Yields, photosynthetic efficiencies and proximate composition of dense marine microalgal cultures. I. Introduction and Phaeodactylum tricornutum experiments

Marine microalgae may be grown in dense, coastal pond cultures as a source of biomass energy and/or protein. Seawater, containing some elements that are used by algae, would be a useful resource. This paper, describes laboratory experiments with Phaeodactylum tricornutum toward realizing the above concept. Highest cell yields (22 g m^-1 day^-1) were achieved in batch cultures at light intensities of 40-60% of daily sunlight recorded at La Jolla, California. Thirteen per cent of the energy of photosynthetically active radiation (PAR) was converted into cellular calories. Yields and efficiencies were reduced in continuous culture and at higher light intensities. The latter effect was probably due to photoinhibition. Nitrogen-sufficient cells contained 55% protein, 10% carbohydrate, 20% lipid, 12% ash and 4·8 calories mg^-1 dry weight. Nitrogen deficiency changed these values to 25%, 15%, 22%, 16% and 5·0, respectively. During extreme deficiency, lipid content was as high as 30% of the dry weight, but lipid yield did not increase because overall cellular yield was decreased. These experiments were generally run with a CuSO₄ filter to remove infrared light energy; when the filter was removed, yields increased.