The article below is the only places I’ve seen the case for urea. I actually plant to give it a try along with ammonia as an experiment.
https://www.sciencedirect.com/science/article/abs/pii/S0166445X18302200
Maybe correct, but zooxanthellae growth should be limited. Evidence and theory say that under unlimited growth zooxanthelle use all the chemical energy they produce for their own growth and corals may be starved or at least much worse nourished than with growth limited zooxanthelae.
This might have been the article @Salem-Novel Aquatics was referring to that he misplaced when he wrote down the rabbit hole on reef builders.
It is cited under [9] in the rabbit hole article.
This is nearly exactly what Borneman in his book Corals published in 2001 writes, “when the zooxanthellae have an enriched nitrogen environment, they do not translocate as much to the animal and instead use it for their own growth. Nitrogen-enriched waters, therefore has an immediate effect of stimulating a larger zooxanthellae population, which in turn creates a higher demand for carbon dioxide that may or may not be met. Nitrogen enrichment can also directly block photosynthesis by interfering with photo absorption…. there are also as many study showing that nitrogen enrichment significantly reduces, calcification, photosynthesis and respiration rates and even reduces skeletal density.” Borneman cites numerous studies to this effect from Kinsey and Davies 1979 to Marubini and Davies 1996.
Thank you very much! That was very helpful.I want to come back to the iron question. It doesn't exactly fit here but I think Claude's "bolus" effect might also be related to iron precipitation. Increased pH and alkalinity could precipitate iron that has dissolved under lower pH and lower oxygen concentrations during the night and restore the positive (especially for coral coloration) low iron concentrations.
Maybe correct, but zooxanthellae growth should be limited. Evidence and theory say that under unlimited growth zooxanthelle use all the chemical energy they produce for their own growth and corals may be starved or at least much worse nourished than with growth limited zooxanthelae.
The first guess for a good growth limiting nutrient would be phosphate in my eyes because phosphate plays a major role in propagation and cell division. This was my approach around 30 years ago but at some point, maybe 24 years ago, I had to accept I was on the wrong track. Phosphate limitation did not improve coral growth, health and coloration but the opposite. Now my favourite is a nitrogen-iron-colimitation.
Edit: ... well, maybe iron limitation allone is also good ... as concenssion to all high-nitrate-advocates.
Do you agree that zooxanthellae growth should be limited and too much can actually be worse for the coral? I read about them outcompeting corals for (carbon?) This always kind of confused me because I’d assumed more zooxanthellae = more photosynthesis that the coral can gain energy from. How can they outcompete energy from corals?
One common hypothesis is that when the growth of symbionts is no longer limited by certain nutrients, such as nitrogen, much of their photosynthate will be used for proliferation rather than being translocated to the host. This scenario is somewhat analogous to carbon dosing in a tank with depleted nutrients, where heterotrophic bacteria are unable to proliferate due to the lack of materials needed to build biomass. As a result, the added organic carbon is primarily metabolized through respiration rather than being assimilated into new cells.
The concept is quite simple: Zooxanthellae, just as other microalgae, need all nutrients for growth and division. If one nutrient is lacking they can't unfold their full growth potential. However, photosynthesis cannot be switched off when algae are exposed to light. Light energy is collected and without discharge would destroy the photosynthetic apparatus. So the light energy is used to build organic carbon compounds from CO2 and water like "normal". Since the alga cannot use the glucose and other organic carbon compounds, which are formed, for growth it just excretes them into the water, or in the case of zooxanthellae into the coral. It is a natural process that foundet the symbiosis between coral and zooxanthellae.
Can't corals limit zooxanthellae growth themselves? We know that corals can "cleaning house" when the temperature gets too high, what we call "coral bleaching".
Can the Zooxanthellae inside the coral also excrete organic carbon to the water column?
