Reef Chemistry Question of the Day #185 Macroalgae and Nutrient Uptake

[Randy Holmes-Farley]

Reef Chemistry Question of the Day [HASHTAG]#185[/HASHTAG]

Many people grow macroalgae in reef tanks in an effort to reduce nutrients (especially nitrate and phosphate), and it can be a successful method. I use it, along with other methods.

The exact ratio of nitrogen to phosphorus in macroalgae reflects what it took up from the water. This ratio depends not only on the species involved, but, in some cases, on the concentrations of nutrients available to it since they can take up somewhat more N (nitrogen) or P (phosphorus) when more is available.

The species effect alone can alter the relative amounts of N and P by more than a factor of two, but the values are typically clustered reasonably close together because most of the biochemical molecules of life that contain N and P are similar in different species, such as proteins, DNA, RNA, phospholipids, etc.

In typical macroalgae grown in the ocean, which ratio below is closest to the average weight ratio of nitrogen to phosphorus atoms (N) found in the macroalgae?

A. 1:20
B. 1:1
C. 20:1
D. 200:1

Good luck!

































.

 

[Drauka99]

C

 

[beaslbob]

c

 

[nervousmonkey]

C

 

[innerspark]

Def C

 

[Salty1962]

Yep C

 

[wpeterson]

C. 20:1 (the Redfield Ratio)

 

[klp]

C

 

[fab]

The answer is "C", from Redfied, which is 16:1.

 

[Tdawg]

+1

 

[beaslbob]

something is telling me this was too easy.

 

[go_bucky]

I'm with beaslbob, this seems like a trick question. Wasn't the Redfield Ratio calculated using worldwide average of all marine plant life, which is primarily phytoplankton? The question is about macroalgae, and I seem to recall reading an article that some caulerpa algaes had N ratios of as high as 180:1. Unfortunately I can't find that reference. How about it Randy?

 

[aaron23]

agree with c

 

[go_bucky]

Found the reference: http://web.mit.edu/qhorn/Public/Reef Aquariums/Phosphorus articles/Larned Marine Bio 132 1998.pdf

Table 2 Nitrogen and phosphorus concentrations (% dry wt) and total nitrogenhosphorus (TN:TP) ratios in macroalgae tissues under field conditions. Values are means of four samples ‹1 SD
Species TN:TP
....
Caulerpa racemosa 148.7:1
Caulerpa sertularioides 198.9:1
....
There are many more. These are the ones I was referring to.

 

[beaslbob]

Is it a difference between weight and ions?

 

[go_bucky]

@beaslbob, probably it is. This very question has been on my mind for some time -- I'm just here to learn so I look forward hearing the explanation. The real meat of the issue for me is finding out what species of plant material is best for a large fuge (no skimmer, preferably no gfo) system. So if caulerpa has a high N to P ratio relative to the redfield ratio, it might not be the best macro to grow in order to keep phosphates in check. And I'd really like to determine if true sea grasses (such as turtle grass) would be a better option.

 

[beaslbob]

@beaslbob, probably it is. This very question has been on my mind for some time -- I'm just here to learn so I look forward hearing the explanation. The real meat of the issue for me is finding out what species of plant material is best for a large fuge (no skimmer, preferably no gfo) system. So if caulerpa has a high N to P ratio relative to the redfield ratio, it might not be the best macro to grow in order to keep phosphates in check. And I'd really like to determine if true sea grasses (such as turtle grass) would be a better option.

I have heard of sea grasses being used with success but they do require a deap substrate like 6" or more for turtle grass.
the caulerpas emit stuff which is detrimental to corals (caulerpins?) and everyone (but me) worry about them going sexual.
So most go with chaeto.

Still, with all that, a tank started with macro algaes to me is best or possibly with an algae turf scrubber as a close second.

It would seem the hard macros like halimeda would make an excellent in tank "plant" for reef displays. if for no other reason because, when halimeda thrives corals will probably also.

but then what do I know.

 

[go_bucky]

I agree with everything you've said. I've been establishing a 45 gal fuge for the past 6 months on a new tank. The oolitic sand is 7" deep, and I mixed in some mud as well. I have about 10 turtle grass plants started, but they take a long time to become established. I'm growing chaeto and a couple types of gracillaria for nutrient export while the turtle grass takes hold. The chaeto is growing well but its a problem as I have to keep it confined to one edge of the fuge tank to allow light for the turtle grass. I had caulerpa sertularioides growing for a while, but it went sexual -- I'm avoiding all caulerpa indefinitely. I've given some serious thought to an algae filter, but there again, I suspect that turf algae would assimilate more nitrates than phosphates (high N to P as compared to Redfield) and I want to avoid or minimize the use of gfo. As I said, I'm just here to learn.

 

[beaslbob]

If you get the ratios wrong, I have a strong suspicion something like cyano will step up which can get nitrogen from nitrogen gas vrs nitrates. By killing the lights (or limiting the lights) and limiting feedings I think cyano would die off and return whatever is "missing" to the macro or grasses. So eventually you will arrive at some equilibrium where the macros/grasses thrive and cyano is held at bay.

Just my suspicion tho and worth at most .02

 

[go_bucky]

If you get the ratios wrong, I have a strong suspicion something like cyano will step up which can get nitrogen from nitrogen gas vrs nitrates. By killing the lights (or limiting the lights) and limiting feedings I think cyano would die off and return whatever is "missing" to the macro or grasses. So eventually you will arrive at some equilibrium where the macros/grasses thrive and cyano is held at bay.

Just my suspicion tho and worth at most .02

Thanks for the comments and 2 cents is apparently worth quite a bit these days I battled cyano in the fuge for a couple of months but that's subsided for about a month now. I limited light to the display tank for the first four months to avoid a cyano or gha outbreak there (successfully), but started adding corals last month and cranked up the lights. I now have a beautiful field of gha on my rock -- certainly due to food settling in the pukani during the previous months. So I'm hoping that will clear in a few weeks with the fuge outcompeting it, along with help from my two 7 inch five fingered hand tangs.