There is a clear trend all over the world to shift from the harvesting of natural resources to various mariculture systems (Michanek, 1978). In many cases, the reason has been overharvesting and extinguishing of the natural resources, e.g., of Eucheuma in the Philippines. This may become the consequence of free access to the marine algae.
There are two more reasons in favour of cultivation rather than owning the crop: suitable substrates may be lacking (as along most of China's coast) or the natural crops are too contaminated with epiphytes and other competing species (e.g., Porphyra in Japan).
These arguments hardly apply to Chile. Gracilaria grows on (and partially in) soft bottoms, where it has very few competitors and many of the large beds are in brackish water, which reduces competition to practically zero.
However, Gracilaria cultivation is tried in many parts of the world, sometimes as a method to utilize the nutrients of sewage treatment plants, water from which is added in 10–25 percent to natural sea water. A survey of cultivation basin size and water exchange rate is of an interest as it shows how different cultivation methods influence production:
| Method | g·m-2 ·day-1 | t·ha-1 ·yr-1 | Exchange rate volume·day-1 | |
| mean value | range | |||
| Dams, Taiwan | 2.7 | 10 | 0.3–0.5 | |
| Indian River | 2.5 | 0–10 | 9 | unknown |
| 20 000-1 dams | 5.0 | 0–10 | 18 | 0.5–5.0 |
| 325-1 concrete basins | 10.0 | 0–25 | 37 | 21 |
| 600-1 wooden basins (suspended culture) | 20.0 | 0–31.5 | 73 | 5 |
| 59-1 PVC basins (suspended culture) | 35 | 10–50 | 127 | 22 |
| Spray culture | 20 | 73 | 20 | |
Factors other than basin size and water exchange rate which could influence the growth rate are nutrient level of water, basin depth and amount of light (excess light might inhibit growth).
In Chile another kind of cultivation has been tried: the introduction of Gracilaria into new areas. This has been done north of its natural distribution. In the Isla Santa María in the Antofagasta area (II Region) stone-planting was attempted. Gracilaria was brought from Coquimbo and attached to stones of about 25 cm. In Bahia Inglesa and in Corresal (III Region) iron nets were used for the introduction of Gracilaria in bays where it has previously not been found. Initially stone-planting was cheaper than iron nets, but from 100 stones only 10 plants were received, while iron nets give a very high survival percentage.
Iron nets are very expensive. One Gracilaria fragment is attached at each crossing point, and within a short time the iron net sinks into the bottom and is buried by sand. Very good algal beds grow with this method. However, iron dissolves after a short time in the sea, and it is important to know if the algae remain after the net has disintegrated.
On the contrary, Lessonia grows on rocks in the most exposed fringe, where no other species have a chance to compete (in southern Chile it is replaced by Durvillea). Iridaea and Porphyra grow in fairly pure stands on their particular levels, and the best qualities of Iridaea, the deep-water species, are collected as drift material on beaches.
Transplantation is a close alternative to cultivation, and has been tried for Gracilaria to introduce the species in suitable bays where it is not growing naturally. However, the method is expensive, and the concept is that it should be necessary to introduce the alga only once; and then its growth should continue spontaneously.
Chilean shipments of Gracilaria have been rejected by Japanese buyers. This has even happened to the attractive quality from Isla Santa María because of the high degree of moisture produced by the quantities of fish eggs attached to the fronds.
It is possible that Chilean seaweed production could gain more by aiming at higher qualities rather than at larger quantities. Quality characters include the phycocolloid percentage of the (commercial) dry matter and also its properties: setting point, melting point, gel strength and viscosity. The prerequisites for upgrading procedures - suitable methods, costs and gains - require the attention of a project which should:
investigate in what respect some crops are inferior (taste or gel content or gel quality)
investigate the cause of such inferiority and how qualities and quantities change by season, depth, salinity and other factors
investigate possible counteractions.
In the USSR, Taiwan, Canada and France, Ahnfeltia, Gracilaria, Chondrus and Hypnea receive special treatment a few days after being harvested, and before being dried. Canadian studies have shown that the carraghenan content of Chondrus can thus be considerably increased. The principle is very simple: the algae to be upgraded are put into a large but not deep basin. They are given an environment rich in phosphorous and trace elements, but poor in nitrogen. As nitrogen is required for the synthesis of proteins, including enzymes, the plants cannot produce these and in a few days they lose colour and the carbohydrates increase at the cost of proteins. In Chondrus and Hypnea a pale quality is preferred, as bleaching of the final product is otherwise needed.
In Gracilaria the problem is different, as the Japanese prefer a dark product for human consumption. If it were known for which purpose a buyer wants the raw material, it would be possible to produce black Gracilaria for consumption and yellow for agar extraction.
An important problem to be overcome in Chile is the cost: good qualities of Gracilaria from Isla Santa María bring Pesos 10/kg while corresponding material from the nearby estuary of Tubul brings only Pesos 5/kg, and the large quantities from Rio Maullín still less.
What actually is the difference? The fishermen say the salty taste pleases the Japanese more, because they use it for human consumption: Is this really true? Or is the Chilean Gracilaria used for agar extraction, and do the marine plants have a higher agar content? The estuary material is contaminated with fine sediment particles from the river, but is notably free from epiphytes other than diatoms. Because of this, the buying company has a plant for drying and washing. The material, e.g., from Lota is first sun-dried on the beaches and then transported to the drying station, where it is washed (in fresh water) and dried on racks. The procedure is then repeated so that it is washed and dried twice in the same day. It should be determined if it loses in agar content (a) when being transported and stored in a half-dry condition; (b) in being washed and dried twice?
It is noted that the three localities reported as having the highest qualities are Piedra Azul, Isla Santa María and Caleta Lenga. These are open-sea prairies; while all the low-price qualities come from estuaries.
In Piedra Azul, and in Maullín the author observed a transport system of towing the fresh plant behind the boats in polyethylene net sacks. By this method, large quantities can be transported by a small boat and without the temperature increase which causes bacterial deterioration. It could be used to move low-grade river mouth material into full salinity seawater, where it could be dumped temporarily into a basin and left to assimilate and adopt the seawater plant qualities.
The basin system could be that used in some fish cultures: to be drained at the end of a low water period and to be refilled at high water.
The use of drift algae as manure has been known for a long time. In the Rio Maullín area Gracilaria was used as a fertilizer for potatoes before 1965, when extraction for agar was started. This is not the case today as all Gracilaria is sold.
In Isla Santa María a large part of what is brought ashore, in particular by beach collectors, consists of other species, primarily Macrocystis and Desmarestia, which are sorted from the rest and left on the beach. On this sandy island they would serve as excellent manure.
It seems generally known that seaweeds contain nutrients and micro-nutrients, but not that they have an extraordinary faculty as soil conditioners. After a rainfall their gels take in large quantities of water which they retain and only slowly give off during a dry period. All agriculture and gardening in dry regions could profit from seaweed manure (Senn and Kingman, 1978).
The utilization of algae for human food is widely known within Chile but is not promoted in any way by the authorities, and scarcely mentioned in the publications on seaweed utilization.
The red alga Porphyra is marketed under the name of “luche” and used for a stew similar to spinach. Pieces of about 400 g are sold at Pesos 20–30 (US$ 0.5–0.75). They are marketed fresh as they contain much water and could not withstand transport as they mould within a few days. In Japan, many species of the same genus are used for the preparation of “nori” sheets, with a retail price in western countries 100 times as high as that of “luche”.
Authorities could promote the benefits of these health-giving Chilean resources most easily by reinstating the practice of adding a seaweed meal to school lunches. Previous experiments in Chile were rewarding.
