Kelp farming in New Zealand has an obvious future as a macro-algae concentrate for soil and plant health, as an ingredient in various specialty food products and additives, as cattle feed and for the top dressing of pasture. Whether it can ever be farmed in sufficient quantity to act as a useful adjunct to carbon sequestration efforts on land remains to be seen. In her interview with Kim Hill on National Radio recently (12 October), Dr Marjan Van Den Belt mentioned a back of the envelop calculation that apparently showed that if a way could be found to grow kelp on offshore floating platforms in New Zealand’s EEZ, the amount of kelp required to offset ALL of New Zealand’s greenhouse gas emissions would take up a mere 2% of our EEZ.

NZ will need to focus on both land-based and ocean resources to meet its carbon zero goals

Which future do you prefer?
A tree in a field

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Current policy in New Zealand towards the lowering of our greenhouse gas emissions is focussed on the land-based economy. But now there is a new reality. If we are to meet our zero carbon goals, New Zealand will need to think of both its land and its oceans as comprising a single interlinked system. To date, it is land use issues which have dominated much of the discussion around zero carbon. At the New Zealand Oceans Foundation (, we think that government needs to give urgent attention to how New Zealand’s oceans might also contribute, along with the land-based economy, to meeting our Paris commitments and the government’s zero carbon goals.

Transition pathways

The most authoritative discussion on transition pathways to a lower emissions economy is contained in a report by the Productivity Commission. This report was released in August 2018:

‘Being asked to advise on how New Zealand can best make the transition to a low emissions economy, while at the same time continuing to grow incomes and wellbeing, is perhaps the most profound and far-reaching mandate the Commission could be tasked with. After an extensive inquiry process, we conclude that New Zealand can indeed make this transition. But there will be tough challenges along the way. It will require consistent and concerted effort across government, business, households and communities – up to and beyond 2050. Among the numerous changes that will be required across the economy – some disruptive some less obvious – three particular shifts must happen for New Zealand to achieve its low-emissions goals: 1) we stop burning fossil fuels and where possible, switch to use of electricity and other low-emission energy sources; 2) we undertake substantial new afforestation (our emphasis); and 3) we make changes to the structure and methods of agricultural production.’[1]

The role of New Zealand’s oceans

There is nothing in the report of the Commission on how New Zealand’s oceans might contribute to a lower carbon emissions economy through carbon sequestration, or carbon capture and storage. The solutions offered are all land-based.

This is puzzling on at least two counts. First, our oceans are 15 times more extensive in area than our land. Second, the oceans are the world’s greatest carbon sink. If ways could be found to increase the carbon sequestration potential of our oceans, without acidifying or warming them further, or to use the Maui offshore gas fields for carbon capture and storage, this seems to us to be an approach worth committing to. Not instead of necessary changes in land use, or of efforts to reduce greenhouse gases in the first place, but as a supplement to land-based efforts and in order to reduce the potential negative impacts of policies based solely around the land-based economy.[i]

Framing the zero carbon response only in land-based terms ignores an important reality. New Zealand’s land and oceans are a single strategic entity. What happens in one affects the other. Developing our oceans-based economy requires the contribution of resources that only our land-based institutions can provide. Lifting our national wealth, remediating land-based environmental damage and lowering our carbon emissions will require the resources that only the oceans can provide.

Large scale afforestation

We will come back to the role of the oceans. First, some background on afforestation, aspects of which appear problematic.

On large scale afforestation, the Productivity Commission comments as follows:

‘Forestry offsets just under one-third of New Zealand’s gross emissions. Yet, because planting rates have dropped sharply since the planting boom in the 1990s, and many of these forests are shortly due for harvest, carbon offsets from forestry are likely to decline if there is not a significant increase in planting. Land use will need to change substantially if New Zealand is to transition to a low-emissions economy by 2050. In particular, land planted in forests will need to increase by between 1.3 million and 2.8 million hectares, mostly converted from marginally profitable beef and sheep land.’ (pg 325ff Productivity Commission report at

Under this approach what percentage of New Zealand’s land needs to be taken for new afforestation? Our land area is 26.8 million hectares of which roughly one third is in the conservation estate. Mature forests cover 29% of New Zealand’s land area and a further 8% is planted out in commercial forests (mainly in pinus radiata). This means that 37% of New Zealand’s land area is already in forest. If a further 2.8 million hectares is given over to a new mass afforestation programme this will add another 10%, at which point the proportion of New Zealand’s land area covered in forest will be a total of 47%. Very nearly half of all our land will be in either mature or plantation forest.

Practicality and desirability

How likely is it that this much land can be found for new forestry? The Productivity Commission advises as follows:

‘New Zealand has sufficient suitable land to greatly expand afforestation to sequester carbon. This land includes over a million hectares of highly erodible land unsuited to pastoral agriculture (though some of this is also unsuited to forestry). The land is both privately and publicly held. The availability of privately held land will depend on the economics, including the prospective price of NZUs[ii] over the growing period and at harvest. The availability of government-controlled land for further afforestation is uncertain.’[iii]

A herd of sheep standing on a lush green field

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That a significant new programme of afforestation will be required if New Zealand is to meet its zero carbon goal seems beyond doubt. Yet a massive afforestation programme has its problems, not the least of which is the willingness of New Zealand’s sheep and beef farmers to see their more marginal land converted to forestry. There does not seem to be any stocktake readily available of just how much marginal land is suitable for afforestation even if the economics are compelling. The Productivity Commission refers to ‘over a million’ hectares of land as unsuited to pastoral farming, but this is well short of the 2.8 million hectares the Commission envisages being needed for afforestation if New Zealand is to meet its carbon zero goals.

Pinus radiata

There are other problems. If pinus radiata turns out to be the main production species planted, this is not a permanent solution to carbon sequestration since harvesting releases a portion of the carbon back into the atmosphere, and the carbon otherwise ends up being exported as logs or sawn timber, which simply transfers New Zealand’s carbon problem to other jurisdictions. Moreover, if a radiata pine forest is left untended and unfelled, after the carbon planting credits have been pocketed by investors after a quick dollar, it will eventually die (the life of pinus radiata is less than a 100 years) and be replaced by low value scrub and secondary growth of dubious economic value.

There are other objections to pinus radiata related to the effects on landscape and cultural values, and concerns over biodiversity. The Environmental Defence Society does not support a massive expansion of monoculture pine plantations across New Zealand’s landscape, partly because of the decrease in biodiversity and the risks of monoculture planting and partly because of the negative effects on landscape quality and tourism. Overseas visitors do not come to New Zealand because they want to see mass plantings of pine forest.

New approaches to carbon zero required

As the Productivity Commission has noted:

‘It is important to recognise the temporary nature of forest sequestration. Because there are limits to how much forestry the country can sustain, forestry will only buy time. In the longer term, new approaches to bring net emissions to zero will be required. It is critical that emissions reductions in other parts of the economy continue alongside afforestation.’

MOTU Economic and Public Policy Research ( have picked up on this theme in a recent research note on ‘New Offset Options for New Zealand’.

The note synthesises the current state of scientific knowledge around the issues associated with three innovative carbon reduction or removal options in a New Zealand context: soil carbon; marine carbon (sometimes called blue carbon) and carbon capture and storage.

Kelp save the world

At a recent Climate X Sprint event sponsored by the Climate Leaders Coalition, a team calling itself ‘Kelp save the world’ won with a presentation based on the use of seaweed as a Climate X (blue carbon) solution. Aiming to become the ‘Fonterra of seaweed’ its story was based on the following pitch:

‘Seaweed grows 30% faster than land based plants, sequesters 2.3 times more CO2 than pine, requires no additional fertiliser, feed or watering, doesn’t compete for land with other industries, reduces ocean acidification and naturally sheds 11.5% of its biomass while growing – permanently sequestering any stored carbon and removing it from the cycle.

‘Seaweed also has some incredible end-user applications – it is able to be used in agar (petrie dishes), it can be used as a biogas, can be eaten (hello sushi!), is a natural fertiliser – cutting down on nitrates in agriculture and can be turned into PHA plastics that can replace polyethylene, polyurethane and polypropylene. Research is also just coming to light that suggests as little as a 2% supplement of seaweed in cattle feed could reduce cattle methane emissions by as much as 50%! Also, as the emissions trading scheme matures and legislation catches up, seaweed carbon credits could be traded on the ETS.’

The link is at:

Carbon sequestration and capture: a role for New Zealand’s oceans

When thinking about a possible contribution from our oceans to meeting New Zealand’s Paris commitments, three broad approaches are possible: (i) farming kelp; (ii) carbon capture and storage in the Maui offshore natural gas fields; and (iii) understanding and potentially manipulating photosynthetic processes at the quantum level.

In this commentary we discuss the large-scale farming of kelp. In further commentaries we will look at carbon capture and storage and photosynthetic processes in our oceans.

Blue carbon: kelp farming as a complement to afforestation

An introduction to the role of marine ecosystems in sequestering carbon is contained in a recent paper by Harvard graduate students Sylvia Hurliman and Hannah Zucker. Coastal ecosystems such as mangroves, sea grass and kelp sequester surprisingly large amounts of carbon – up to 20 times more per unit area than land- based forests. Moreover, in the case of kelp, which is a macroalgae, the claim is that much of the carbon ends up being stored permanently on the deep ocean seabed in the form of plant detritus.

A close up of a map

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Pathways for sequestration of macroalgae carbon into the deep sea 

The link to Hurliman and Zucker (July 2019) is at: We note that Hurliman and Zucker quoted a much higher sequestration multiple for kelp over pine forests (up to 20 times) than the ‘kelp save the world’ team. This team quoted a multiple of 2.3 times. Whatever the multiple there is agreement that kelp outperforms pine forests on a unit area basis.

New Zealand giant kelp: Macrocystis pyrifera

New Zealand’s largest and fastest growing species of kelp is Giant Kelp or Macrocystis pyrifera. Sometimes known as bladder kelp, it is often seen washed up on beaches and shorelines around New Zealand. It has been described as the world’s fastest growing plant as well as one of the most ancient plant species in the world. It forms large forests in the deep sheltered waters around the South Island of New Zealand and can be recognised by the gas filled pods at the base of each frond. These bouyant pods help hold the fronds upright in the water, exposing them to the maximum amount of sunlight, aiding their efficiency at photosynthesis and contributing to their extremely rapid growth rate.

Kelp may be much more efficient per unit area at carbon sequestration than land-based pine forests. The question is whether or not it can be farmed in the marine environment of New Zealand (as distinct from growing wild) and, if so, whether the additional hectares ‘planted out’ would qualify for counting under existing international carbon accounting rules and hence qualify for carbon farming credits.

Since kelp grows naturally on submerged rocky outcrops, one measure of suitability for kelp farming is the length of a country’s coastline. On this measure New Zealand, with the ninth longest coastline in the world[iv], looks like it might be a promising candidate.

Estimating a possible upper limit to the potential planting area for kelp is problematic. With a coastal length for New Zealand of 15,000 plus kms, and assuming that kelp might typically grow in a narrow margin out to 30-60 meters offshore, the upper limit for coastal planting is possibly in the order of 45-90,000 hectares. Even assuming Hurliman and Zucker’s figure for the sequestration efficiency of kelp over pine as being a multiple of 20, the total upper sequestration limit is probably no more than around 900,000 – 1,800,000 hectares of pine forest equivalent. There are probably too many assumptions built into this figure for it to be very useful, but given that the Productivity Commission is calling for new plantation forests totalling in the range of 1.3-2.8 million hectares, it does look as if kelp could take up a sizeable portion of the whole and might therefore be a useful adjunct to land-based forests.

There is an obvious objection of course. The prospect of converting sizeable areas of the New Zealand coastline to kelp farming is probably a markedly less attractive idea even than covering 47% of New Zealand’s land area with pine trees. No doubt a careful balance between land-based pine trees and ocean-based kelp farming would need to be struck bearing in mind landscape, beachscape and environmental issues. Perhaps what this discussion best illustrates is the wisdom of reducing gross carbon emissions at source wherever possible, rather than seeking to rely to an undue extent on sequestering carbon.

A large pool of water

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New Zealand Giant or Bladder Kelp: Macrocystis pyrifera.
Image by Shannon DeVaney in

New Zealand research into kelp sequestration

Research in New Zealand into kelp sequestration is at a relatively early stage but interest in seaweed farming is developing and a number of researchers have been active in the field.

Associate Professor Dr Nick Shears (Director of the Leigh Marine Laboratory and President of the New Zealand Marine Sciences Society) is working with postdoctoral student Caitlin Blain on research into the role of kelp forests in carbon sequestration and pH buffering.

Dr Wendy Nelson, principal scientist at NIWA and a researcher at Auckland University, is co-author of an award winning paper on ‘Carbon dioxide mitigation potential of seaweed aquaculture beds (SABs)’. This paper appeared in the Journal of Applied Phycology, Issue 5, Volume 29, October 2017.

Dr Mike Packer, Senior Research Scientist in Algal Biotechnology at the Cawthron Institute, has been leading work on biomass generation by algae as a means to mitigate GHG emissions. See the link at Biomass_Gener-ation_as_a_Tool_for_Greenhouse_Gas_Mitigation_with_Reference_to_New_Zealand_Energy_Strategy_andPolicy/.

Popular interest in the potential of seaweed

Popular interest in seaweed farming is also picking up. On Saturday 12 October Dr Marjan Van Den Belt was interviewed by National Radio’s Kim Hill on seaweed farming, carbon sequestration, environmental and economic aspects and the need for government policy in this area. The interview is available as a podcast at

Marjan is a strategic partner at the sustainability consulting firm Ki Uta Ki Tai (from the mountains to the sea) at and the convener of seaweed collective ReGen Sea. This collective works to promote the role of seaweed in a regenerative economy. Their website is at

Commercial interest in seaweed in New Zealand

Finally, for examples of how commercial interest in seaweed in New Zealand has been developing, three firms are of particular interest.

Based in Paeroa in the Waikato, Agrisea have been manufacturing macro-algae concentrates and bioactive extractions for use in soil, plant, animal and human health applications since 1996. Their website is at

Pacific Harvest on Auckland’s North Shore manufacture and export a wide variety of seaweed-based products including agar, furikake, kelp seasonings, kombu, wakame and karengo. Their website is at

Roger and Nicki Beattie are innovative farmers based on the Banks Peninsula who have been developing food grade kelp under the brand name Valére, and kelp for agricultural and horticultural uses under the brand name Zelp. The Beatties have pioneered sustainable harvesting of Giant Kelp (Macrocsystis pyrifera) in a bay on the Banks Peninsula and they dry the kelp at their farm in Lansdowne Valley. Their website is at

A small boat in a body of water with a mountain in the background

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Macrocystis pyrifera (Giant kelp) being farmed on the Banks Peninsula
A close up of a lush green field

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Giant Kelp drying at Roger and Nikki Beattie’s Lansdowne Farm in Canterbury

For a short, inspirational video on the Beattie’s approach to regenerative farming that features the farming of a wild sheep breed from the Chathams, weka, blue pearls and kelp, see the link at


Kelp farming in New Zealand has an obvious future as a macro-algae concentrate for soil and plant health, as an ingredient in various specialty food products and additives, as cattle feed and for the top dressing of pasture. Whether it can ever be farmed in sufficient quantity to act as a useful adjunct to carbon sequestration efforts on land remains to be seen. In her interview with Kim Hill on National Radio recently (12 October), Dr Marjan Van Den Belt mentioned a back of the envelop calculation that apparently showed that if a way could be found to grow kelp on offshore floating platforms in New Zealand’s EEZ, the amount of kelp required to offset ALL of New Zealand’s greenhouse gas emissions would take up a mere 2% of our EEZ.

This sounds very doable, until we remember that the area of our EEZ is 4 million sq kms. 2% of this is a massive 80,000 sq kms, which implies a series of extraordinarily large floating arrays and an engineering challenge of overwhelming complexity and cost (the largest ship currently afloat is a floating liquified natural gas tanker, the FLNG Prelude, which is 1600 feet long and 243 feet wide). Unless these giant kelp floating arrays were somehow built out of waste plastic engineered to be semi-submersible, the carbon emissions cost involved in building a sufficient array of steel kelp platforms would probably be self-defeating.

An alternative might be to think of concentrating and farming the kelp, or alternatively some other species of a free-floating planktonic seaweed, to form a kind of New Zealand mini-Sargasso Sea[v] in one of our ocean gyres (an area of our oceans that is effectively contained by circulating ocean currents). The South Pacific gyre is too large to be considered, but there is a clockwise circulating gyre in the Ross Sea, for example, that might conceivably be made to serve such a purpose. The waters of the Ross Sea are nutrient rich as a result of the upwelling of cold water from the depths. The area of the Ross Sea gyre is not known with any accuracy but it is probably of the order of 2-3 million sq kms[vi], which puts it into the right range for consideration as a naturally contained but artificially induced, macro algae-based, planktonic carbon sequestration system.[vii]


End notes:

[i] [i]New Zealand Productivity Commission (August 2018). Low-emissions economy: extract from the foreword to the Final Report. Available from

[ii] The primary unit of trade in the Emissions Trading Scheme is the New Zealand Unit (NZU), also called a carbon credit. One NZU represents 1 tonne of carbon dioxide (or the equivalent for other greenhouse gases). Entities that remove greenhouses gases, like those in forestry, can earn units from the government, which they can sell to companies that emit.

[iii] Productivity Commission Finding F11.14.

[iv] The length of the New Zealand coastline is listed in the CIA World Factbook as 15,134 kms. This gives New Zealand a longer coastline than either China or India, and greater than the UK or France. The length of the US coastline is only a little greater than NZ’s. Japan and Australia have significantly longer coastlines than New Zealand, as does Indonesia.

[v] The Sargasso Sea is located in the Northern Atlantic Subtropical Gyre. It is roughly ellipsoid in shape and has an estimated surface area of 11 million sq kms (nearly 3 times the area of New Zealand’s EEZ). The Sargasso Sea derives its name from a seaweed called Sargassum, a genus of brown macroalgae which is planktonic (free floating).

[vi] The area of the Antarctic continent is usually given as 14 million sq kms. The Ross Sea gyre looks like it is probably of the order of one quarter to one fifth of this in area.

[vii]The potential impact of any such initiative on sustainable fisheries and other ecosystems would need to be considered in terms of New Zealand’s responsibilities as a signatory of both the Antarctic Treaty and the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR). Presumably none of the signatories to either of these Treaties would have had in mind possible future carbon sequestration requirements at the time these Treaties were originally negotiated (1959 and 1982 respectively).  

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