Life
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The general concepts embodied by 3D Ocean Farming have long been practised in China, where over 500 square kilometres of seaweed farms exist in the Yellow Sea. The seaweed farms buffer the ocean’s growing acidity and provide ideal conditions for the cultivation of a variety of shellfish. Despite the huge expansion in aquaculture, and the experiences gained in the USA and China of integrating kelp into sustainable marine farms, this farming methodology is still at an early stage of development. Yet it seems inevitable that a new generation of ocean farming will build on the experiences gained in these enterprises to develop a method of aquaculture with the potential not only to feed humanity, but to play a large role in solving one of our most dire issues—climate change.
Globally, around 12 million tonnes of seaweed is grown and harvested annually, about three-quarters of which comes from China. The current market value of the global crop is US$5–5.6 billion, of which $5 billion comes from sale for human consumption. Production, however, is expanding very rapidly.9 Seaweeds can grow very fast—at rates more than thirty times that of land-based plants. Because they de-acidify seawater, making it easier for anything with a shell to grow, they are also the key to shellfish production. And by drawing CO2 out of the ocean waters (thereby allowing the oceans to absorb more CO2 from the atmosphere) they help fight climate change. The stupendous potential of seaweed farming as a tool to combat climate change was outlined in 2012 by the University of the South Pacific’s Dr Antoine De Ramon N’Yeurt and his team.10 Their analysis reveals that if nine per cent of the ocean were to be covered in seaweed farms, the farmed seaweed could produce twelve gigatonnes per year of biodigested methane that could be burned as a substitute for natural gas. The seaweed growth involved would capture nineteen gigatonnes of CO2. A further thirty-four gigatonnes per year of CO2 could be taken from the atmosphere if the methane is burned to generate electricity and the CO2 generated captured and stored. This, they say:
could produce sufficient biomethane to replace all of today’s needs in fossil-fuel energy, while removing fifty-three billion tonnes of CO2 per year from the atmosphere…This amount of biomass could also increase sustainable fish production to potentially provide 200 kilograms per year, per person, for ten billion people. Additional benefits are reduction in ocean acidification and increased ocean primary productivity and biodiversity.11
Nine per cent of the world’s oceans is not a small area. It is equivalent to about four and a half times the area of Australia. But even at smaller scales, kelp farming has the potential to substantially lower atmospheric CO2, and this realisation has had an energising impact on the research and commercial development of sustainable aquaculture. But, like CST technologies, kelp farming is not solely about reducing CO2. In fact, it is being driven, from a commercial perspective, by sustainable production of high-quality protein.
One fundamental point about kelp farming is that N’Yeurt’s vision cannot be fulfilled simply by scaling up current farming models. Existing farms are all located either onshore (Arcadia Seaplants Ltd in Nova Scotia, Canada, being the largest onshore facility) or in near-shore waters. This is because proximity to market reduces transport and other logistical costs, and the infrastructure requirements for near-shore seaweed farming are well understood. But near-shore environments are limited in extent, already face high usage for other purposes, and are vulnerable to ecosystem damage. Moreover, the issue of storing the carbon captured by seaweed in near-shore environments is a formidable challenge. If kelp farming is to reach its full potential, a model for mid-ocean farms is required.
The first person to think seriously about open-ocean farming of kelp appears to have been the American physicist Howard Wilcox. In 1968 he was working as a consultant to President Lyndon Johnson’s Commission on Ocean Resources. He felt that open-ocean kelp farms might provide food, animal feeds, fertiliser and energy at a large scale.12 While immensely challenging from a technical perspective, enough work has already been done to demonstrate that PV-powered mid-ocean kelp farming (PMKF) is feasible, and that while its development is expensive, it has considerable advantages over near-shore farms, particularly when it comes to storage of the captured CO2.
There are thousands of species of seaweeds, but the organism most often considered for the large-scale capture of carbon offshore is the giant kelp Macrocystis pyrifera. Contrary to popular belief, giant kelp is not a plant, but rather is classified along with other algae in the phylum Heterokontophyta. Giant kelp is the largest of all algae, and one of the fastest-growing of all organisms. In ideal conditions it can grow sixty centimetres per day, and its fronds can reach lengths of up to sixty metres. Giant kelp occurs naturally on the Pacific coasts of the Americas, and in the waters of Australia, South Africa and New Zealand, where it forms dense ‘forests’. Anyone who has walked an ocean beach adjacent to an offshore kelp forest will recognise its great leathery blades and floats that are washed ashore, often in great rafts. Giant kelp is, moreover, a keystone species—it supports thousands of other species as diverse as invertebrates, fish and even mammals such as the sea otter. As long ago as the mid-nineteenth century, Charles Darwin speculated that its marine forests rivalled the tropical rainforests in diversity—a view supported by decades of subsequent research. As the marine biologists David Schiel and Michael Foster say, ‘Perhaps no other single species is so important in providing biogenic habitat in which thousands of species can live and interact.’13
Giant kelp has been harvested from the wild for over a century. It has even been grown commercially as a valuable source of soda ash (an ingredient used in glass and detergents), alginates (gel-like substances used for many things including thickening foods), iodine, potassium, vitamins and minerals. More recently, it has become of interest as a feedstock for farmed abalones and shrimps. Other seaweed species, however, are preferred as a food for humans.
The 1972 oil crisis saw researchers turn to giant kelp as a possible source of biofuel, though this interest lapsed as oil prices fell. More recently, the climate crisis has seen a growing interest in farming giant kelp to sequester atmospheric CO2.
Despite its many favourable characteristics, growing giant kelp in any sort of farm—much less mid-ocean farms (PMKF)—is not straightforward. The species has a complex life cycle, with generations alternating between a microscopic sexual phase (in which the miniscule kelp organisms exist as separate sexes), and the much larger organism we recognise as mature giant kelp. China has taken the lead in giant kelp cultivation. In the Chinese method, the tiny sexual phase of the organism is cultivated in cooled greenhouses where conditions are tightly controlled, and which are located onshore, then the larger phase is transplanted onto long lines laid out in the sea, either on the surface or at shallow depth.14 In the past, both China and the USA have made efforts to grow giant kelp far out to sea, suspended from floating frames. The Chinese discovered that the kelp, freed from the constraints of near-shore waters, grew to a large size. But operational challenges, principally surrounding the culture of the sexual phase of the organism in an offshore environment, along with problems concerning the maintenance of the floating structures, saw the Chinese projects shelved.15
In 1973, inspired by Wilcox’s pioneering work and spurred by the oil crisis, the Californian Institute of Technology and the US Navy joined forces to conduct large-scale research into oceanic kelp farming. The research was to extend over ten years and to cost several billion dollars. A series of farms was established, the first being a three-hectare array off San Clemente Island, California, which was an anchored structure floating in waters 125 metres deep. It and subsequent attempts fell victim to the sometimes extreme weather conditions seen along coastal California, and the farms were wrecked by storms. Despite the setbacks, the American Gas Association joined the program, ultimately contributing US$2 billion to it. A series of experimental structures yielded valuable experience about almost all aspects of kelp farming, before they too were closed as a result of design flaws and accidents.
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br /> The most long-lived of the farms built under the project was a shallow-water farm established in 1981 near Goleta, California. Experiments conducted there established that growth rates of giant kelp subject to the technologies expected to be used on deep-ocean farms were at least equivalent to those of naturally growing kelp. Other experiments proved that the kelp could be fed by pumping nutrient rich water from a depth of 350 metres to the surface, and that the kelp were able to reproduce on the farms—reproduction was a major stumbling block in the Chinese efforts.16 These pioneering experiments came to an end when interest in using kelp for biofuels faltered, again as a result of dropping oil prices. Perhaps it’s not surprising that farms anchored to the bottom in such a turbulent environment as coastal California would fall victim to storms. But back then, free-floating mobile structures were barely feasible.
Interest in utilising the open ocean for crop production has been revived, and the results of early work are being examined. Much has changed since the 1980s, when the last efforts to grow giant kelp at large scale in the open ocean were made. Among the most important are huge advances in computing, GPS technology, weather prediction, the availability of solar power and new materials such as carbon fibre. Together, these advances mean that today open-ocean kelp farming has a better chance of succeeding than ever before.
Given the prominent role that bad weather played in the failure of earlier kelp farming, it’s clear that location is an important factor. There are regions of the ocean where calm conditions prevail, such as the rainy intertropical convergence zones that circle the Earth about thirty degrees north and south of the equator. Known in the age of sail as the ‘doldrums’, they are characterised by very still weather. Their precise locations and extents vary according to global atmospheric circulation patterns, and occasionally thunderstorms can disrupt the calm. But their generally tranquil conditions make them ideal for kelp farms. Given the likelihood that future, doldrums-based kelp farms would be mobile, and perhaps capable of submerging for a time to avoid storms, and given advances in weather prediction, it seems that weather damage to such farms could be minimised.
Much of the surface of the deep ocean is a biological desert. There is no life there because there are no nutrients. When it comes to kelp farming this is potentially beneficial, because it means that any farms operating there will not impact fragile ecosystems, or be impacted by them. But where would the nutrients to feed the kelp come from? It turns out that they are just a few hundred metres away. In 2010, researchers with Monterey Bay Aquarium Research Institute confirmed earlier studies showing that nitrates and other nutrients essential for algae to grow abound as close as 250 metres below the surface. The occasional algal bloom that is observed in what is otherwise a desert sea all but devoid of life occurs when deep currents bring those nutrients near enough to the surface for sunlight to reach them.17
The amount of energy required to pump water from a depth of about 300 metres to the surface is relatively trivial and could be easily supplied by solar-powered pumps. Indeed, solar technology is more than capable of providing the power for this as well as the other requirements of a mid-oceanic kelp farm, such as transport, refrigeration and lighting.
Giant kelp is not the only species suitable for stocking such farms. Bull kelp (Durvillea), which occurs at high latitude in the Southern Hemisphere, and vast expanses of floating sargassum weed (Sargassum), which grows in the Sargasso Sea region of the Atlantic Ocean as well as elsewhere around the globe, offer further possibilities. Nor are the doldrums the only option in terms of location. The North Pacific garbage patch is a huge gyre that extends from 135° to 155° West, and 35° to 42° North. Most of the garbage consists of plastic particles suspended below the surface, and it seems possible that seaweed farming in this region could be linked with clean-up efforts, perhaps even using the plastic as fuel. And a clean-up is much needed because plastics from the gyre kill about a third of all albatross chicks born on Midway Atoll each year, as well as having a large impact on marine turtles and other marine life. Another unfortunate effect occurs as the plastics break down and release toxins including hormone disruptors that are consumed by microscopic creatures and jellyfish, then concentrated in fish, potentially arriving on our tables after bio-concentration.
How might such a clean-up operate? The plastic in the great North Pacific garbage patch is not, as you might imagine it, tightly packed, but diffuse, with about four, mostly small, pieces of plastic floating in every cubic metre of water. Interspersed with chemical sludge, it adds up to just 5.1 kilograms of waste per square kilometre of ocean surface.18 Some work is already being done to deal with the problem. The Ocean Clean-up, founded by Dutchman Boyan Slat, focuses on inventing and developing technologies to deal with oceanic pollution.19 It has already received over US $2.2 million through crowdfunding and sponsorship. Its vision is to use ‘passive cleaning’ to collect the plastics from ocean gyres. One-hundred-kilometre-long floating V-shaped barriers would be anchored to the sea floor, and the gyre currents themselves would concentrate the plastics in them. The project has won various awards, but remains in its earliest stages of development. There are plans to launch a pilot program using two-kilometre-long barriers off Japan. If the plastic waste can be captured, it could be burned or charred for energy, or compacted and encouraged to sink to the floor of the abyss, or perhaps be recycled. The entire process could be powered from bioenergy created from seaweed farming. Because, in most scenarios, there is no commercial product from such a process, it would have to be funded as a public good.
Not all kinds of blue-water kelp farms would have to float. The ocean has vast submarine plateaus to which farms could be anchored. The Saya de Malha Bank, north east of Madagascar, is the largest submerged plateau in the world, with about 40,000 square kilometres of area lying at depths of between seven and seventy metres. When combined with Lansdowne Bank, a seamount located between Australia and New Caledonia, which has an area of about 21,000 square kilometres at depths of between sixty and eighty metres, over 60,000 square kilometres of shallow, mid-ocean area is useable. In such places, farms could be anchored and may be cheaper to build and maintain than those that float. Unlike farms located over deeper water, however, carbon-rich material (such as kelp by-product, or CO2 itself) could not be sequestrated in the ocean depths, so alternatives would need to be found. One of the recurring problems for all such options, however, is likely to be cost. How could blue-water kelp and shellfish compete commercially with aquaculture located closer to cities? A carbon price might give them a competitive advantage, as perhaps could ecological or overall increased productivity benefits.
The importance of a carbon price if seaweed is to be used to sequester carbon has been emphasised in a recent research paper.20 About 27.3 million tonnes of seaweed was grown globally in 2014. Only South Korea, responsible for six per cent of global production, has a blue-carbon program (effectively a carbon price) that includes seaweed. Demand for seaweed continues to outstrip supply. Norway, for example, is encouraging seaweed farming, and the area under cultivation tripled between 2014 and 2016. Seaweed use in biofuel and fertiliser production and as a feedstock for cattle to reduce methane emissions are all growing markets, which means that, in the absence of a carbon price, the amount of seaweed remaining to be disposed of in shallow marine sediments (around seaweed farms) is decreasing.
As more farms are developed, the gap between supply and demand is diminishing, and the price seaweed growers receive is declining by one–two per cent per year. This discourages new growers, but opportunities continue to emerge, including seaweed farms co-located with offshore wind farms, and farms positioned to reduce wave size, and thus slowing coastal erosion.21
What might a PMKF facility of the future look like? Dr Brian von Hertzen of the Climate Foundation has outlined one vision: a frame structure, most likely composed of a carbon polymer, up to a square kilometre in extent and sunk far enough below the surface (about twenty-five metres) to avo
id being a shipping hazard. Planted with kelp, the frame would be interspersed with containers for shellfish and other kinds of fish as well. There would be no netting, but a kind of free-range aquaculture based on providing habitat to keep fish on location. Robotic removal of encrusting organisms would probably also be part of the facility. The marine permaculture would be designed to clip the bottom of the waves during heavy seas. Below it, a pipe reaching down to 200–500 metres would bring cool, nutrient-rich water to the frame, where it would be reticulated over the growing kelp. Dr Von Herzen’s objective is to create what he calls ‘permaculture arrays’—marine permaculture at a scale that will have an impact on the climate by growing kelp and bringing cooler ocean water to the surface. His vision also entails providing habitat for fish, generating food, feedstocks for animals, fertiliser and biofuels. He also hopes to help exploited fish populations rebound and to create jobs. ‘Given the transformative effect that marine permaculture can have on the ocean, there is much reason for hope that permaculture arrays can play a major part in globally balancing carbon,’ he says.