Will an UV Sterilizer reduce phosphate uptake by SPS corals?

[Dr. Jim]

I've read in a few different places that SPS corals cannot absorb phosphates directly from the water, but rather, indirectly, by consuming phytobacteria (which have ingested/consumed the phosphate). I believe Red Sea Aquarium Systems is one source that has claimed this. If this is true, then wouldn't it be detrimental to run a UV sterilizer being that some phytobacteria would be killed thereby reducing the amount of the phytobacteria food source (containing phosphates) reaching the corals?

It would be nice to know:
1) Does anyone know any references in the literature that supports this claim that phytobacteria is instrumental in phosphate transport to corals)?
2) Has anyone run UV sterilizers and seen detrimental effects on their corals (such as turning pale) or possibly seen phosphates rise (as a suspected result of less phosphate being assimilated)?

 

[AlexG]

I have not read any literature on your first point but I will say that if a coral consumes a food item it will utilize some of the nutrients carried within the food source. I am sure there are a few folks on here that can better reply to the first point.

From my experience running a UV sterilizer on my system I have not seen any ill effects on the corals over time. Its important to remember that while a UV sterilizer does kill bacteria and pathogens when properly configured it cannot get them all. Water flow through a system will also impact how effective UV is as many people myself included run their UV sterilizer off of a manifold or a separate return pump. My UV sterilizer only turns over the tank water volume every 4 hours so it will never get it all. Depending on the source of living foods that corals get that are reproducing on their own in a system the UV sterilizer might not impact that life at all before it gets to corals. In my system the UV sterilizer is placed right after the skimmer and the main drain into the sump and water travels to the refugium or secondary sump before going back to the main return pump. The other factor to consider is that most corals are not picky when it comes to food and while the UV sterilizer might kill an organism it does not mean that a coral would still not eat that dead organism if the opportunity presents itself. There are many opinions on the usefulness of UV sterilizers on reef tanks but based on my experiences I will continue to use one on my current system and future systems.

 

[Dr. Jim]

I believe I should have used the term "bacterioplankton" in my original post, not phytobacteria. Sorry.

Bacterioplankton means: bacterial component of the plankton that drifts in the water column.

I don't mean to get into a discussion of the pros and cons of using UV sterilizers, but only to discuss an UV sterilizer's role in possibly inhibiting the uptake of phosphates into SPS corals by reducing the bacterioplankton population, along with any associated detrimental effects that may result. (Of course the bacterioplankton population would never be completely eliminated, but if it is true that the corals are dependent on bacterioplankton for phosphate transport then any degree of reduction could be deemed undesirable).

 

[Lasse]

I do believe that the Zoox can utilize PO4 from the water and therefore the combination of coral animals and algae can use both pathways for P into the organism. However if you run a ULS system - you must relay on bacterioplankton in order to get P to both the zoox and the coral animal. In my system - I do not run UVC and not either collect skimate for the moment. I do not run an ULS system but with providing both PO4 in the water column and P through prey of bacterioplankton I cover both pathways for P into the combined zoox/coral animal system.

I think it depends a little what you want to achieve with using an UVC steriliser - if you goal is to manage your anti - disease strategy with killing organisms that can be harmful - your corals may mostly just balance on one leg according to gain P - but in my case there the disease management is more close to herd immunity and to strengthen my organisms immunity - I do not need an UVC in the main aquarium. I get a more stable system in many ways. I do run an oxidator (another bacterioplankton killer) but its main task is to get my water more free from yellowing substance - therefore a very low dosage.

Sincerely Lasse

 

[Dr. Jim]

I do believe that the Zoox can utilize PO4 from the water and therefore the combination of coral animals and algae can use both pathways for P into the organism. However if you run a ULS system - you must relay on bacterioplankton in order to get P to both the zoox and the coral animal. In my system - I do not run UVC and not either collect skimate for the moment. I do not run an ULS system but with providing both PO4 in the water column and P through prey of bacterioplankton I cover both pathways for P into the combined zoox/coral animal system.

I think it depends a little what you want to achieve with using an UVC steriliser - if you goal is to manage your anti - disease strategy with killing organisms that can be harmful - your corals may mostly just balance on one leg according to gain P - but in my case there the disease management is more close to herd immunity and to strengthen my organisms immunity - I do not need an UVC in the main aquarium. I get a more stable system in many ways. I do run an oxidator (another bacterioplankton killer) but its main task is to get my water more free from yellowing substance - therefore a very low dosage.

Sincerely Lasse

Lasse, Thank you for your reply.
I have never used UV sterilization in my 50+ yrs of reef-keeping except on Q-tanks. I recently put one on a 4 month old 170L/(40 gal) tank because I had some fish break out with cutaneous bacterial infections. I removed all the fish for 3 weeks for treatment and just thought I would run the sterilizer for awhile on the DT. Although I'm sure most would not recommend this, I've added quite a few SPS coral frags to this "young" tank, fully aware that I have to be especially vigilant with every detail because of it's "age." Some of my frags have turned pale and I was concerned that the slightest disturbance, such as reducing the bacterioplankton, might push them in the wrong direction. I just now turned off the UV, not wanting to take the chance that bacterioplankton reduction could be a possibility.
(The pale corals I believe are due to my nitrates and phosphates dropping too low, which I am correcting).

 

[Timfish]

As phototrophs or mixotrophs corals can switch back and forth between autotrophic feeding, using inorganic nitrogen and phosphorus (PO4), or heterotrophic feeding, using organic sources like zooplankton or bacterioplankton. Tricky part is each species has preferrences, what one species likes maybe deleterious to another. From my understanding of the biology of hermatypic corals or corals with zooxanthellae simbionts I don't see how a species (Order, Family or Genus) could only be classed as a heterotroph, unable to make used of inorganic nitrogen and phosphate.