Question concerning photosynteticaly active areas in different algue

[JonasRoman]

we had a discussion and i cannot refind the articles so maybe you can help me.
We are discussing if there is true that macroalgue (caulerpa for instance) is less effective than microalgue in photosyntesis( thus also N o P consumption), due to the fact that some areas such as stem on a macroalgue do not photosyntes (only the leaves) but in microalgue all the surface does.
Is this true?

Thanks in advance
Jonas

 

[Randy Holmes-Farley]

The answer might depend on what you mean by "less effective", which could reasonably be defined many different ways. The exact conditions also likely matter.

Here are three comments, but I've never seen a published study of their photosynthetic efficiency:

1. When I first set up a refugium many years ago, I had several different macroalgae in it. Eventually, microsalgae began to grow on the macroalgae, overrunning it. So in one sense the microlgae was being more effective in those conditions. Then someone suggested to me that iron dosing might help the macroalgae. It did, and I never had that problem again. So later the macroalgae were more effective, but not earlier. So exact conditions matter.

2. Over time, I found that Caulerpa racemosa could outcompete chaetomorpha, suggesting that it could drive nutrients low enough that the Chaeto didn't thrive, although that isn't the only possible explanation. Many others have had similar experiences, suggestion the Caulerpa may be more efficient at reducing nutrients very low that chaetomorpha, which lacks those rootlets.

3. When I grow Caulerpa racemosa in my refugia, it makes a very thick mat, blocking all light. Every bit exposed on the top is bright green and all of the bits on the bottom are much paler, almost white. IME, all parts of the Caulerpa except the little white rootlets can photosynthisize, and the rootlets are not generally blocking much light from photosynthesizing parts when it is allowed to grow into a dense mat.

 

[JonasRoman]

Thanks for nice reflections
The reason of My question is that i followed a discussion somewhere when some claimed that the are significant difference between macroalguerefugium and a turf scrubber in consumption nutrients and that reason should be that microalgues (that are in a turf scrubber) photosyntes on every mm square but macroalgue does not as they are pleomorph in histology.
But i really do not know and cannot find the article where i red this. I know that there is some similar theories why for instance some unwanted species in a carpet Will not thrive if you keeping them low..then you always cut the leaves off and there is less photosyntesis activity in stem than in leaves.
But i am not sure and thus would like to confirm or throw away My theory that there are at least less photosyntetic activity in the stem than in the leaves in a caulerpa.
More input Will make me happy

Jonas

 

[Randy Holmes-Farley]

Walter Addey, when he invented the turf scrubber, believed that turf algae were the most efficient. That has been repeated lots of times, and may be true, but I've not seen any data myself. I doubt the reasons are as simple as the lack of nonphotosynthetic roots.

Here's a recent reference to it the efficiency (or at least, the growth rate):

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0014312

Turf algae (or “algal turfs”) are dense, multi-species assemblages of filamentous benthic algae and cyanobacteria that are typically less than 1 cm in height [15]. Compared to macro algae, turf algae grow faster [16], occupy newly available space faster [17], [18] and are less vulnerable to physical stress caused by water turbulence [17], [19] and grazing [15], [20].


This is the link to reference 16, but you have to buy it to view it:

http://www.sciencedirect.com/science/article/pii/S1568988305001149

 

[JonasRoman]

nice link
I understand that turf algues grow faster than macro, and that is at least intuitive easy to adept. I also realise that even if the photosyntetic activity per square mm is equal between micro and macro algue, the micro have the advantages to have same structure over all, but the macro have stem and o polymorph histology, which maybe takes som more energy to build up. But i think this is multifactorial, so i still seeking the answer if there is less dense with chloroplasts in the stem and/or other higher histological structures that is unique for macroalgue. If it is, this is at least a contributing factor to why an algae scrubber is more efficient than a macrorefugium? It is as i said this situation in the fauna above the water (as i said concerning the garden and some unwanted plants), so it is interesting if someone know if there is difference in chloroplast density between macro and microalgue so to speak. Sorry for my bad English, hope you understand my point. Thanks again for rapid and as always very dense answer
Jonas