My First Interview with Seaweed
- virginiamtorrejon
- 6 jun
- 11 Min. de lectura
Actualizado: 11 jun
I wanted to meet Ulva fenestrata, Chondrus crispus and Sargassum muticum, three of the most emblematic species of seaweed found along our coastlines.
Often dismissed as a nuisance or waste, seaweeds (or macroalgae) plays a vital role in marine ecosystems. They absorb carbon dioxide, release oxygen, help counteract ocean acidification, reduce coastal erosion and shelter fish, molluscs and crustaceans. More recently, they are inspiring the development of new materials that one day may replace conventional plastics, fertilisers and fuel. And they do all this without freshwater, pesticides and arable land.
We met at low tide, at the Plymouth University Marine Station, during the lunch break of the course Collecting & Identifying Seaweed, led by Christine Maggs, Juliet Brodie, Jason Hall-Spencer, Francis and Anne Bunker.
Ulva arrived first, bright and spontaneous, her fronds dancing in the breeze like cellophane. Chondrus emerged calmly, adjusting her blades with elegance. Sargassum arrived last, floating on a current from a distant sea, with her golden vesicles worn like jewellery.
The day was sunny, the sea calm and a few seagulls were flying above us. In the distance, a church bell chimed across the harbour.
VIRGINIA
Ulva, Chondrus, Sargassum, thank you so much for being here. I know you do not accept many interviews.
CHONDRUS (with serene dignity and a calm voice)
That is true, Virginia. Most humans never really ask.
SARGASSUM (adjusting one of her bladders like a brooch)
True.
ULVA (smiling candidly, her fronds swaying energetically)
Thank you for having us! This is my first interview ever.
VIRGINIA
Well, first of all, what exactly are you? Are you marine plants?
CHONDRUS (adjusting her fronds, if she had glasses, she would be adjusting them now)
We photosynthesise, yes, we turn sunlight into chemical energy. But our evolutionary paths diverged from those of land plants hundreds of millions of years ago.
We lack roots, stems and, sadly, flowers. We also normally lack something land plants share: a vascular system (their internal plumbing system). We absorb nutrients directly from the water.
ULVA
We all have the same needs to survive: capture light, a good posture, grow, reproduce... but we got there in different ways. I guess we look like plants… the way dolphins look like fish? Hmm, not sure if that is the best analogy.
SARGASSUM
Still, Ulva’s people, the green seaweeds, are more closely related to plants. But Chondrus and I come from very different evolutionary lines.
Editor’s note:
Seaweeds may look like underwater plants, but most are not part of the plant kingdom. Green algae are the exception. They belong to the same evolutionary group as land plants, Viridiplantae. Red and brown algae, however, belong to different evolutionary branches. Unlike land plants, seaweeds have no vascular system, no xylem or phloem.
VIRGINIA
I see. So, you are not closely related to each other?
ULVA
We are called ‘seaweed’ or ‘macroalgae’, as if we were a single tribe. But we are not. In some classifications, some of us are not even in the same kingdom.
CHONDRUS (nodding)
Ulva belongs to the phylum of Chlorophyta (green algae) phylum, and I belong to Rhodophyta (red algae).
SARGASSUM
And I am a brown alga (Phaeophyceae), a completely separate evolutionary lineage that evolved similar traits independently.
ULVA (with a wink)
You humans do love your labels. But we are not one family. We are what happens when life solves the same problems in different ways.
Editor’s note:
The term algae includes both microalgae (tiny, often single-celled organisms) and macroalgae (seaweeds, larger and multicellular). Seaweed is not a formal scientific category, but a general term for aquatic organisms that photosynthesise. Seaweeds fall into three major groups:
Chlorophyta (green algae). These are the closest relatives of land plants. They contain the pigments chlorophyll a and b, giving them a bright green colour.
Rhodophyta (red algae). They contain chlorophyll a and phycoerythrin, which gives them their red colour and allows them to thrive in deeper waters.
Phaeophyceae (brown algae). These contain chlorophyll a, c and fucoxanthin, which gives them a brownish hue.
These groups are polyphyletic, as Ulva mentioned, they do not form a single branch of life. Their similarities (photosynthesis, flexible bodies, holdfasts) are examples of convergent evolution, not kinship. They evolved similar characteristics because they evolved in similar environments.
VIRGINIA
Fascinating. Could you tell me a bit more about your evolutionary history?
CHONDRUS
Before our kind existed, Earth was a different world, a hostile world. There was no oxygen in the air, no animals, no plants. Only microbes, mostly bacteria and archaea, living in the oceans. Life was almost invisible (she pauses here).
Then, over a billion years ago, something amazing happened. A eukaryote cell (a cell with a nucleus) engulfed a photosynthetic bacterium, a cyanobacterium. But instead of digesting it, it kept it. They formed a partnership and the cyanobacterium became what humans now call a chloroplast, the structure where photosynthesis takes place. So, that was the beginning of photosynthetic eukaryotes and the green and red lineages, my family and hers (she glances toward Ulva).
Editor’s note:
This event is known as primary endosymbiosis, a key moment in evolutionary history. It gave rise to the first photosynthetic eukaryotes, such as green and red algae. This occurred around 2 billion years ago, over a billion years before the first animals appeared and more than 1.5 billion years before modern humans evolved (only around 300,000 years ago).
ULVA
Exactly! We carry the original chloroplasts (her tone is proud). You could say we are the great-great-grandmothers of trees. Some of us left the sea and became land plants. I stayed. Someone had to.
CHONDRUS
My red lineage and Ulva’s diverged soon after the first chloroplast appeared.
SARGASSUM
And then came us, the remix generation. Some eukaryotes engulfed an entire algae, not a bacterium. That is how we got our chloroplasts. Kind of second-hand.
Editor’s note:
This is called secondary endosymbiosis. A eukaryotic host cell engulfed another photosynthetic eukaryote (like green or red alga) and incorporated it. This event gave rise to new photosynthetic groups, like the brown algae, which belong to the group Ochrophyta.
(I know, these Latin names might be a bit mouthful. But someone reading this might want to look them up).
CHONDRUS
So, Virginia, while your species appeared only a few hundred thousand years ago, we have been shaping the world for over a billion.
SARGASSUM
We were turning sunlight into oxygen long before you took your first breath, darling.
VIRGINIA (after a thoughtful pause)
After all you have been through, mass extinctions, drifting continents and climate shifts, how do you see yourselves now? What have you become?
ULVA
Maybe it is better if we describe not ourselves, but each other (they all laugh). I will start. Sorry, Sargassum, I am starting with you. She is a wanderer, a bohemian, following the currents. And sometimes misunderstood.
SARGASSUM (playfully offended)
I am called invasive… Excuse you?! Have you looked at how you humans spread across the planet, sweetheart? You are everywhere! But yes, It is true, I drift, I go where the currents take me. And lately, the currents are warmer, richer in nutrients, and more chaotic. I bloom across oceans and I have a terrible reputation. I also tend to absorb heavy metals, famously arsenic.
Editor’s note: On a global scale, two major threats to biodiversity are habitat destruction and the spread of invasive species. Some seaweed species, especially those introduced beyond their native habitats, are considered invasive.
Sargassum muticum, for example, is native to the northwestern Pacific but has spread to Europe and North America. While it plays an important role in its native ecosystems, in new regions, it can outcompete local species and alter habitats. Climate change and human activity often accelerate this spread.
Ulva is widely studied as a bioindicator of coastal eutrophication. Its rapid growth in nutrient-rich waters can lead to large blooms, also known as ‘green tides’ especially near agricultural or urban runoff areas.
ULVA
Chondrus, on the other hand, it is very calm.
CHONDRUS
After so many years I have learned a lot about myself. My cell walls contain carrageenan, a valuable polysaccharide used in food and cosmetics. And I grow slowly, but with purpose. And Sargassum, you forgot to mention your cell walls contain alginate, another important gelling agent!
SARGASSUM
Yes, yes, true. And I want to add we are changing. We are adapting. The waters are not what they were (they all nod quietly and there is a moment of silence).
ULVA (trying to lighten the moment)
All these years,… only to end up being called sea lettuce.
CHONDRUS
And I, Irish Moss.
SARGASSUM (dryly)
I like my Spanish version, Sargazo. It has the flair of El Zorro, don't you think so? (she says it with a dreamy, sarcastic look)
(Ulva giggles. Chondrus moves her main frond with the algal equivalent of an amused headshake)
VIRGINIA
May I ask something a little more intimate? How do you reproduce?
CHONDRUS
Let me tell you how it works in my family, through three generations.
My grandmother was a quiet but determined female gametophyte, an individual with a single set of chromosomes (haploid, n). She had a carpogonium, her reproductive organ. My grandfather, a male gametophyte, released spermatia, tiny male cells without flagella. He was a subtle guy, no chase, no big gestures. He just released spermatia into the sea and hoped for the best. These spermatia drifted, found my grandmother and fertilisation happened.
As a result, a zygote developed directly on her body and grew into something called carposporophyte (diploid, 2n). Something like a reproductive backpack that clones children. So, this carposporophyte produced carpospores (diploid spores, 2n) through mitosis, which means there was no reshuffling, just identical copies. One of those carpospores became my mother. She landed on a rock, grew and became a tetrasporophyte, a diploid seaweed. When she matured, she carried out meiosis, creating four tetraspores (haploid, n), each with half her DNA .
One of those tetraspores became me, a female gametophyte again, like my grandmother. And one day, if I am ready I will begin the cycle again
Editor’s note:
A haploid (n) cell carries a single set of chromosomes, like a gamete, ready to meet its other half. A diploid (2n) cell holds both sets, one from each parent, like you and me.
In mitosis, a cell makes an identical copy of itself and the genetic material stays the same. Meiosis, on the other hand, is a shuffle, the cell splits and mixes its genetic information, halving the DNA load to create diversity.
Red seaweed moves through these phases like seasons:
A male gametophyte (n) fertilises a female gametophyte (haploid) and a zygote forms (2n).
From the zygote, the carposporophyte (2n) develops and produces diploid spores (carpospores, 2n) by mitosis.
These spores develop a new individal, a tetrasporophyte (2n), which produces four haploid spores (tetraspores, n) by meiosis.
VIRGINIA
So, Chondrus, are you sexual or asexual?
CHONDRUS
We alternate. We have our phases.
We have a so-called triphasic life cycle, unique to red algae like me. Three generations: haploid gametophytes, diploid carposporophyte and diploid tetrasporophyte. It is a blend of sexual and asexual stages, each with its own role.
VIRGINIA
I see, so one generation produces gametes and the other two produce spores?
CHONDRUS
Exactly.
ULVA
I alternate too. Unlike Chondrus, I follow a biphasic life cycle. My gametophyte (haploid phase) and sporophyte (diploid phase) look the same. You wouldn’t be able to tell us apart visually. This is called an isomorphic alternation of generations.
However, my sperm do swim, unlike Chondrus’. They have two flagella. After fertilisation, the diploid zygote grows into a sporophyte, which also looks like me. This sporophyte undergoes meiosis, producing zoospores, flagellated haploid spores that swim and settle to become new gametophytes.
Also, fun fact: in some Ulva species, gametophytes are not male and female, but instead exist as two mating types, positive (+) and negative (-), which determines compatibility for fertilisation. So, reproduction in nature does not always rely on binary opposites, but can emerge from the interaction of equal and non-gendered partners. The two gametes look the same, yet life begins when their subtle and non-visible difference aligns.
Also, both the haploid (gametophyte) and diploid (sporophyte) phases can reproduce asexually, forming new individuals without fertilisation.
SARGASSUM
I do not alternate generations. I am diplontic. My life cycle is dominated by the diploid phase. The haploid stage is highly reduced, confined to gametes only.
When the time is right, I form receptacles at the tips of my branches. Inside them are oogonia and antheridia: eggs and sperm. The male gametes are flagellated, swimming toward the egg. Fertilisation happens right there and the new diploid zygote grows immediately into a young Sargassum. No alternation. No fuss.
But when I am out floating freely in the ocean, I can also reproduce asexually by fragmentation. A broken fragment of me can regenerate into a fully functional new individual.
VIRGINIA
Wait… your sexual reproduction sounds almost human. I mean: diploid body, gametes, fertilisation, zygote. Is it basically like us?
SARGASSUM
Do not get too excited, Virginia. I do not have lovers. We release gametes that fuse to form a zygote and then the cycle starts again. No candlelight, no courtship. In fact, most of us do not need a partner. Many Sargassum species, like myself, are monoicous: we produce both eggs and sperm on the same body. Efficient, right? Though some of us, are dioicous, strictly one sex per individual. Either way, the job gets done.
So, no we are not like humans in that sense. And I do not envy the drama (she smiles slightly condescending).
ULVA (teasing)
She says that now... wait until the next tide comes and no one is releasing.
SARGASSUM
I will grow myself. Thank you very much.
Editor’s note:
German philosopher Arthur Schopenhauer famously argued that love is merely a call of nature, an illusion designed to ensure the reproduction of the species. In his view, desire tricks us to perpetuate life. Seaweeds, it seems, do not have this deception.
Perhaps he was only partially right.
VIRGINIA
So let me see if I got this. Chondrus, you have a triphasic life cycle. Ulva, you have a biphasic isomorphic life cycle. And Sargassum, you stay diploid your whole visible life.
CHONDRUS
Yes. But I want to clarify that reproduction for us is less about who and more about when and how. We think in terms of rhythms, of going with the flow of the ocean.
And yet, somehow, we make it work. Triphasic, biphasic, diplontic, asexual... not because one is better, but because each suits our environment, our history, our body, and our circumstances.
VIRGINIA
That is very comforting.
ULVA
Well, we have had over a billion years to evolve better habits.
VIRGINIA
So, no affection? Choice? Love?
CHONDRUS
Not like yours. We do not possess a nervous system, emotions, cultural patterns, or decision-making faculties like yours. There is no affection in the human sense.
But we know timing, flow, chemistry, proximity. We respond to the sea: salinity, light, nutrients, and temperature. These activate genes that tell us when to release gametes.
(pauses a moment)
In the end, what you call love… we experience it as timing. Maybe that is our version of desire. A carpogonium waits. A spermatium drifts in at just the right moment. Chemical signals align and life continues. It is a kind of dance.
VIRGINIA
There is something beautiful in that, that is for sure.
CHONDRUS
Yes, not because we feel it. But because we have done it for a billion years. And it still works.
SARGASSUM
When the current is right and everyone’s releasing, who needs affection?
VIRGINIA
We could be discussing this for hours. These topics are fascinating. And difficult. For humans, it is difficult to understand your cycles. But tell me now, what role do you hope to play in the future of this planet? What would you like humans to understand about you?
ULVA
I want to keep inspiring. Not just as food or future packaging, but as a reminder that beauty can be simple. I would hope humans remember we are not waste.
CHONDRUS
I would like to be understood. Fully. Not just extracted and processed. We hold complexity, in our molecules and our history. I would love humans to see the value in slow growth and quiet presence.
SARGASSUM
I want my reputation back.
VIRGINIA
Thank you very much for your time and your patience, ladies.
CHONDRUS
Anytime, Virginia, it was a real pleasure.
ULVA
Do not forget to write our names properly, please! Ulva fenestrata. Chondrus crispus. Sargassum muticum. The first word capitalised. Second lowercase. In italics.
Editor’s note:
The tradition of using binomial nomenclature (genus and species in Latin) was popularised by Carl Linnaeus in the 18th century.
SARGASSUM
See you in the lab. Wear gloves.
Perhaps the future lies not only in new technologies but in learning from ancient ones. Next time you walk by seaweed on the beach, listen to it.
Thank you Christine, Juliet, Jason, Francis and Anne. Most of what I know (and possibly some of what I misunderstood) comes from your course. I am still learning and this interview is part of the process. Please forgive the errors, they belong to the student, not the teachers.
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