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When it comes to food it is necessary to decide how self-sufficient the seastead should be. There is a spectrum of choices available from importing everything to producing everything locally. Realistically, seasteads are unlikely to be 100% self-sufficient due to lack of available space, capital, and the fact that people can only stand to eat so much spirulina algae. A reasonable goal for an early seastead is to grow its own fruits and vegetables and get some of its protein from aquaculture.
In ancient times, with transport crude, slow, and pricey, most trade involved goods with a high ratio of value to mass…But over the centuries, as transportation grew more cheap and routine, trade in bulky essentials grew practical. Even in the Roman Empire, hauling wheat long distances over water had made economic sense. [Wright2000]
Shipping food is clearly feasible, given how commonplace it is in the modern world. Staples like rice, wheat, and olive oil require a lot of growing area. Yet they are dense, inexpensive to purchase, and easily stored, which makes them ideal to import. So trade is always an option - and will be a necessity if a varied diet is desired on early seasteads. A small community simply cannot produce a large variety of items, so it will be a long time (if ever) before local seastead produce can rival the set of choices available in modern supermarkets. While residents will naturally cut back on imported foods, they’ll still want something different on occasion. (This has been true throughout human history). This will be less of an issue on tourism-based seasteads with a mainly transient population.
Another way to look at importing food is to consider the economic idea of comparative advantage, explained by David Ricardo in 1817. He demonstrated that nations prosper most by doing what they are relatively best at. Solar area on a seastead is expensive (we have to build our own land), and agriculture is an industry with a very low income per unit area. So, much like terrestrial cities, seasteads should focus on industries which are not space-intensive. While breakwaters may eventually render new land cheap enough for agriculture, early spar platform seasteads are not going to find it cost-effective. There is nothing unique about importing food, so we won’t go into detail.
There is a long history of people supplementing their diet with home grown vegetables. During World War II, these gardens were called `Victory Gardens’ and the name has stuck ever since. An excellent guide to home gardening is Square Foot Gardening by Mel Bartholomew [Bartholomew1981] (also made into a popular PBS series). This book is notable in that it tries to minimize the amount of time spent in the garden. Most other books seem to focus on gardening as a hobby and tend to soak up as much time as they can get. The goal of square foot gardening is to spend just a few minutes a day on garden maintenance. Its methods claim to produce enough fruits & vegetables for a person in only 4 m2.
One real advantage that the seastead has when it comes to growing crops is that it is possible to reduce or eliminate weeds and insect pests. This is extremely difficult to do on land, since the weeds and pests are just blown across the property boundary. With a seastead, which is naturally isolated from terrestrial ecologies, care can be taken to minimize the number of insects and weeds that take hold on the seastead.
While some items (fruit or nut trees) may be grown in dirt outside, we expect the majority of farming be done hydroponically in greenhouses. We present some data on how much area per person is required, but unfortunately our numbers are a bit rough. Also, they will depend strongly on the level of self-sufficiency and type of diet desired.
{ Talk about which plants? It matters a little, but enough? }
We expect seasteads to use greenhouses heavily, since they offer:
Hydroponics is a farming method in which plants are rooted in a liquid nutrient solution, rather than soil. This high-capital, high-yield industry has grown 4-5 fold in the past decade. Hydroponics has a number of advantages over conventional field farming:
The main concern of a seastead is yield per unit area, and many of the advantages of greenhouses and hydroponics are multiplicative on this quantity. For example, twice as many crops per year and twice as dense crop spacing would together mean a four-fold increase in yield. In practice, a factor of 5-10 times is common [Roselle1996], [Willis1992, Ch. 2]. Yields as much as 100 times higher have been achieved [Willis1992, Ch. 2].
It is reasonable to wonder whether these numbers are too good to be true. Keep in mind that we are just talking about crops per unit of area. Hydroponics does use other resources, like nutrients and water, more efficiently than conventional gardening, but this factor is much less than the yield/area factor we’re focusing on. For example, more crops per year means a better yield, but also more picking time, fertilizer used, etc. Another downside is that the capital costs of hydroponics can be quite high. Since farmland is relatively cheap, hydroponics are usually not worthwhile, even with the advantages listed above. On a seastead, however, solar area will be at a premium, and so a technique which minimizes area use is just what we need.
The figures we found for hydroponics equipment cost varied hugely, from $5/m2 for simplified home systems in the third world [Bradley2000] to $150/m2 for commercial first-world operations [AmericanHydroponics, sample costs]. There’s a good chance seasteads will be towards the expensive end of this range in order to maximize yield, but experimentation and DIY could bring costs back down. Empirical data gives yields for many hydroponically grown vegetables are of 50-250 g/m2/day.
It is important to be careful of water-borne diseases, since many plants share the same nutrient solution. For this reason, in most indoor operations, the growing medium is sterilized between crops [Willis1992, Ch. 2].
Gardening, even with hydroponics, will use considerable fresh water. Recently, scientists have produced genetically modified tomatoes which can be grown in saltwater. The plants extract salt from the water and store it in their leaves (which offers intriguing possibilities for reclaiming salinated land). The most exciting part is that the plants are made saltwater tolerant by the introduction of a single gene which codes for a protein for dealing with salt. This means mean that many plants could theoretically be modified in the same way. However, the plants are not able to deal with pure seawater. Also, we won’t be able to compost the salty leaves. So we save freshwater, but lose some organic material [Zandonella2001].
Note that GMO plants are unlikely to take over the ocean, since they can’t deal with pure saltwater and they need to be immersed in a nutrient-rich medium. In general, they are not adapted for the ocean, which makes them far less likely to spread than GMO’s on land.
No seastead diet would be complete without the one “plant” evolved for the ocean environment. Seaweeds are actually a form of algae, and people have been eating them for thousands of years, particularly in the Orient. None are known to be poisonous, although some can cause discomfort. Extracts such as agar and carrageenan are derived from sea plants and used in a large variety of packaged foods. Seaweeds are rich in vitamins, minerals, and protein, and can be used to fertilize other plants. Ironically, the vitamin C in seaweed might have saved early seafarers from scurvy, if only they’d known to scoop it up! [Neumeyer1982, Chapter 6].
Seaweed can be cultivated by placing fragments on ropes or other substrata and growing them in the ocean.
Spirulina has the most remarkable concentration of functional nutrients ever known in any food, plant, grain, or herb. On top of this, spirulina delivers more nutrition per acre than any other fod on the planet. This has extraordinary implications for more efficient and less damaging food production for the future. Every day new research brings to light the wonders (hidden) in microscopic algae.
[Spirulina1994, p. 5-6]
While books like Earth Food Spirulina can sound a bit over-the-top at times, author Robert Henrikson knows the subject well - he’s the president of Earthrise Farms, the largest spirulina farm in the world . Blue-green Spirulina algae, used as food by the Aztecs , is 65% protein by weight, and is a complete protein source. Because it is such a simple life-form, it is much easier to grow and harvest than crops or livestock. Algae waste no growth on inedible parts, and every cell is a seed. Their life-cycle is simple, and they grow at an exponential rate until nutrients are exhausted (doubling biomass every 2-5 days). Spirulina can grow in sea water, and be eaten without any processing. It contains vitamins as well, including A, E, and B12 [Spirulina1994].
It has been suggested that spirulina provides more nutrition per acre than any other food - and without requiring fertile soil or fresh water. Current production costs in large facilities range from $10-$20 / kilo. Compared to the extravagant conventional methods of obtaining protein from mammals, spirulina provides an incredibly efficient one-step food chain, as can be seen in the table below.
Resource Usage To Produce One Kilogram of Protein:
(Parenthetical italics indicate values relative to Spirulina)
Land (m2) Water (Liters) Energy (Gigajoules)
Spirulina 0.5-1.0 (non-fertile) 2,500 (brackish) 5.5
Soybeans 16 (16-32) 8,860 (3.5) 11.7 (2.1)
Corn 22 (22-44) 12,300 (4.9) 5.5 (1)
Grain-fed Beef 193 (193-386) 104,000 (42) 456 (83)
Another advantage of spirulina is that it produces oxygen as a positive externality. Unlike some algae, it is not nitrogen-fixing, and so requires a supply of nitrogen (perhaps from an artificial upwelling, such as a wave pump. One intriguing use for spirulina is to concentrate nutrients from seawater so that they can be used to feed more complex life forms. While spirulina thrives in salty and alkaline water, most strains don’t grow well in seawater, which has low carbonate and high magnesium and calcium. But special seawater strains are being developed.
Fungi are another lower life-form which can be used as a food supply. Protein derived from them is called mycoprotein, and produced by continuous fermentation. It has the advantage of being “chewy”, as well as absorbing added flavors and colors. Unfortunately, as reported by the CSPI, there have been many negative health reports about the commercially available mycoprotein [CSPIQuorn]. Medical investigation suggests that individuals with mold allergies may be allergic to mycoprotein as well [Hoff2003]. This problem seems to occur only in a minority of the population, but we advise caution, since serious allergic reactions can be fatal. Still, this is another potential way to grow protein.
Resources necessary for food production include water, light, fertilizer, labor, and space. Light is provided by the sun, water by the methods outlined earlier, labor by the residents, and space by the seastead. Fertilizer is a more complicated issue, as this excerpt from an article on space station biosystems demonstrates:
Previous work on hydroponic systems have shown that nitrogen balance cannot be achieved, especially with systems that involve organic matter (Jewell et al. 1993). Some nitrogen “leaks” from hydroponic systems, most likely as a result of micro anoxic environments where conditions for microbial denitrification are favorable. These conditions include zero dissolved oxygen and the presence of biodegradable organic matter. When these conditions occur many bacteria have the capability to use electrons from oxidized forms of nitrogen [ NO3- (nitrates) and NO2- (nitrites)] and reduce these valuable plant fertilizers into unavailable nitrogen gas. In sewage treatment hydroponics, between 25 and 50% of nitrogen has been observed to be unaccountably, presumably because of denitrification.
Hydroponic systems that maintain water free of biodegradable organics, high oxygen levels, and low oxidized nitrogen concentrations will discourage loss of nitrogen via denitrification. A conservative design would assume that as much as a quarter of the cycling nitrogen will be converted to nitrogen gas (N2 ), or a total mass of 15 g of nitrogen must be transformed from N2 to organic nitrogen each day in a closed biosystem.
A sustainable system must replace this nitrogen fertilizer loss via nitrogen fixation. Two biological options are available to convert N2 to organic nitrogen which can be subsequently biologically regenerated as ammonia-nitrogen or nitrate-nitrogen: symbiotic N2 fixation in legumes and N2 fixation in blue-green algae. An option that could be used to generate useful biomass with minimal side affects would include symbiotic N2 fixation using legumes, possibly food producing legumes such as soybeans.
Unfortunately, nitrogen fixation is a highly energy intensive process, and rates are relatively slow. Depending on the length of growing season, documented fixation rates vary from 0.008 to 0.18 g N/m2 -d. Growing areas to make up a 25% loss would be 83 m 2 to 1,900 m2 . This nitrogen management plant area could be equal in size to hydroponic food production. It will be assumed that no human food results from the nitrogen fixing hydroponics.
A summary overview of the closed biosystem for one adult is shown in Figure 5. Total plant growth area is 290 m2.
[Jessell2001, pp 9-10]
Fortunately, we don’t need to manage our nitrogen balance quite as carefully as a space station. For instance, we can purchase nitrates produced on land using the Haber-Bosch process. Those seasteads which seek completely sustainable farming, however, must keep this problem in mind. Composting and similar closed-cycle techniques can reduce the amount of new fertilizer needed. Composting is covered in both Building for Self-Sufficiency and Square Foot Gardening. There may eventually be clever methods of extracting fertilizer from the ocean (artificial upwelling, concentrating nutrients with algae, etc.). But until then, even with these techniques, some fertilizer will need to be imported.
Artificially lighting a greenhouse to produce a longer growing day takes about 50 - 175 W / m2 of power [MBR, Ch. 5], [Andrew1994]. At 20m2/person, this would be 1 - 3.5 kW / hr. So 12 hrs/day, 365 days/year of lighting would use 4-15 mWhrs/person/year, which is significantly more energy than is required for personal use. Since power onboard a seastead is expected to be expensive, this will probably not be worthwhile. For example, using photovoltaic panels for this purpose would be absurd, since they’d take up around 10x as much space as the plants they were providing electricity to light! Still, it is possible that special factors (excess power, cheaper power generation, trade embargo) could change this.
There are some other ways we might increase grow area. Mirrors or other sunlight collection devices could be used to gather sun from a larger area than the platform, lighting a second deck. Another possible solution would be to make small rafts or barges as auxiliary grow areas. They would be constructed cheaply, only able to withstand typical non-storm seas, and deployed around the stead. They would be sized so that in foul weather they could be hoisted up under the stead for protection. Fresh water could be piped to the units, or they could contain integrated [solar stills][].
There are several ways we may be able to supplement the production of our gardens, such as fishing, aquaculture, and raising farm animals.
Fishing is heavily regulated inside EEZs, so it may be problematic. Also, a seastead can’t just zoom around looking for fish like boats do. However, seasteads may find fishing economical if they are in locations where the stock has not been depleted by commercial farmers. This could even make for a profitable seastead business.
Aquaculture, the process of raising ocean foodstuffs, is the maritime equivalent of ranching. This practice has a long history: Chinese manuscripts indicate that fish culture has been practiced there since at least the 5th century BC, and the Romans raised oysters. The list of animals that have been raised commercially starts with Abalone, Amberjack, Anchovy, and continues on for another 100 species [WorldAquaculture].
Unlike the commercial fishing industry, which is slowly succumbing to the exhaustion of its commons, aquaculture systems offer long-term promise. This is true whether you look at it from the environmentalist’s perspective of increased sustainability, or the economist’s viewpoint of more clearly defined property rights. Given the incredible impact of the agricultural revolution, we can’t help but speculate that the movement from hunting wild fish to farming domesticated ones will also produce major gains in efficiency and worldwide food production.
Saltwater plants dovetail nicely with aquaculture because the waste products of fish can be used to fertilize plants. This system is called Aquaponics. For example, on Carl Hodges’ experimental farm, shrimp grow in saltwater, then tilapia, and then the water is used to nourish a saltwater plant called Saliconia (used for vegetable oil) [Hinman1996].
Aquaculture is roughly divided into intensive and extensive. Intensive is more complex, as it involves creating an artificial environment in which to raise the product. Extensive can be as simple as “fencing” off a section of ocean with nets, and raising some fish inside it. By choosing species which feed on the natural detritus of the ocean such as algae, no food supply is needed. While this tends to be a low-density, slow-growth method, it’s also low-effort and uses renewable resources. N55’s SMALL FISHFARM is an example of a simple design [N55BOOK, pp. 167-176].
Raising a small number of dairy animals will probably be worthwhile, such as chickens (for eggs) and cows (for milk). Chickens run about 8 to the square meter [SpaceSettlements, Ch. 5], although growing their feed will use area as well. Chickens, cattle, rabbits, and similar animals can be grown for meat, producing edible portions of about 1/5th to 1/10th of the mass they consume [SpaceSettlements, App. C]. Unless a cheap food source like algae can be fed to animals, importation is probably a better way to get meat.
{ more numbers would be great here, if anyone has them }
Numbers in the literature on the area required for self-sufficient food production vary widely. This is not surprising, since the environments discussed are very different. Meat takes much more space than vegetables and starches, and a complete diet takes much more space than supplementary fruit, vegetables, and dairy. Conventional, open-field agriculture uses a lot more room than hydroponics on a space station.
We think the latter is more relevant to us than the former. Common sense tells us that when a resource is scarce, people find ways to use less of it. Farmland is much cheaper than seastead deck space, so we will use the latter more efficiently. We’ll have to use more of other resources to do this of course - if there was a way to use less space with no cost, it would already by part of standard practice. But while we aren’t getting something for nothing, we can be pretty sure that our yield per unit area will be higher than on land. One advantage we have compared to space stations is that we can draw from the resources of the ocean, including fish, seaweed, and nutrients, as well as importing from the outside world.
A representative land-based figure is the Biosphere II project, which attempted to be a completely closed ecosystem. They grew 80% of their food on 253 m2/person, which would mean 316 m2/person for self-sufficiency.
Food requirements are about 3.1kg [Shipman1989], and 2000-3000 cal per person per day. A NASA project on space station design says that about 15-50 m2 of solar area are necessary to provide a standard North American diet with high-yield techniques [SpaceSettlements, Ch. 3 and App. C]. This includes cattle and chicken raised for meat, which are area-intensive. On the other hand some of their numbers strike us as a bit optimistic. A different space station study suggests that all area required for complete self-sufficiency, including waste / water recycling, food self-sufficiency, and nitrogen balance, is 290 m2/p [Jewell2001].
Sailing the Farm, a book about self-sufficient boating, implied that using a cabin for food production (5-10 m2) could make a substantial contribution to the sailor’s diet. As mentioned earlier, Square Foot Gardening states that only 4 m2 / p are necessary for fresh vegetables.
Based on these figures, complete self-sufficiency would require about 50-300 m2 / p, which is not practical at current cost estimates. However, a substantial amount of food (vegetables, fruit, dairy) can be grown in only 5-20 m2 / p. Fishing, aquaculture and dense imported foods (grain, cheese, meat) will round out the seastead diet. Vegetarian tendencies and a willingness to eat unusual things like algae will shift seasteads farther towards self-sufficiency.