3.4 LARGE-SCALE CULTURE

Commercial bivalve hatcheries need to produce large volumes of good quality, high-food-value algae daily to support economic-scale seed production. Examples of some of the systems currently in use in Europe and North America are described in this section.

They range from simple polyethylene bags either suspended, or supported by a cylinder of plastic coated or galvanized steel mesh, to

Figure 22: Large-scale culture was often in large, circular or rectangular tanks with overhead illumination. This format has been largely superceded by the use of tall, cylindrical vessels.

sophisticated electronically operated turbidostats. All have the common feature that the culture is contained in a tall, narrow cylinder, this being the most efficient configuration. Culture in rectangular (Figure 22) or circular tanks with overhead illumination is largely obsolete. The exception is in hatcheries, mainly on the west coast of North America. They continue to use large, circular tanks illuminated by high output, metal halide lamps. Highest productivity is achieved by mounting the illuminating lamps internally in the cultures (Figure 23) rather than externally as a bank of fluorescent lamps.

Figure 23: Efficient 200 l volume, water cooled, internally illuminated algal culture tanks. A – harvesting a culture by siphon.
B – details of construction. The outer fibre glass jacket has cooling tubes moulded to the outer surface to help dissipate the heat from the internally mounted fluorescent lamps. C – details of the lid of the vessels with its stoppered media inlet; cotton wool packed air exhaust at the back; an access /observation port and showing the top of the inner acrylic cylinder. The cables of the 6, 150 cm length fluorescent lamps are routed through a central, PVC core tube which also supports the clamps that hold the lamps in place.