Photosynthesis and circadian rhythms regulate the buoyancy of marimo lake balls

Abstract

Marimo are unusual, attractive and endangered spherical aggregations of the filamentous green macroalga Aegagropila linnaei (Figure 1A-E) [1]. Globally rare, marimo populations persist in cold freshwater lakes in Japan, Iceland and Ukraine. Marimo occupy both the lake bed and rise to the lake surface [2,3]. Here, we show that marimo buoyancy is conferred by bubbles arising from photosynthesis. We find that light-induced acquisition of buoyancy by marimo is circadian-regulated. We identify that there are circadian rhythms of photosynthesis in marimo, which might explain the circadian rhythm of buoyancy in response to light. This identifies a circadian-regulated buoyancy response in an intriguing and little-studied plant.

Plant Cuttings

“…And -quelle surprise?! -that is in fact what Cano-Ramirez et al [1] 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?…”

“…Discarded plastic [1] * is a major source of this planet's pollution ("the action or process of making land, water, air, etc., dirty and not safe or suitable to use" [2] ), and which is worldwide -whether on land or on, and in, the ocean [3; 4; 5] . Seemingly, nowhere on Earth escapes this modern menace -plastics have even been detected at the bottom of the deepest parts of the ocean [6] .…”

“…**** As welcome as this news is my major disappointment with the study was the fact that they didn't take the opportunity to illustrate the article with the 'classic' Maltese cross [23] images of polystyrene particles in polarized light. Apparently, this is the only man-made material that produces that pattern and which can therefore be confused with starch in the light microscope [24; 25] … Image from: Wikimedia Commons v Bread's birth bested by 4400 years Like many of you reading this item I suspect, I was taught that agriculture was 'invented' about 10,000 years ago [1] in the so-called Fertile Crescent [2] , an ancient territory that corresponds to much of the modern-day Middle East [3] . Also, and equally no doubt like many readers, I took that remarkably civilising innovation [4; 5] -when societies adopted more sedentary lifestyles with domestication of cereals and animals -to infer that was also the time when bread ["a kind of food made of flour [commonly from ground grains of cereals such as wheat] or meal that has been mixed with milk or water, made into a dough or batter, with or without yeast or other leavening agent, and baked" 6 ] was created and became such a big part of mankind's daily existence.…”

“…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 [1] . Marimo balls are spheres of Aegagropila linnaei [a filamentous, multicellular, freshwater green alga 2; 3 ].…”

Marimo machines: oscillators, biosensors and actuators

“…Other researchers [16] have studied the natural characteristics of Marimo; in particular, its ability to rise and sink in water, which was found to result from generation of oxygen via photosynthesis. Bubbles are formed on the surface of, and at shallow depths within, the Marimo when they are provided with illumination: it is assumed that the filamentous nature of the alga both provides numerous nucleation sites and creates a mesh through which it is difficult for the oxygen bubbles to dissipate.…”