Seaweed - In Depth


John Cunningham

Most residents of the North Atlantic region are aware that our coasts are awash with seaweed and when encountered on beaches, best avoided by all but dogs and the most enthusiastic horticulturalists.

Fewer still will have given it a second thought and some may even be aware of the functions these mysterious plant-like organisms perform in our seas or the uses to which they can be put. Increasing numbers of people however are becoming enlightened to their wonders and wondrous potential. A Fibonacci fractal of complexity and promise which is only now being unraveled. The term seaweed falls far short of adequately describing the sophistication of what is one of the key biological systems on the planet and one which glues the biosphere together, sustaining all life in the oceans, uniting it with all life on earth and playing a critical role in the regulation of global climate. In this series of articles, the term seaweed shall be used to denote the collective qualities of marine algal biomes, however species shall be named when specific qualities are being referenced.


Whilst seaweed has been studied for centuries, the secrets and seemingly endless possibilities of the estimated 20,000+ species of marine algae are currently being unlocked as never before. Through the application of techniques such as gene sequencing and spectroscopy, extracts and derivatives are being identified, revealing a bewildering array of uses applications and opportunities. The myth that seaweeds are a universal elixir for all ills is perhaps not as some have suggested, a myth. Over a quarter of their composition is mineral, with many of their most useful chemical creations manufactured nowhere else on the planet. The rapid increase in our understanding of the function and potential of our vast underwater forests and the biological soup of floating phytoplankton comes just in time as ecological imperatives force us to look for alternative and sustainable means of meeting the needs of an ever-expanding global population. Seaweed promises a new generation of foods, fuels, plastics, medicines and medical products, biologically active nutraceutical cosmetics and as yet unidentified potential and the race is on to devise ways to maximize production and optimize the processing of a wide range of sea vegetable species to realize their revolutionary qualities as quickly as possible.

Algae are found all over the planet and perform many complex biological functions however by far the most biologically significant are the marine algae.

Seaweeds fall into three broad categories of Red (Rhodophyta) comprised of 7000 species, Brown (Phaeophyta), 2000 species and Green (Chlorophyta) at potentially 7000 species. Scientists now believe there may be up to 20,000 species of seaweed, with much of the species differentiation made possible through developments in gene sequencing, though too recent to have been taxonomically ordered. A common complaint amongst students of seaweed is that textbooks are out of date by the time they’re in print.

Floating or fixed, micro or macro, marine algae play a critical role in feeding and regulating ocean ecosystems and algae are the very foundation of the marine biosphere. Excluding the tiny amount of life created by chemosynthesis in deep ocean hydrothermal vents, seaweeds are the basis of the whole multi-trophic, multi-faceted, marine food chain and far beyond. They play a critical role in the formation of clouds and therefore regulate the weather across the planet and remove vast quantities of fossil carbon dioxide from both air and sea, reducing the effects of Climate Change and Ocean Acidification. 

JONAA©John Cunningham

JONAA©John Cunningham

Multicellular marine algae are the oldest living organisms ever detected on earth and were the heart of revolution of life on the planet. Cyanobacteria developed into multicellular photosynthesizing organisms some 2.3 million years before present (mybp) when they began to use Chlorophyl to photosynthesize, converting the energy of the sun into polysaccharides (complex sugars) and a key byproduct: Oxygen. They were so successful in this that they precipitated the Great Oxygenation Event, 200 million years later which changed the chemical composition of the oceans and subsequently the atmosphere, transforming the anoxic, toxic soup, saturated with noxious sulfurous gasses, to its current hyper-oxygenated state. Green algae, as they had then become, are responsible for all life on the planet. Nothing less.

Through photosynthesis, the oxygen they produced led to the formation of an Ozone sunscreen and chlorophyta. Green algae made a leap out of the ocean onto the land and made it green, mothering all flora and subsequently fauna on earth. Some of the earliest evidence of seaweed in the fossil record is the taint of chlorophyll as the pigment in Green Marble, laid down 330 million years ago in the Carboniferous period as limestone prior to its metamorphosis.

The more seaweeds are studied, the more their incredibly complexity is revealed. Seemingly identical species, collected in close proximity, are being discovered to highly differentiated, their differences only revealed through sophisticated analysis in the laboratory. As biological classification becomes more complicated, scientists are coming to terms with the fact that the world of phycology will never be the same. 

According to Prof John Bolton, Professor of Biological Science at the University of Cape Town, “Things are still sorting themselves out following the DNA sequencing revolution. There are many more different groups of microscopic marine life than anyone thought, and the old idea of five Kingdoms is still clung to (as it’s easy) but it does not fit the new data. People don't like name changes. They associate the name too closely with the thing itself."

In the cold nutrient rich waters of the North Atlantic, macro-algae or big seaweeds form marine forests, where a single frond of Sugarkelp (saccharina latissima) can grow up to 4m in length in a mere three months. The depth to which they are to be found is determined by the diminishing penetration of sunlight and light requirements individual species, though mostly occupying the upper 40m of the water column. Professor Bolton goes on to reveal the interesting evolutionary history of seaweeds and the integral role they played in founding life the planet as we know it. “All land plants are an evolutionary offshoot of green algae, so Ulva Lactuca (Sea Lettuce) is evolutionarily more closely related to heather and gorse than it is to brown or red algae. The red algae are one step removed from the green plants (algae and land plants) at this distant scale, whereas the brown algae are extremely distant.”


Seaweed in its natural habitat is unquestionably sexy and slipping through the slate grey membrane of the North Atlantic, ideally in a dry suit, one is admitted to a surreal and enchanted Eden. In stark contrast to adjacent lands, beautiful though brutally hostile, we find ourselves trespassing in a mermaid’s boudoir, a forbidden paradise of life and abundance, swirling in a dreamlike trance and hung with intimate indefinite apparel. Silken frills and delicate lace, shimmering latex and translucent diaphanous satin in reds, greens, and browns, weave harmonically in the dappled light, it’s fronds giving sanctuary and a nursery habitat to a multitude of surreal creatures. This fantasia of color and life exists in a state of continuous animation, choreographed to a silent celestial symphony. In shells, in holes, on legs or swimming freely in her fronds. Fish, mollusks, bivalves, crustaceans, urchins and starfish (echinoderms), sponges, worms, anemones, and a multitude of other life forms create a kaleidoscope of writhing life in this complex and highly diverse community.

It is estimated that 80% of all life on Earth is found in the oceans and 90% of all photosynthesizing life. 

Seaweeds produce 70% of the planet’s oxygen and are responsible for much atmospheric gas exchange with the oceans. They are the oceans Primary Producers fueling the whole marine food web. Using carbon dioxide, sunlight and nutrients, they create biomass at a rate of 6-10 times that of the most productive land based agricultural systems, thereby sustaining life in abundance.

The photosynthesizing surfaces of macro algae are continually in motion, ensuring that they are continually exposed to the sun, flowing freely as contorting fronds or hoisted by bladders of trapped gas elevated towards the surface, their movement ensuring sunlight penetrates beneath the canopy to the plants at lower levels and on the seabed, as with the land based forests we are familiar with. 

Seaweeds will usually attach to a solid substrate such as a rock by an exceptionally strong holdfast, which although having the appearance of a root, plays no role in the uptake of minerals.

Holdfasts demonstrate exceptional adhesive properties, as in the case of Ascophyllum Nodosum, a 1cm diameter anchor can secure a clump of weed 2m in length.



Phytoplankton, the free-floating seaweeds can be microscopic by design or macroscopic, microalgae detached from their substrate and floating off, though continuing to function. The unique and highly desirable qualities of seaweed can largely be attributed to their composition. Broadly speaking they are 25% Protein, 45% Carbohydrate, 4% Fat and 26% Mineral. Their exceptionally high concentrations of minerals are the result of an unparalleled capacity to absorb and accumulate these trace chemicals from the sea by a process known as bioremediation. This unprecedented mineral density gives seaweeds their almost miraculous qualities. Ulva lactuca or Sea Lettuce, as mentioned by Prof Bolton is a true wonder weed credited, in a number of Peer Reviewed scientific papers, as containing exceptionally high levels of plant hormones or stenols. Described as being like steroids for plants, they not only fertilize, but actively promote mineral uptake, boosting growth and yield. They kill harmful algal blooms such as Red Tides and extracts have been found to have antifungal, antiviral and antibacterial (antibiotic) properties which may lead to solutions to antibiotic resistant superbugs and have led to patents for treatment of the Herpes Simplex virus and some cancers. Ulva derivatives can be used to produce an economically competitive biodegradable thermoplastic, capable of performing all the functions for which we currently depend upon indestructible fossil plastics. The world has finally to the dangers of these ubiquitous, highly toxic compounds known to be choking oceans and poisoning the food chain and safe biodegradable alternatives are desperately needed.

With such exciting potential, what does the future hold for our not so humble smelly sludge? Perhaps the question is better reframed as what future might its future hold for ours. Seaweeds represent the least compromised, least exploited components of the biosphere, and retain much of their functionality. 

Our underwater rainforests cannot however be taken for granted as whilst they collectively play a significant role in the regulating global climate, individual species can be highly sensitive to changes in temperature and salinity and many kelp species are known to be migrating northwards as waters warm, specially kelps as they are unable to reproduce in water above 20ºC. The consequences of imbalance in this delicate system of interdependence due to a range of external factors however can be rapid, dire and destructive. The sudden onset of coastal erosion in Nova Scotia (and at other location), resulted from the sudden disappearance of protective kelp beds which had absorbed much of the oceans kinetic energy was linked to the persecution of sea otters. The removal of otters from the ecosystem had led to an explosion of kelp devouring sea urchins and when otter persecution was halted, the kelp quickly reestablished and the vital storm protection grew back.

Native seaweeds can also be threatened by invasive nonnative species, such as Hetrosiphonia Japonica, which has colonized much of the North Atlantic in the last few decades. Invasive species are often less attractive to predators than native species and can outgrow and therefore out compete them. Nonnative seaweeds, along with algal pathogens can be transported around the globe by a range of vectors. Ships ballast water appears to be one of the greatest culprits and the internationalization of the Blue Economy may lead to unforeseen transmission as has happened all too often in Fin fish aquaculture.

Global Seaweed, the organization run by Dr. Claire Gachon of the Scottish Association for Marine Science was recently been awarded a grant of £5m to research and develop a strategy to facilitate the expansion of seaweed aquaculture in developing nations sustainably, through education and regulation, ensuring awareness of the treats posed by pathogens and invasive species.

Regulation from the earliest opportunity, authoritative independent oversight must be agreed at a National, ideally International level and standards and procedures established and enforced.

As we slide with deeper uncertainty into the Anthropocene, it is increasingly clear that history will be no guide to the future and we urgently need to reform our destructive ways or follow the path of the Dodo. It is often observed that in order to control the future, one must first invent it and it is apparent for all to see that the only realistic means we have of securing that future is through remediating existing problems. A global program of extensive open ocean seaweed farming would appear to be the only means at our disposal of simultaneously addressing Climate Change whilst providing unlimited highly nutritious food and useful biomass and this will only be achieved through strict adherence to biosecurity. 

Seaweed however is far too critical a resource to be left to the whims, discretion and tyranny of The Market, indeed to describe it as a resource is to misunderstand its intrinsic value to the rest of the ecosphere. It is truly invaluable and beyond the common trivialities, in the Grand Scheme to which we attribute that accolade. The Market will value seaweed by the ton, whilst failing to recognize the wider economic contribution, let alone the inestimable ecological value of this miracle of nature. What of the value added to the Shellfish Industry, still in business because their stocks had not been killed off by acidification or fish stocks whose numbers are maintained by safe nursery habitats. By releasing Dimethyl Sulphide, seaweeds are integral in the formation of clouds and weather around the planet, helping distribute moisture in regular predictable patterns, sustaining agriculture and settlement.

Humanity has a narrow window of opportunity within which to embrace genuine alternatives to our fatally flawed Modus Operandi. We must and can embrace the narrow range of options available to create a truly circular and sustainable economy upon which all other illusory economies depend. Nature only does circular economies and it is our distortion indeed disruption of this circularity which has created our peril.

During his keynote address to the Arctic Assembly in Reykjavik in 2016, the Secretary General of the U.N. Ban-ki-Moon stated that there was “No Plan B on Climate as there was no Planet B”.

It is imperative that we recognize just how precious seaweed is to our future, to our financial economy and to the vastly more important global ecological economy. In a world dominated by illusory electronic numbers, the value of ecological stability is incalculable. Lose that stability and little else will matter. There will be no economy. 

Are we close to redefining the doom laden epoch of the Anthropocene with a seaweed revolution, or will it be Business as usual until we are ejected from the planet in a self-preserving Gaian reflex against our contempt? Seaweed may even hold the answers to questions, the existence of which we are currently unaware. Researchers at the Georgia Institute of Technology have been using an alginate extract of kelp to boost the storage capacity of Lithium batteries by a factor of 10 and design artist… has conceived a futuristic system of air travel based on algae. © GreenWave

Algal biofuels upon examination however may not fit the conventional model of circularity as there are phases in their cycle when they will contribute CO2 to the atmosphere in both processing and combustion before their carbon is re-sequestrated through photosynthesis. More like an ellipse with a twist - the internationally recognized symbol of absolutus infinitus, the symbol of infinity. 

Seaweed represents a world of impossible complication in microcosm of otherworldly beauty and unimagined promise. Snake Oil it most certainly is not. A ubiquitous elixir? A panacea? A Godsend? Perhaps. It could be the fuel of perpetual motion alluded to in Jules Verne’s “Twenty Thousand Leagues Under the Sea." It will be what we make of it. Should we choose it, should we demand it, our secure future is wrapped in seaweed. 



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