I learned my mariculture based on the traditional western model. Growing larval fish, crustaceans and mollusks into juveniles is a core part of most mariculture ventures and most of them use cultured, single cell algae as part of the feeding regime. However, through the years, I have come across three alternate systems which were very impressive. First, though, what is the classic "western" system of algae culture.
"Western" Algae Culture"
One usually starts out with a sample of sea water either from the wild or from a contaminated culture which contains at least some cells of the algae species one wants to culture. This sample is serially dilluted with sterile, nutrient-spiked-sea-water and sub samples of this water are put into a large number of small glass vessels (10cc test tubes for instance). The dillution is done sufficiently so that there is an expectation that there will only be one cell of the desired species in at least some test tubes. The rack of test tubes, corked with cotton wool to allow air exchange while excluding contaminating organisms, are incubated on a light table for an appropriate length of time. Microscopic examination then determines which test tubes have been successful in growing the desired species and these samples, individually or pooled, are used to inoculate larger vessels (erlenmeyer flask for instance) Three to five stages are typically needed to bulk up the algae to a useful quantity for feeding to larval animals and in the larger cultures, Carbon dioxide enriched air is often bubbled through the culture. In a modest sized algae growing facility it is typically the full time job of one or more people to manage the algae cultures. The first alternate system I saw was a Bio-stat system.
The biostat system is closest to the classic western model. Algae are isolated and bulked up in the same way. However in the last stage, a growing vessel called a bio-stat is inoculated. A bio-stat (possibly better named a bio-dynam), is a vessel which is sealed except for two inlet ports and two outlet ports. One inlet port allows the constant in-flow of sterile (or well filtered) carbon dioxide charged air and the air is typically inserted through an air stone at the bottom of the vessel. A second inlet port allows a continual stream of nutrient charged, filtered and sterilized sea water to flow into the bio-stat. One outlet port has a "brewers trap" to allow the excess air to exit and the second outlet port lets out the overflow algae culture into a holding container or directly into the larvae culture. It can be shown mathematically, and experience supports the fact, that the maximum algae production (not the maximum concentration) occurs when the exchange rate is the same as the doubling time of the organism which is being cultured. In algae cultures, this is typically a few hours to a few days, depending on a number of environmental factors, all of which the operator endeavours to control. Bio-stats don't always work and if the "clean technique" of the operator has slipped somewhere along the line, contamination can occur and the culture crashes or takes off with the wrong organism. However once a bio-stat is up and running, it can operate for a very long time (months), producing log phase algae with a minimum of effort. Log phase refers to the sigma curve of growth and is the part of the growth curve where the algae are growing at more or less an unrestricted rate. Fast growing algae generally have the best food value and freedom from toxins. They are the "tender young peas" of the mariculture trade, rather than the old woody carrots. Besides being great production vessels, bio-stats are excellent for research. Very subtle changes can be made in the inlet parameters such as temperature, light, nutrient mix and so forth and the results easily monitored, even automatically, with something like a spectrophotometer set to the wave length of chlorophyll absorption. Of course much more elaborate observations can be made from microscopy to sedimentation volume through to chemical composition .
The best example I have seen of this system was at Seasalter Oyster Hatchery in Kent in England. John Bayes was the manager and he had bio-stats consisting of plastic sleeves of about 3m circumference and 2m high. As I remember, there were about ten of these in his light room and he had banks of fluorescent tubes immersed in the bio-stats to increase the light availability. The sleeves were supported by cylinders of wire weld mesh with about a 2" hole size. Amazingly, he could insert a needle into the plastic for the removal of a sample or the introduction of more air without the sleeves splitting. At the bottom he would pour a cylindrical vessel of the same diameter as the sleeve, full of runny concrete, put the bio-stat in place and fill it with water. The concrete then hardened with the shape of the bottom of the bio-stat and from then on, perfectly supported it. As far as I remember, John and his assistant, Rayner, ran the whole hatchery by themselves, including the algae culture and all the other units that made up the operation. The next method that impressed me was the "Chesapeak Bay" system.
Chesapeak Bay System
This system was used in the Eastern Shore laboratory of The Virginia Institute of Marine Science. Mike Castagna ran the unit and when I visited, many many years ago, he had successfully raised the larvae of well over a hundred different mollusks (including the Indian Wampum, otherwise known as the jingle shell) Mikes system was pure elegance in the sense that a mathematician or a physicist talks about elegance. In other words, a system that solves a problem with less steps than has hitherto being discovered. Mike took sea water straight from the ocean and pumped it into open tanks. The water was first filtered to eliminate large algal species and to mainly let through small diatoms. Standard nutrients were added, making sure to include sodium silicate for the diatoms.
The open tanks were located on a balcony around the top of the laboratory just under the roof and the roof was translucent. It was probably fibreglass. At that time, I don't think polycarbonate was available. I seem to remember that he bubbled air into the tanks but I don't think he even enriched with Carbon Dioxide. I suppose for the short blooming he used there was enough carbonate in the water and the introduced air. The water was only allowed to 'grow' for a day or two before it was used and if you looked through the tanks they showed a sort of milky cloudiness. They hadn't even turned green yet. Talk about tender young peas. Mike probably raised more different species of mollusks with this system than anyone else has even tried. The third impressive system was one I saw in a Thailand prawn farm.
The Eastern Prawn Algae System
The algae grown in this system is the chain diatom Sleletonema sp. which fortunately, larval prawns take to at an early age. Under the microscope one can occasionally see a larval prawn riding a strand of algae like a lion on a buffalo and eating it from one end. The critical fact that allows this type of culture is that the skeletonema can be filtered from a water stream by what can only be described as a pillow case. Pillow cases of the correct material are available at all hatchery supply stores in the East. This sort of culture is carried out in open tanks of about 2 to 5 cubic meters, sometimes in a special room with a translucent roof on the sunny side of the hatchery. I saw one hatchery, though, with the tanks under the open sky outdoors. The usual algae culture nutrients including sodium silicate are used and in Thailand it is common to filter the incoming water through a sand filter. Tanks are typically painted blue or white inside. Enough aeration is supplied to keep the water moving. For innoculation, a "pillow case" is tied with a string around the end of the outflow pipe of a previous successful culture and the outflow pipe (on the outside of the tank) is lowered to the ground and allowed to flow for 5 or 10 minutes. The pipe is hitched back up and the pillow case removed. Inside will be a thick soup of skeletonema. The algae is resuspended in a bucket of water and either fed to the prawn larval tanks or used to start a new culture. Typically, each culture must be renewed at the most after 2 days as the growth is so fast. Three day cultures are usually over the hill. The filtration of the incoming water through a sand filter is mainly to remove animal larvae which are not wanted in the prawn culture. Sand filters are typically the size of small swimming pools and produce sparkling clear water from the very opaque water of the gulf of Siam.
The filtering through the pillow cases continually cleans the culture. There are always other diatoms and some other algae growing in these cultures but the innoculation of each new culture is massive and the other algae selectively pass through the pillow cases so every transfer is a re-cleaning of the culture. I imagine that another chain diatom such as Chaetoceros might cause problems with this sort of culture but I never observed a problem. In a prawn farm I ran, the running of 6 such tanks was the work of at most, half an hour a day and there was always an abundance of algae available.
You musn't think I am knocking the western system. It is a great research tool, especially if your interest is in, for instance, finding out the nutritive quality of a particular species of algae. However for a working mariculture system, cost is often important and a system which eliminates one or more full time jobs can be critical. Even if these systems occasionally fail, the success over most of the time more than makes up for the occasional glitch. I think, sometimes, the problem is that we westerners are control-freaks. We want to have absolute control of everything that happens. We may, for instance, in our homes, eschew pure solar water heating for electrical heating since we aren't willing ever to be without hot water. It may be the same with algae culture. We may not be willing to operate a little closer to nature when we have been used to having complete control. I suspect, with the need for sustainability, a philosophical shift may be necessary in the west. I know that since we put solar water heating on our roof, we have become a little more conscious of the weather outside. A small step but perhaps the first of many. In the case of algae culture, the above systems were so successful that they gave their practitioners quite and advantage.