom by manipulating different internal and ambient parameters, such as nutrients, pH, detention time, and mixing.
The pros and cons of these two trends are considered in the light of economic considerations.
The biotechnical aspects of large-scale production of algae are discussed: yields and harvest regimes, modes of seawater enrichment, inoculation, collapsing and contamination of cultures, and culture systems and dimensioning of an algal plant for a bivalve nursery. The factors determining the production price of algae are analysed. The present trends and possibilities of a more controlled way to produce food for nursery bivalves are examined.
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