Algal Culture Techniques
Different volumes of algae are grown at the hatchery for different purposes. Small scale stock cultures are grown to provide a supply of starter cultures to inoculate larger volumes of water. Intermediate size cultures are grown to inoculate the large scale cultures. The large scale cultures are then used to feed the oyster larvae. When growing algae for the hatchery, cultures at all scales require sterile water, f/2 nutrient media, light, air, and CO2.
Stock cultures are small monospecific cultures started with small cultures that have been obtained from culture collections at reputable institutions. The hatchery has two sizes of stock cultures- 125mL and 500mL. The 125 mL flasks are only used to inoculate new stock cultures every three weeks. The larger 500 mL stock cultures are used to inoculate the intermediate scale of cultures. Since these cultures are used to start all other levels of cultures, they need to be kept sterile and the risk of contamination needs to be minimized.
Carboys are larger cultures used to inoculate the mass algal tanks. Our hatchery uses 20 liter glass containers.
In our greenhouse, 18- 5000L mass algal tanks are used to provide large scale cultures that can be used to feed the oysters, primarily larvae. After being inoculated with several carboys, the algae blooms for approximately 4-6 days. Densities may reach 1-4 million cells/mL. These large scale cultures can be batch cultures or semi-continuous cultures. Batch cultures are completely harvested. Once the tank is drained, it can be sterilized and inoculated with a new culture. Semi-continuous cultures are only partially harvested before being refilled with sterile water and nutrient media and the same culture is allowed to rebloom.
In order to produce high density cultures, new technologies have been implemented including Solatubes and a new pH sensor system. Solatubes allow light to be concentrated and directed to each of the mass algal tanks and help the cells get sunlight even on overcast days. The pH sensors are a part of an accurate feedback system that allows the computer to direct carbon dioxide into the algae cultures in order to help control the pH among other factors.