Do high N:P ratios cause corals to bleach? (& get gout?)

[ichthyoid]

In the article below, researchers have found that high nitrogen to phosphorous ratios (N : P) can limit availability of carbohydrates produced by zooxanthellae to coral metabolism. There is also evidence of formation of uric acid crystals in images from scanning electron microscopes. Who knew?

Phosphate deficiency promotes coral bleaching and is reflected by the ultrastructure of symbiotic dinoflagellates

Enrichment of reef environments with dissolved inorganic nutrients is considered a major threat to the survival of corals living in symbiosis with dinoflagellates (Symbiodinium sp.). We argue, however, that the direct negative effects on the symbiosis ...

www.ncbi.nlm.nih.gov

 

[ichthyoid]

Of particular interest -

‘In coral reef waters, N : P ratios were found in an approximate range from 4.3:1 to 7.2:1 (which is an avg of 5.75 : 1) which is lower than the Redfield ratio of 16:1, considered optimal to sustain phytoplankton growth’

 

[Adam]

Randy Holmes-Farley has not been an advocate of keeping our tank water within the Redfield ratio. His assertion is this is the ratio found in the plankton biomass but not the actual water.

What are your thoughts on Redfield?

 

[sharis100]

A lot of folks run beautiful tanks with healthy colorful coral and do not maintain or chase a Redfield N to P ratio. I think that it is a helpful ideal not a goal and anything close with a healthy tank is fine.

 

[ActiveAngel]

Haha, i delivered a presentation on this exact research article last year. People were calling me and talking about it for a couple weeks, and began using me as a reference/example. It definitely left a positive impact on everyone, which always makes me feel happy.

Super interesting article! And easy to read. Highly recommended.

(For anyone who doesnt usually read these things, theres a lot of not-so-great articles out there too. Lol)

 

[ichthyoid]

The premise here, backed by research, is that natural seawater N : P ratio for coral reefs is ~6 : 1

The Redfield ratio for N : P, within the bodies of phytoplankton, is 16 : 1. Which means the phytoplankton have retained more nitrogen within their tissues, than exists in the water around them.

The study concludes -

‘Our results suggest that symbiotic corals can tolerate an undersupply with nitrogen much better than an undersupply with phosphorus. These findings likely reflect an adaptation of the algal symbionts to the nutrient environment of coral reefs where processes are mostly nitrogen limited’

I often see reefers state that high nitrate doesn’t matter, and high phosphate does. That is not in agreement with observed coral behavior, per this study.

Instead, it has been observed that corals exposed to high nitrate + low phosphate become much more sensitive to high temperatures and light conditions. This is also referenced.

How many times have we seen someone say, ‘everything was fine’?… ‘Nitrate was 30 and phosphate was less than 0.1, then all of a sudden my corals started bleaching for no reason!’

It’s obvious that Redfield did fine work on phytoplankton, but that work bears limited meaning for other organisms. Other than they have their own respective ratios & the environments they live in as well.

I think it is important to remember that these ratios are for nitrogen and phosphorous, not nitrate and phosphate like our test kits can (loosely) measure. To understand the difference requires knowledge of mole theory from physics/chemistry, which I’m not going into here. Many people I was in school with didn’t understand it, just know there is a difference. Maybe I should do the math and state the molar equivalents for nitrate & phosphate later?

Anyway, my take away here is that: limiting inorganic nitrogen in a reef tank, is probably much more important than most of us believe. At the very least, keeping nitrogen and phosphorous in balance is very important!

There are other possible reasons for mass bleaching on coral reefs, besides elevated water temperatures, such as elevated nitrogen levels from human activity. Like sewage leaching, fertilizer runoff, dumping, stack gases, etc.

-Too little nitrogen, coral growth slows.
-Too little phosphorous, corals fade or bleach & show increased sensitivity to light/heat
-Too much phosphorous is not much of a problem for the coral itself.
-Too much nitrogen causes corals to display symptoms similar to too little phosphorous (above)

 

[sharis100]

The premise here, backed by research, is that natural seawater N : P ratio for coral reefs is ~6 : 1

The Redfield ratio for N : P, within the bodies of phytoplankton, is 16 : 1. Which means the phytoplankton have retained more nitrogen within their tissues, than exists in the water around them.

The study concludes -

‘Our results suggest that symbiotic corals can tolerate an undersupply with nitrogen much better than an undersupply with phosphorus. These findings likely reflect an adaptation of the algal symbionts to the nutrient environment of coral reefs where processes are mostly nitrogen limited’

I often see reefers state that high nitrate doesn’t matter, and high phosphate does. That is not in agreement with observed coral behavior, per this study.

It has been observed that corals exposed to high nitrate low phosphate become much more sensitive to high temperatures and light conditions. This is also referenced.

How many times have we seen someone say, ‘everything was fine’?… ‘Nitrate was 30 and phosphate was less than 0.1, then all of a sudden my corals started bleaching for no reason!’

It’s obvious that Redfield did fine work on phytoplankton, but that work bears limited meaning for other organisms. Other than they have their own respective ratios & the environments they live in as well.

I think it is important to remember that these ratios are for nitrogen and phosphorous, not nitrate and phosphate like our test kits can (loosely) measure. To understand the difference requires knowledge of mole theory from physics/chemistry, which I’m not going into here. Many people I was in school with didn’t understand it, just know there is a difference. Maybe I should do the math and state the molar equivalents for nitrate & phosphate later?

Anyway, my take away here is that: limiting inorganic nitrogen in a reef tank, is probably much more important than most of us believe. At the very least, keeping nitrogen and phosphorous in balance is very important!

There are other possible reasons for mass bleaching on coral reefs, besides elevated water temperatures, such as elevated nitrogen levels from human activity. Like sewage leaching, fertilizer runoff, dumping, stack gases, etc.

-Too little nitrogen, coral growth slows.
-Too little phosphorous, corals fade or bleach & show increased sensitivity to light/heat
-Too much phosphorous is not much of a problem for the coral itself.
-Too much nitrogen causes corals to display symptoms similar to too little phosphorous (above)

Having the molar equivalents or providing a ratio that routine test kits can produce data to calculate - like a reef calculator converter - would be more useful than the just quoting the Redfield ratio which can only loosely be translated without doing the balanced equation calculations that my brain does not want to remember from back in my chemistry TA days.