A few weeks ago I was conducting a research in fish pond and observed that every daytime there are floating scum-like filamentous algae in the water surface but they disappear at night. How can this be? Since as far as I know they cannot actively move. Thank you :)
It is possible that the filamentous algae are lifted to the surface by gas bubbles.
There can be a day-night rhythm as you describe if the bubbles are oxygen from supersaturation due to high photosynthesis activity.
What happens during daytime is, oxygen that gets trapped between filaments of algae, moves them to the surface and during night as O2 is not produced, they slowly sink to lower depths, and you don't see them
It is interesting! thank you Prof. Henrik and Chandravadan for your answer. It shed the light on me :)
Anyway, could you give me some suggestion about books or article to deepen my knowledge on it? Thanks!
many algal cells have gas vesicles which allow them to undergo vertical migration in water column as response to light conditions. During night these gas vesicles are filled up due to respiration and CO2, it enhances the surface:volume ratio thereby making the cells more buoyant. As photosynthesis occur during daytime, due to formation of glucose and starch, osmotic pressure changes within the cell that breaks don the gas vesicles due to hydrostatic pressure. This causes the sinking of the cells. This is also an adaptation to photoacclimation.
Very nice explanations. I agree with the first two points. It is important to take into account that besides oxygen production during the day due to photosynthesis another, just as important factor is respiration at night which will consume the O2 and thus lead to the sinking. This respiration occurs not just in bacteria but also in photosynthetic organisms as they use the carbohydrates produced with photosynthesis in the absence of the light energy from the sun and thus essentially become net heterotrophic.
Hi Avik, for some reason your (reasonable) explanation is quite opposite to that (also resonable) of the others. Not being an expert on this subject I'm confused. MB-Y
Hi Menakhem,
His explanation fits also, just a different strategy and not that of the algae in your observation. These are both occurring adaptations used to regulate buoyancy although I feel as if though the 'oxygen getting trapped in the filaments' might be an unforeseen consequence. Not sure though.
Florian makes a good point: there are various strategies and benefits to diurnal migration. Considering also the movement by flagellated algae, if the vertical movement is sufficient, it is possible for them to obtain regenerated nutrients at depth and adequate solar radiation in shallower depths for a fairly sophisticated system--at least that is my understanding as a modeler.
Another possibility is a combination of one of thte mechanisms mentionned, that concentrates the algae during daytime with thermal destratification. During daytime the water heats at the surface leading to stable stratification while during the night the surface cools down and the water column is mixed again, distributing also hte algae more or less evenly over depth.
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