Biology of the Sea of Decay

The tale of Nausicaä (discussed hereafter considering also the comic version) begins with the ‘Sea of Decay’, a forest filled with miasma, a poisonous gas. Humans must wear gas masks here or else their lungs rot and they die. Even outside the Sea of Decay, if they come into contact with drifting miasma poison, their bodies petrify. As the miasma (this toxic forest) expands, the land where humans can live decreases. This overwhelming feeling of enclosure from the miasma is the undercurrent and the worldview of the story.

The Sea of Decay repels human intrusion while also invading the already scant human habitats. Humans are powerless against the silent yet immense oppression emanated by this poisonous forest. Particularly, there is no solution against the ‘Great Ocean Roar’, a sudden surge of the Sea of Decay that engulfs like a tsunami. Humans could only sit quietly and await their doom.

Alas, if humans were humbly powerless, it would have been better. Human malice turns this into a weapon, trying to use it to annihilate each other. This is done by cultivating creatures of the Sea of Decay and creating mutants. The Sea of Decay was exploited using biological knowledge and techniques. The Sea of Decay, however, turned out to be an entity beyond human comprehension, covering the earth far beyond the range of human plots.

But what exactly is the Sea of Decay? Even within the scope of human knowledge, if we knew more about the Sea of Decay, we might understand Nausicaä’s story more deeply. Hoping for that, let’s consider the structure (formation) and function (workings) of the Sea of Decay from a biological perspective.

First, the primary organisms forming the forest of the Sea of Decay are fungi. Fungi belong to a taxonomic group that includes molds and mushrooms and, as will be mentioned later, are not plants. Fungi work as ‘decomposers’ in both the story and real ecosystems. Decomposers are like custodians of the ecosystem; without them, the ground and seafloor would be filled with carcasses and remains.

Of course, scavenging animals like hyenas and jackals can be considered decomposers, but they can’t consume the remains of the most abundant life form on earth—plants! Only fungi and bacteria can break down plant remains.

The reason trees can grow tall against gravity is due to cellulose (which acts like a tree’s skeleton) and lignin. Animals cannot digest or break down these molecules, but fungi and bacteria can, especially fungi, which are the main decomposers on land.

For example, it’s the ‘decay fungi’ that make deadwood and fallen trees eventually rot. The mushroom is a structure that rises from the mold-like mycelium of decay fungi. It looks like new life is regenerating from a dead tree, hence it’s truly a ‘child of the tree’. It becomes clear that mold and mushrooms are two sides of the same coin, as both are decay fungi. Fungi latch onto animal remains to break them down and also parasitize living insects to grow mushrooms, like the ‘Cordyceps fungus’. The story also depicts fungi growing from the remains of the King Worm and other insects.

In the story, fungi grow like trees to a height of 50 Melte (equivalent to 50 meters), and then a new layer grows on top of this, forming a multi-layered structure. In reality, fungal cell walls are made of a tough material called chitin, the same component as the exoskeletons of insects and crustaceans, so there may be a possibility that they can grow into structures as tall as actual trees.


What’s more interesting is that the fungi in the story turn green as they grow, performing “photosynthesis”. Real fungi do not photosynthesize. Photosynthesis is mainly performed by plants and algae (and cyanobacteria). But, there are “lichens” that are a symbiosis of fungi and algae, living as if they were a single organism. They cling to tree trunks, branches, and exterior walls of buildings, and they are among the strongest organisms that can survive in harsh environments where other life forms cannot grow, such as the Antarctic bedrock or newly born volcanic islands. It wouldn’t be surprising to find them in the Sea of Decay in the story.

Since the fungi in the story perform photosynthesis as they grow, they are producers that can provide for themselves. Yet, their essential role in the Sea of Decay is still as decomposers. The fungi in the Sea of Decay play a role in purifying the soil that humans have polluted with industrial civilization. They decompose pollutants and release toxic by-products as exhaust gases. This is the miasma. Humans are chased by the poisonous gas as a consequence of polluting the soil.

In real ecosystems, there are also decomposers of pollutants. These are mainly bacteria. Fungi are “eukaryotes” like us humans, with nuclei in their cells, whereas bacteria are “prokaryotes” without nuclei in their cells. Without going into detail about these biological differences, bacteria are incredibly diverse and versatile in their functions. Even when man-made pollutants that didn’t exist before are released into the environment, bacteria that can decompose them eventually emerge.

When we say they emerge, it could be that a new species of bacteria capable of decomposing the pollutants is born, or existing bacteria may band together to decompose the pollutants. Decomposing man-made pollutants requires complex reaction processes. It’s difficult for a single species of bacteria to undertake all of this, but if various bacteria with different abilities come together, they can exhibit new capabilities that didn’t exist before.

For instance, there are indications that traditional countermeasures such as removing polluted soil (decontamination) or bringing in non-polluted soil (guest soil) have limited effects against “environmental hormones” (endocrine disruptors), which can have adverse effects on humans and other organisms even in minute amounts. In response to this, some suggest relying on the decomposition performed by bacterial communities in the ecosystem. Bioremediation by microbial communities composed of bacteria and the protozoa that eat them is already being used to repair coastal ecosystems damaged by oil spills from tankers.

Speaking of oil spills, the “Exxon Valdez” accident that occurred in 1989 is considered one of the largest ecological disasters in history. Emergency decontamination was carried out in response, but more than twenty years later, bioremediation is still hoped for. Conversely, it means that the restoration has not yet been completed even after more than twenty years. The story’s setting, where it takes thousands of years for the Sea of Decay to purify polluted lands, weighs heavily on the heart.

By the way, in Japan, too, there was an oil spill from the “Nakhodka” in 1997, and a tragedy occurred where five people died from overwork during the decontamination work. The amount of oil spilled at that time was probably around 6000 tons. The oil spilled from the Exxon Valdez was about 10 million tons, but even this does not make the top 50 in global oil spill accidents. The world is already being polluted with oil.

Not only the sea, but soil and groundwater pollution are also becoming serious. Especially in the 21st century, which is called the “century of water” (century of disputes over water), the pollution of groundwater, a valuable water resource, is a matter of life and death. Tens of millions of people around the world are already suffering from arsenic contamination in well water.


The underground is a special environment with oxygen deficiency or anoxia. Nevertheless, there are microorganisms that can exert their abilities in anoxic conditions (descendants of the “organisms that cannot breathe oxygen” mentioned later). Abilities of microorganisms that have been handed down from the ancient times when there was no oxygen on Earth are now being used to save groundwater. Research and implementation for this purpose is currently underway.

And now, there is radioactive contamination. Chernobyl and Fukushima. Unfortunately, there is no trump card for bioremediation of radioactive materials at the moment. We often hear or read statements or articles about “microorganisms that decompose radioactivity”, but they are probably mistaken. Rather than pointing out other people’s mistakes, as a microbial ecologist, I must do something about it through bioremediation. But I have no move to make.

At this point, the words of the “Monk” in the story resonate with me, “Extinction is inevitable… All suffering is a trial for the rebirth of the world.” In response to this, Nausicaa asserts, “I will not give up.” I must keep fighting too.


The Sea of Decay as a “Cradle of a New Species”

Earlier, I mentioned “bioremediation by a group of microorganisms made up of bacteria and protozoans that eat them.” Protozoans include amoebae and slime molds. Slime molds are more amoebic than fungal, with individual amoeba cells behaving as if they form a colony, which is why they are sometimes called “social amoebae.” The representative example is the yellow slime mold Physarum polycephalum, famous for its maze experiment and the experiment to recreate the metropolitan railway network.

In the story, human malice created a mutant form of slime mold. It escaped from human control and gathered in various places, emitting a strong miasma. Its motivation is the “anxiety” and “fear” towards the short life and death that it has been thrown into. When the slime mold gathers, it forms a huge sphere (fruiting body) and ejects countless spores to continue life. These spores rain down all over the surface of the earth, causing the land where humans live to be lost. To pacify it, insects like the Ohmu and others go to the gathering place of the slime molds and are eaten by them. By being eaten and merging with the slime molds, they try to pacify them.

In this story, what is “eaten” is called a “nursery.” The insects are nurseries for the slime molds. And the slime molds are also nurseries for the fungi. This is because the spores of the fungi that were on the insect bodies germinate and eat the slime molds. In the forests of fungi that are created in this way, insects and slime molds gather again, multiply, and a new Sea of Decay is formed.

This is also true in real ecosystems. Life is connected through a “eat or be eaten” food chain. Leftovers, spillage, discarded shells, feces, and carcasses that have fallen out of the food chain also return to the soil through the work of decomposers and become nutrients (such as nitrogen and phosphorus) for plants and algae, the producers. This is the cycle of life in nature.

In the real world, it is known that what is eaten becomes part of what has eaten it. For example, the green sea slug Elysia chlorotica eats a certain type of algae while stealing its chloroplasts and performing photosynthesis within its own body. Normally, photosynthesis cannot be performed properly with chloroplasts alone, but this sea slug has been reported to steal genes from the algae and incorporate them into its own genome.

Genes are usually passed on “vertically” from parent to child, and from child to grandchild. Despite this fact, in nature, it has been found that they can also be transmitted from individual to individual, even across species barriers. This is called “horizontal gene transfer,” and it has been pointed out that it may have a significant impact on the evolution of organisms, particularly microorganisms.

And, not just horizontal gene transfer, but also evolution in the form of a “chimera” formed by the fusion of multiple species is possible. A chimera or chimaira is an imaginary animal with “a lion’s head, a goat’s body, and a snake’s tail,” and interestingly such a creature exists in reality. It is us.

In fact, a part of our human (eukaryotic) cells, the “mitochondria,” was originally another organism. Going back to ancient times, the primitive Earth was almost anoxic. Thanks to the photosynthesis of cyanobacteria, however, oxygen increased. Still, our eukaryotic ancestor cells could not yet breathe oxygen; rather, oxygen was a poisonous gas. The generation of oxygen by cyanobacteria was the first and greatest environmental pollution in Earth’s history. It is also said that there was a mass extinction event known as the “Oxygen Holocaust” at that time (holocaust means mass slaughter).

With that being said, our ancestors overcame this crisis by incorporating oxygen-breathing bacteria, domesticating them in cells, and eventually making them a part of the cell (mitochondria). The incorporated bacteria were neither digested nor decomposed, and they are still alive as mitochondria. This means that our cells can be said to be chimeras.

Here’s another example. It was mentioned that plants and algae perform photosynthesis, but in fact, a part of the cell called the “chloroplast” is the site of photosynthesis. This, too, was originally a cyanobacterium, another organism that was incorporated into a eukaryotic cell, domesticated, and became a part of the cell (chloroplast). This is also a chimera.

Horizontal gene transfer and eukaryotic cell chimerization are realities, and they overlap well with the image of the Sea of Decay in the story, where “being eaten and eating are the same thing in this world, the entire forest is a single life.” The Sea of Decay also seemed to play a role as a “cradle of a new species” through gene mixing and chimerization.

Perhaps, as the generation of oxygen in ancient Earth and the Oxygen Holocaust were overcome, an evolution could occur to “turn disaster into a blessing” for the toxicity of the miasma of the Sea of Decay. In the story, it is prophesied that when the miasma disappears and the pure air is restored, a new holocaust will occur. Many lives will be lost. The history of evolution has been more a history of extinction.

Yet, the final words of the story, “We must live,” are not just Nausicaä’s words. It is also the determination of the forest, which will become a place for re-evolution and re-re-evolution, and will connect life. It should also be the wish of “this planet” (Earth), which has been entrusted with human destiny.


Regarding the Dignity of Life

Let’s recap the three stages that Nausicaä went through in her understanding of the true nature of the Sea of Decay. First, the initial stage, when she fell into the depths of the Sea of Decay with Asbel. At this point, Nausicaä begins to understand the essence of the Sea of Decay, realizing that it’s “probably born to purify this world”. Nonetheless, she harbors a foreboding of doom akin to original sin, contemplating “what if we are the impurity itself”. At this stage, the Sea of Decay appears like a “natural purification device punishing humans who contaminated the soil”, purifying while exuding miasma.

The second stage is when she sees “where the Sea of Decay ends” with the “Forest People”, namely what lies after the Sea of Decay has purified the land. While the miasma of the Sea of Decay may be a punishment for humans, the Sea itself was restoring the once-beautiful, original nature. But Nausicaä hesitates to enter, believing that present humans are still impure and “shouldn’t contaminate this world”. At this point, both the Forest People and Nausicaä believe there’s a “pure land that only pure humans should enter”, thus trusting in the benevolence of nature.

The third stage is the dialogue with the “Master of the Garden” and the climactic “Master of the Tomb”. Here, the Forest People assist Nausicaä. Except the truth revealed here overturns even the convictions of the Forest People. The Sea of Decay wasn’t a naturally occurring “holy lifeform” but was part of the “World Regeneration Program” by the once polluting and destructive massive industrial civilization. Plants, animals, and humans were all modified to withstand the miasma produced during purification. They couldn’t, however, withstand the pure air after the purification, so they were supposed to be further modified. Moreover, this time, they were supposed to be modified into peaceful humans, free of hatred and conflict.

If we compare this to the human body, the first stage is like suffering from a severe illness due to an unhealthy lifestyle. The pain that accompanies natural healing could be considered as the miasma. The second stage is an image of entering a pure Bodhi state of mind and body, if you learn from the severe illness and adopt moderation and abstinence. Natural healing and self-help effort. If you continue to lead an unhealthy lifestyle, it leads to ruin. The third stage is realizing that everything was designed by someone else, unrelated to natural healing or self-help efforts.

Here, while expressing the utmost respect for Professor Shinya Yamanaka of Kyoto University, who won the 2012 Nobel Prize in Physiology or Medicine for his “iPS cells” (induced pluripotent stem cells), I would like to use an analogy, hoping it won’t be misinterpreted. iPS cells are the “raw material” for regenerating a person’s organs or tissues from their cells. There’s no doubt that thanks to this, the number of lives saved will dramatically increase. Even so, when applying this in medicine, “informed consent” (explanation and agreement) is needed beforehand. There might be people who can’t agree due to various beliefs and creeds, even if explained afterward. Even the most wonderful medical action should prioritize the “dignity of the individual”.

In the story, the Sea of Decay is a device to regenerate clean soil from contaminated soil, and the humans in the story are like clay figures for regenerating pure humans. The third stage is where the Master of the Garden and the Master of the Tomb, playing gods, demand “informed consent” from Nausicaä, who is like a clay figure, in a hindsight manner. “You had an incurable disease, so we regenerated your body from a part of your body cells. As the environment changes, you’ll need to regenerate again, so let us operate, agree”. This is just imposing life.

Nausicaä was stubborn. She was upset about her life being interfered with before she was convinced or agreed, even knowing that doing so would allow her to live longer. Nausicaä felt that the “dignity of life” was violated. Whether to live or perish should be chosen by our own will. And so, she said “no” to the life imposed on her. Nausicaä made her decision not logically after considering it, but simply because she disliked the “nasty smell” of playing with life. Even though the Master of the Tomb logically explained “I’m talking about humans as a species”, Nausicaä made a decision representing all humanity. This was only possible with the belief that the value of rejecting imposed life is shared.

From here on, we would enter a political discussion on “how an individual can represent the whole”, so I would like to conclude my biological argument here. I imagine the thought of the Ohmu “individual and whole, whole and individual” also served as a background to legitimize Nausicaä’s representativeness.

Lastly, I want to state that I wonder if Nausicaä’s decision was not hasty. Rather than deciding “not to shy away from ruin” right now, once the whole picture of the “World Regeneration Program” was understood, there must have been a way to approach it calmly. Life should be that tenacious. What do you, the readers, think?

The Sea of Decay is a being that surpasses human knowledge. Indeed, the Sea of Decay was a purification device created by humans, but through genetic mixing and chimerization in its seedbed, it has become a being that surpasses human knowledge. The source of the tenacity of life as I see it lies here.

(This article was article was written around 2013)

Takeshi Naganuma – Born 1961. Associate Professor at Hiroshima University Graduate School. Specializes in microbial ecology. Explores extremophiles in various remote regions around the world, such as the Arctic, Antarctic, deep sea, and deserts. Author of books like “Deep Water ‘Upwelling’, Plowing the Sea!” and more.

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