Two Random Questions

[frogdog]

Two questions, folks:

Is there any evidence that green macroalgae exports more or less nitrogen compounds and phosphate than red macroalgae?

If one of the reasons people have sumps and water coursing through them is for oxygen exchange, then how much oxygen can be exchanged in a closed cabinet under the DT?

Thanks!

[Randy Holmes-Farley]

When you say exports more, presumably part of that is how fast they grow in a reef tank, and not just the relative amounts of N and P as a function of the dry weight.

The relative growth is hard to come by, but IME, green algae generally grow better in reefs than other types.

I expect that growth rate wins the day and that is why people pick green algae for refugia. Red algae that I have tried has always been outcompeted by the green.

If one of the reasons people have sumps and water coursing through them is for oxygen exchange, then how much oxygen can be exchanged in a closed cabinet under the DT?

FWIW, skimmers are the big aerators, not so much sumps, especially if covered. Yes, you want fresh air for aeration. Even indoor air in a home can have a lot more CO2 than outdoor air, driving down the pH. :)

[disc1]

1. I'm not aware of anything that says one uses more nitrogen than the other.

2. Gas exchange is going to happen as long as the stand isn't airtight. Most of it is happening via the skimmer if you have one. I think there are a lot of other reasons to have a sump though besides gas exchange.

[Randy Holmes-Farley]

This article gives N and P values (Table 2) for various algae species. You'l have to search to see which, if any, are red.

https://web.archive.org/web/20110409085504/http://www.botany.hawaii.edu/bot482/kaneohe%20bay%20algae%20n-p%20larned%20mar%20biol.pdf

[frogdog]

This article gives N and P values (Table 2) for various algae species. You'l have to search to see which, if any, are red.

https://web.archive.org/web/20110409085504/http://www.botany.hawaii.edu/bot482/kaneohe%20bay%20algae%20n-p%20larned%20mar%20biol.pdf

Thanks Dr. H-F. I actually looked at that article before. Table 2 shows different concentrations found in the tissue, but I'm not sure how you interpret that. Something with a high concentration of phosphorous may have been slowly growing for 20 years. Another with a lower concentration may have acquired that concentration in 6 months, no? I didn't understand how to interpret Figure 2. Some are having negative growth rates? And the description says it's macros that have been in enriched environments and the controls. Which are the controls?

You wanna give me the quick and dirty in little words? :D

[Randy Holmes-Farley]

Yes, the article says nothing about growth rate. It does show that a pound of one macroalgae does not equal a pound of another.

A negative growth rate means it lost some weight. Controls (C) had normal seawater, N had extra nitrogen, P had extra phosphate, N+P had both.

[frogdog]

Thank you Dr. H-F. :)

[billsreef]

Based on growth rates with both added N+P in that article, the fastest growing algaes in order are Ulva (a green), Gracilaria (red) and Sargassum (brown) are closely tied, and Caulerpa racemosa, then C. seretulides and Codium are pretty closely tied. The rest are fairly slow. For overall nutrient removal, the faster growers are generally going to the best for overall nutrient removal. The article does note that tissue content of N + P might be more reflective of the species need for that nutrient vs. absolute uptake rates.

Not from the mentioned article, but of interest for nutrient removal, Gracilaria is know for having a high capacity for uptaking and storing N during the night, for later use during daylight.

[tmz]

Kappaphycus alvarezii is also a rhodophyta,,red algae.
The TN: TP ratio for the Gracilaria as well as the Kappaphycus is about 30:1, a much lower proportion of N than the others. Anecdotally , I know in my tanks , reds do fine with low PO4 and NO3 and many of the greens don't .

[frogdog]

Thanks for explaining. I never read about anyone growing red macroalgae, but it sounds like there's no reason not to try it.

[billsreef]

The reds generally do well with somewhat lower lighting than the greens.

[Randy Holmes-Farley]

I never read about anyone growing red macroalgae, but it sounds like there's no reason not to try it.

There's a lot more folks who focus on macroalgae in the subforum linked below, but in my tank I never got Gracilaria to grow.

http://www.reefcentral.com/forums/forumdisplay.php?f=176

[frogdog]

Thanks Dr. H-F. Yeah, I have been reading that forum. I didn't see anything about the comparative take-up of N vs. P which is why I asked it here.