Is seaweed a sustainable crop?
You tell me.
In the last newsletter, I talked about seaweeds as a replacement for fashion’s unsustainable raw materials: thirsty cotton, petrochemical polyester and cruel, deforesting, methane-burping leather and wool.
In the end, though, there is nothing inherently unsustainable about cotton. It’s a bio-based, compostable material. Adds to biodiversity. Even takes up carbon! It’s only because of a lack of concern for environmental boundaries that cotton farming drained the world’s fourth-largest lake.
If I plant a palm tree in my permaculture forest garden and harvest some palm oil from it, that’s sustainable. And if I chop too many mangroves, float my lines with styrofoam and douse my seaweeds in urea, that’s unsustainable.
It’s not what you grow, it’s how you grow it.
So is seaweed aquaculture, as it is practiced today, sustainable? For tropical seaweeds, at least, that statement comes with caveats.
*** On 6-7 September, Seagriculture US will take place in Portland, Maine. I will also be in attendance. You can still buy tickets - here. ***
No fertilizer
It is often said that, unlike land crops, seaweeds do not need fertilizer. That’s something of a sophism though. Land crops don’t need fertilizer either. They will grow. Just not as big.
What makes land farmers use synthetic fertilizers is an economic logic of producing more for profit or survival. After a few great years of intensive farming, there is no way back; the soil is depleted, the banks want their money back: you are now forced to use fertilizer.
A similar logic has been playing out in seaweeds. While it is important to keep in mind that the majority of seaweed cultivation does not rely on fertilizers (the amount of fertilizer use in China remains a bit of a black box), we should acknowledge that in some places, fertilizer usage is rife.
In Tawi-Tawi province, which grows a quarter of all seaweeds in the Philippines, 83 out of 100 farmers surveyed used synthetic fertilizers. In South Africa, abalone farms use fertilizer to improve the growth of the Ulva they feed their abalone. And in a survey of Indonesian Gracilaria pond farmers, all used inorganic fertilizers, and four different types of pesticides were used.
No fresh water
Seaweeds don’t need fresh water to grow. That is certainly true. But they do need fresh water to process.
For example, alginate factories' water requirements can range from 1000 - 1500 liter per kg of final product. Carrageenan is similarly water-intensive, agar needs around 600 liter. A closed-loop setup is certainly possible, and some producers barely draw any freshwater from the environment, but this is far from a guarantee.
Plastic pollution
Few people will deny that plastic pollution is an issue in mariculture. To their credit, South Korea has recently banned the use of the worst offenders, polystyrene buoys that disintegrate very quickly. But Styrofoam use is still common in the Philippines and Indonesia.
Used plastic bottles are seen as the more sustainable alternative to float lines in these lower middle income countries, since they’ll end up in the ocean anyway if they are not used for seaweed farming. But this cannot be the end point, obviously.
Reducing overfishing through alternative livelihoods
One argument for NGOs to get involved with seaweed cultivation is as an alternative livelihood for fishermen. The argument is clear: if communities earn more with seaweeds, they will have to fish less, allowing fish stocks to recover.
However, there is little evidence that alternative occupations reduce fisher numbers.
As an example, in a survey of 2 seaweed farming villages in Sulawesi, only 3% of fishermen said they had reduced fishing activity as a result of increased seaweed farming. In an ironic twist, they added that because fish are attracted to the seaweed lines, they had bigger catches in less time.
However, in another community, 54% of respondents had given up fishing to become seaweed farmers. Here we could speak of an alternative livelihood. Elsewhere, supplemental livelihood would be a better description.
For those that do give up fishing, the boom and bust cycles of the seaweed market become the next challenge. Whether seaweed cultivation leads to entry or exit from fishing depends to some extent on the world market and prices for seaweed. In places like Solomon Islands and Samoa, this has led communities to completely abandon seaweed mariculture in the past once prices dropped. In Indonesia and the Philippines, people are likely to revert back to fishing temporarily when prices are low.
In some cases, seaweed farming might even provide perverse incentives. For instance, households might reinvest their seaweed winnings into improved fishing gear to catch the last few fish in very degraded areas.
The authors linked above agree that to be successful, interventions involving alternative occupations should be closely tied to more direct forms of resource management, like MPAs or gear restrictions. These measures should in turn be designed *very* carefully to avoid unintended consequences.
Analysis: preventing PR backfire
In future, critics might (rightfully) say: “your biomaterial is supposed to keep microplastics out of the ocean, but farmers use Styrofoam to grow it” or “ your seaweeds are supposed to sequester carbon, but they are grown in abandoned shrimp ponds hacked out of mangrove forest that urgently needs to be restored.”
Sustainability is a big part of the story for seaweed startups. With very limited means to oversee the supply chain, startups relying on tropical seaweeds should take an interest in limiting future reputational fallout.
Trying to stamp out unsustainable practices is challenging from a distance, to say the least. In a fragmented and opaque supply chain, few suppliers are committed to sustainability.
New brokers across the tropics are slowly emerging to increase data, encourage sustainable practices and multiply producer-buyer connections. But for now, it remains a real challenge to build up a transparent supply chain.
Conclusion: trade-offs are inevitable
This leaves us with one option: acknowledge that the tropical seaweed supply chain also has its ugly sides. And while problems with plastic pollution and fertilizer can be fixed, it would be silly to imagine that a future seaweed industry at scale in Europe or North America would only have positive social and environmental outcomes.
As the summary of the MacroFuels project reads:
Seaweed cultivation at large-scale will alter many of the physical, biological, chemical characteristics of the environment. With proper site selection, many of these changes could be considered positive.
However, as with other types of aquaculture there are risks of negative impacts. Authorities must define the thresholds for acceptable impact to ensure [...] natural resources are managed effectively.
When rifling through the reader comments on a recent article about seaweed mariculture in Alaska, I found the tone very negative and distrustful. After centuries of rapacious capitalism, it’s not difficult to see why many in the general public find it hard to believe in a business that says it will be large-scale and profitable, and yet, not awful. They have heard all those promises before.
To alleviate society’s suspicion, seaweed advocates might have to tone down the cheerleading and, to a degree, play into that existing cynicism.
Trade-offs are inevitable. Humans are ecosystem engineers. Not so much like beavers, furry and benign. More like Pablo Escobar’s hippos; on the one hand, we are murderous fatties that produce more shit than our environment can handle, our lives contingent on the whims of a distant coked-up billionaire; on the other hand, we are also apex predators who can have a beneficial effect on the environment, if kept in check.
It’s always going to be a bit of both.
Great article, thank you!