Physical‐Chemical Methods For Control Of Algal Species And Composition In Algal Culturing Facilities

The bivalve molluscs Crassostrea virginica and Mercenaria mercenaria require species of algal food for growth. Successful commercial culture of the hard clam and American oyster in a controlled environment depends on an ability to grow desirable species. Three methods are described for the selective culture of Thalassiosira pseudonana, a desirable bivalve food, in the presence of a contaminant species Phaeodactylum tricornutum, an undesirable food. The first method takes advantage of differences in cell wall characteristics between the two types of algae. Cultures of T. pseudonana contaminated with 34% and 60% P. tricornutum (by cell numbers) treated with ultrasonic waves yielded growing cultures of T. pseudonana which were free of P. tricornutum when 100% T. pseudonana were treated with ultrasonic waves they showed no growth and normal growth respectively. The second method involves manipulation of nutrient levels in a mixed culture of Thalassiosira pseudonana and Phaeodactylum tricornutum to eliminate one or other species from the culture. The third method utilizes a harvesting reseeding technique to maintain a relatively constant concentration of the slower growing species in a semi‐continuous mixed species culture containing Carteria chuii and Thalassiosira pseudonana. The results are integrated into a two loop algal culturing process. One loop consists of a seed culture utilizing a small percentage of the influent water and a larger mass algae culture. The mass algae loop is continuosly inoculated with new seed from the seed loop in sufficient quantities so that desirable species out compete undesirable species. Water entering the seed loop is purified by an ultrasonic treatment process so that undesirable species may be eliminated from the seed cultures.