Modification of the nutritive value of Phaeodactylum tricornutum for Artemia sp. in semicontinuous cultures

The biochemical composition of the marine microalga Phaeodactylum tricornutum was modified through semicontinuous culture techniques. Six concentrations of nutrients were combined with six renewal rates to generate 36 different microalgal cultures. The nutritive quality of these cultures was tested by measuring survival, growth and production of nauplii by Artemia sp. There was a wide range of responses generated in Artemia after 23 days of culture, with survival ranging between 17 and 97%, length ranging between 7 and 10 mm, and from 3 to 97 nauplii per spawning, demonstrating that culture conditions can cause dramatic differences in the nutritive value of a microalgal species. Growth, survival and production of nauplii were directly related to growth rate and nutrient concentration in the microalgal culture in the range 0.5–8 mmol N l −1 and renewal rates 10–50%. Microalgal protein content or protein/lipid and protein/carbohydrate ratios could not explain all the differences in the nutritive value of the microalgae. The production of nauplii per spawning was the most sensitive parameter for evaluating the nutritional quality of the microalgae. Results demonstrated that semicontinuous cultures of microalgae provided a simple and useful tool for the study of nutritional requirements of filter-feeding organisms and to manipulate the growth of Artemia nauplii.