Marimo balls
Home » Algal research that has its ups and downs…

Algal research that has its ups and downs…

Every so often you chance upon a scientific study that makes you think “What? That’s new or worthy of study (and publication…)?” I had that reaction when I saw the paper entitled, “Photosynthesis and circadian rhythms regulate the buoyancy of marimo lake balls” by Dora Cano-Ramirez et al.. Marimo balls are spheres of Aegagropila linnaei [a filamentous, multicellular, freshwater green alga]. The ‘phycospheres’ are found in shallow freshwaters such as lakes in Iceland, and – most famously – in Lake Akan in Japan. Although Lake Akan is home to an estimated population of 600 million marimo – some exceeding 30 cm in diameter, globally, marimo are threatened and increasingly rare in nature. Primarily associated with the lake bottom, the balls have been observed to float at the lLake surface. And it’s with which buoyant fact that we begin this Cuttings item.

Marimo balls
Marimo (Aegagropila linnaei) in Lake Akan in Japan. Image: コムケ / Wikipedia

Question: Using your knowledge of plants – and that’s plants that famously photosynthesise releasing lighter-than-water oxygen gas – what would you suggest might account for the observed buoyancy of these balls of algae (which are plant-like enough to photosynthesise as do photo-oxygenic land plants…)? Correct, I’ve read your collective thoughts: One might indeed suggest – assume even – that accumulation of photosynthetically-derived oxygen was the cause of this algal levitation, and leave it there. Case closed. Problem solved. Mystery demystified. And – quelle surprise?! – that is in fact what Cano-Ramirez et al. found: the algal balls rise to the surface of the lake [or, rather, the aquarium in their case] during the day – because of the buoyancy they get from photosynthetically-produced oxygen that is trapped in the algal ‘mat’.*

Understandably, one’s response to this discovery might – with some justification – be to say: So? What did you expect? But, that is to miss the point, and in so doing misunderstand the role of scientific inquiry. Just because one might have guessed that photosynthesis was behind the alga’s ballooning behaviour, doesn’t make it so. You have here an excellent example of: a natural phenomenon, a hypothesis that might explain it, and an experiment carried out whose results ‘failed to disprove the hypothesis’. That is the scientific method in action.

So, unless – and until? – an alternative explanation is proffered, it’s official: it’s oxygenic photosynthesis that make the marimo balls ascend. Are there any ‘practical applications’ of this research? ** I know not. But, what if there aren’t? Is that a problem? Does all science have to have a practical application? Can’t we just acknowledge that this work is a rather nice piece of ‘science in action’? Let us therefore salute those who don’t just accept that what is assumed to be the case is, but choose to test the received wisdom and gather the necessary evidence. In scientia veritas..? Well done, team Cano-Ramirez! ***

[Ed. – in 1921 Lake Akan’s marimo were designated a Natural Monument of Japan, and became a Special Natural Treasure in 1952. Marimo is also the subject and focus of an annual festival by the Ainu people in Hokkaido. During this celebration the marimo is welcomed at the beginning of the festivities and returned to the lake at the end in a sacred ceremony. For more on this fascinating ceremony, see Takashi Irimoto.]

* Although the buoyancy is down to the oxygen, the team also found that this light-induced acquisition of buoyancy is related to circadian rhythms of photosynthesis in the marimo. As they conclude, they’ve identified “a circadian-regulated buoyancy response in an intriguing and little-studied plant”.

** The discovery may have future implications – ‘practical applications’ – for conserving marimo, which, according to the study’s lead author PhD student Dora Cano-Ramirez, are “endangered, being currently found in only half the lakes where they were once spotted”.

*** The big question now is: Are marimo balls in one’s aquarium a better alternative to the absolute ‘must-have’ bedroom/living room accessory of the 1960s/1970s, the lava lamp (whose encapsulated coloured oil exhibits a similar photo-induced buoyancy behaviour … and which also operates in a circadian, albeit light-dark reversed, way…)?

Nigel Chaffey

I am a Botanist and former Senior Lecturer in Botany at Bath Spa University (Bath, near Bristol, UK). As News Editor for the Annals of Botany I contributed the monthly Plant Cuttings column to that august international phytological organ for almost 10 years. I am now a freelance plant science communicator and Visiting Research Fellow at Bath Spa University. I also continue to share my Cuttingsesque items - and appraisals of books with a plant focus - with a plant-curious audience at Botany One. In that guise my main goal is to inform (hopefully, in an educational, and entertaining way) others about plants and plant-people interactions, and thereby improve humankind's botanical literacy. I'm happy to be contacted to discuss potential writing - or talking - projects and opportunities.
[ORCID: 0000-0002-4231-9082]

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