Plant Cuttings

This image entitled “Atomic Cloud Rises Over Nagasaki, Japan” by Charles Levy is in the public domain.

A few weeks back I began what is intended to be a series of posts about plants that are under-appreciated by people (and some botanists…). The first item looked at moss. This time the focus is upon seaweed. OK, seaweed is not strictly a plant – by which is usually meant a member of the plant kingdom, i.e., flowering, and non-flowering plants, ferns and their relatives, and mosses, liverworts and hornworts. But, since it is photosynthetic, it’s sufficiently plant-like to be a legitimate subject for a Plant Cutting.

Seaweeds are a relatively small group – approx. 11,000 species – of algae that are readily visible to the unaided eye, i.e. they are macroscopic. They are most commonly encountered by us at the seashore when they are uncovered by the ocean. Seaweeds range in size from quite small individuals, a few millimetres or centimetres in height to those that can be tens of metres in length (Ole Mouritsen). Their biology and ecology are fascinating, as are their interactions with people. We don’t have space to consider everything about seaweeds in this post, but I hope the topic considered here is sufficiently interesting to encourage you to want to find out more about these remarkable organisms. Unfortunately, I must begin with an apology…

Sorry to be a killjoy – especially so soon into the new year, but it’s time to talk about nuclear war. Although it may be 2024, the time on the Doomsday Clock is ’90 seconds to midnight’. That time is the theoretical point of annihilation, which represents an existential risk to Earth and its people from a range of threats such as climate change and disruptive technologies such as artificial intelligence and new biotechnology, and ‘nuclear threats’ (Will Durham).

Nuclear threats are those posed by armed conflict between countries that have the technology – either proven or presumed – to construct and therefore use nuclear weapons (Thomas Cochran et al.). The concern over such threats is chillingly encapsulated in this paragraph “The last year [2023] was characterized by fraught relations among the world’s great powers, who were engaged in vigorous nuclear modernization programs as the nuclear arms control regime continued to collapse. Within this general context, the contours of a peaceful and sustainable ending of Russia’s war against Ukraine are difficult to discern, and concerns remain about Russia’s possible use of nuclear weapons in this conflict” (John Mecklin).

To that statement – from the Bulletin of the Atomic Scientists – is added the named concern that “Nuclear tensions on the Korean Peninsula set to worsen in 2024“, from The International Campaign to Abolish Nuclear Weapons (ICAN). To which we can add this depressing catalogue of conflicted countries, from the Atlantic Council, “The list of difficult relationships among the world’s nuclear powers is long. These include China and the United States, China and India, Pakistan and India, North Korea and the United States, and Russia and NATO [North Atlantic Treaty Organization] … In the background lurks the hostile relationship between Israel, which has never confirmed nor denied that it possesses nuclear weapons, and Iran, which is reportedly now capable of producing enough fissile material for several nuclear weapons”.

With all of this going on in the background, one’s mind cannot help but be focussed on how we humans would survive such a calamity – if at all(!). So, by way of a crumb of comfort in such bleak times, and should we suffer a nuclear outrage, there’s hope that seaweed may save – some – of the human race. Amongst the many consequences of nuclear war is the concern that “burning cities and forests could emit 150 million tonnes of soot, according to previous research, dimming the sun. Temperatures could drop by 9°C (16°F) and global food production from agriculture could decline 90 per cent in the first year of nuclear winter” (Alex Luhn). Research by Florian Ulrich Jehn et al. (Earth’s Future 12(1) January 2024 e2023EF003710; https://doi.org/10.1029/2023EF003710)* specifically considers this post-apocalyptic issue of ‘sunlight-limitation’ – which, they advise, could also be a consequence of natural events such as “an asteroid/comet impact or an eruption of a large volcano”.

Recognising that sunlight-reduction could decimate agriculture as it is currently practiced – primarily upon land – Jehn et al. propose seaweed, which can grow quickly in a wide range of environmental conditions, as an alternative. To test the feasibility of that proposal they developed a mathematical model to examine the potential growth of Gracilaria tikvahiae (a red seaweed (Matt Doggett)) under conditions of ‘nuclear winter climate’.

They found that the seaweed could not only grew in tropical oceans after a nuclear war, but that such growth would be sufficient to satisfy an equivalent of 45% of the global human food demand within 9–14 months. [Although one imagines there may well be considerable supply chain (Adam Hayes) ‘issues’ to overcome if people at distance from the coastal areas are to be fed, and what about the other 55% of human food demand?]. The main limiting factor Jehn et al. identified is the speed at which new seaweed farms can be built [which may be a function of availability of people to construct and run them in the aftermath of nuclear conflict]. Intriguingly, their results predict that seaweed growth increases with severity of the nuclear war, as more nutrients become available due to increased vertical mixing within the ocean as a result of the global cooling accompanying the reduction in sunlight (Cheryl Harrison et al., AGU Advances 3(4) August 2022 e2021AV000610; https://doi.org/10.1029/2021AV000610).

All things considered, Jehn et al. demonstrate that seaweed has the potential to be a viable resilient food source for ‘abrupt sunlight reduction’ scenarios. However, and as Jeth et al. recognise, “It is likely that successful food production with seaweed in an abrupt sunlight reduction scenario needs a wider variety of species. This means there is a need to model additional species, so that the best species combination for every region can be identified”. [Have you ever seen better justification for grant-funding of a research project?]

But, even if enough seaweed can be produced, will people eat it? Well, given the catastrophe that’s envisaged, you’d probably think any survivors would be grateful to eat anything. However, there’s also considerable precedence for seaweed-consumption by humans, both in the present-day, and in the past. Nowadays, seaweed is widely – and traditionally – eaten, particularly in Asian countries (Thierry Chopin]), e.g. Japan [a red seaweed – known as nori – is the black wrap around sushi]. And, historically, seaweed is a foodstuff that we used to eat more widely and commonly, as reported by Stephen Buckley et al. (Nat Commun 14, 6192 (2023); https://doi.org/10.1038/s41467-023-41671-2).

Buckley et al. examined the remains of food on the teeth of individuals from throughout Europe dated between the Mesolithic and the 7^th –12^th centuries AD [the Middle Ages]. Amongst the vegetation, they found indications of ingestion of freshwater plants (e.g. Nymphaea and Potamogeton spp.), freshwater micro- and macro-algae, and marine seaweeds during that time-frame. Specifically for seaweeds, they found biochemical ‘markers’ – any physical remains of the seaweeds had long since disappeared – within the calculus from teeth of individuals throughout the Neolithic, from Early (approx. 3,700 BC) to Middle – Late Neolithic (3,200–2,800 BC), with one instance from a Portuguese site dated to 6,059–5,849 cal BC in the Mesolithic.

Although seaweed has not been a major part of the European diet for hundreds of years, Karen Hardy – one of the study’s authors – thinks “it would be nice if this study could help to encourage a wider consumption of seaweed in Europe today” [quoted by Chen Ly in her science news item on the work]. In presenting their work for the educated layperson, Karen Hardy & Stephen Buckley conclude that their “results suggest that seaweed was a habitual part of the diet for the time periods we studied, and became a marginal food only relatively recently”. Although largely ‘out of fashion’ as a foodstuff in Europe nowadays, it is noteworthy that the University of York’s press release promoting Buckley et al‘s research tells us that, “by the 18th Century seaweed was considered as famine food”. If atomic Armageddon is visited upon us, and if Jehn et al’s phycological proposals are realised, it may be so again.

Even in the absence of nuclear winter [something which, I’m sure, we all hope for], it’s probably time we gave more attention to seaweeds as a food source**. This was considered by PAJ van Oort et al. (Ecological Modelling 484 (2023) 110486; https://doi.org/10.1016/j.ecolmodel.2023.110486), who concluded that, “Within large uncertainty boundaries it shows seaweeds could contribute up to 2 to 14% of global food supply, a substantial contribution that will only be achieved with unprecedented increases in seaweed production”. Bomb appétit!

* I don’t know if there is such a thing as an award for the ‘most intriguing title of a scientific paper’, but, if there is, Jehn et al. (2024)’s “Seaweed as a Resilient Food Solution After a Nuclear War” should be a contender. And, Alec Luhn should be in the running for the ‘science news headline award’ with, “Seaweed could save a billion people from famine after a nuclear war”.

** Another good reason to look more closely at seaweed farming is provided by Scott Spillias et al. (Nat Sustain 6: 380–390, 2023; https://doi.org/10.1038/s41893-022-01043-y). They see that form of marine aquaculture as a way of reducing the problems associated with expansion of terrestrial agriculture to meet humanity’s growing needs for food and materials because it is “a leading driver of land-use change, exacerbating climate change and biodiversity loss”. Although they do show that global production of seaweed has the potential to reduce environmental impacts of land-based agriculture, “caution is needed to ensure that these challenges are not displaced from the land to the ocean” (Spillias et al., 2023).

Tags: botany, seaweeds, nuclear war, Armageddon, Apocalypse, famine food, calculus, science communication, seaweed farming, dental calculus, aquaculture, The International Campaign to Abolish Nuclear Weapons (ICAN), Bulletin of the Atomic Scientists, NATO (North Atlantic Treaty Organization), Atlantic Council, plant biology, Neolithic, Mesolithic, nori, sushi,