The editorial article in December's issue brought back some memories from college ecology. A professor of mine studied oyster density and nutrient levels. Loosely paraphrasing his findings, he found that oysters leech nutrients into the water to promote algae growth and that tidal creeks with the oysters removed actually had lower nutrient concentrations than those with oysters. A similar phenomenon has also been found to exist on eelgrass beds in the tropics, where eelgrass actually contributes to nutrient levels. For this reason, I have never employed an algae refugium myself. Many people rely on algae refugiums and algae "scrubbers" to remove nutrients from the water. While algae scrubbers have certainly proved valuable in industrial settings, is it possible that they are counter-productive at the relatively low (as opposed to a sewage treatment plant) nutrient levels we find in our aquariums. We need an industrious and intelligent reefer to do some scientifically sound research to investigate this matter.
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Algae Refugiums
- Thread starter dvmsn
- Start date
I think the part of the equation you may be overlooking is that in an algae refugium algae is harvested regularly, exporting nutrients. In an eelgrass bed the old leaves will be reincorporated into the system.
As far as the oysters go- I don't know. Large amounts of any animal certainly will be releasing waste, but I would expect that generally in an ecosystem the end balance of nutrients would be 0.
I do know that in the Hudson River and Great lakes the invasion of zebra mussels has left the water much clearer; enough to substantially change habitats.
As far as the oysters go- I don't know. Large amounts of any animal certainly will be releasing waste, but I would expect that generally in an ecosystem the end balance of nutrients would be 0.
I do know that in the Hudson River and Great lakes the invasion of zebra mussels has left the water much clearer; enough to substantially change habitats.
I think that those are both excellent points. My argument it simply this. The notion that macro algae, even when regularly harvested from a refugium, removes nutrients is an assumption. Eel grass leeches phosphate into the water as a living plant. Living oysters do the same thing. The papers on oyster beds are written by Dr. Richard Dame of Coastal Carolina University. It doesn't make sense that a creek full of filter feeders would have elevated POC levels, but his studies indicate that they do. Ecosystems do not always work the way we think they do. For those of us who started out in the days of bare bottom tanks, the idea that deep sand bed/plenum system would be able to "absorb" the nutrients and waste in our tanks without becoming overloaded and causing and algae bloom seemed unlikely. However, for reasons we are just starting to understand, this is possible.
dvmsn":3cv3gxxo said:I think that those are both excellent points. My argument it simply this. The notion that macro algae, even when regularly harvested from a refugium, removes nutrients is an assumption.
Actually, I think somebody just did a comparison study on that... measuring the dry weight of algae that was harvested...
Randy-Holmes Farley in Advanced Aquarist :
http://www.advancedaquarist.com/issues/sept2002/chem.htm
- Mac
Again, even this article makes a large assumption. It assumes that nutrient uptake and assimilation works at a one to one ratio. That is since the plant produced X amount of mass, and there is x amount of phosphoreus in X mass, X amount of phosphoreus was "taken" from the water column. But his doesn't address the system as a whole. Lets assume the pathway works something like this. You also have live sand in your refugium. Typically the sand bed serves as a nutrient sink. You have planted Caulerpa sp. in your refugium. It sends out it typical runners into your bed. It pumps nutrients from the sediments that were already "locked" in place and incorporates them into its tissues. Has it reduced the amount of nutrients available in the water column. Probably, but is it necessarily on a one to one basis, no. After all, its the available nutrients that we are concerned about. Now lets go one step further, assume that the algae pumps nutrients from the sediment. Some are incorporated into tissues, the excess is released into the water column (as is common in many see grasses) See how this would actually increase the amount of nutrients available in the water column. These are all theories, and absolutely not proven, and should not be relied on. However, when you look at the anecdotal observation noted in the editorial of this months issue of AA, that hair algae blooms are often associated with algae refugiums, it seems possible.
Personally, I don't really need equations derived from empirical data to be convinced that algae/substrate/live rock refugiums work. My water quality tells me it does. In over 1 year's time, I've had no detectable nitrogen cycle or phosphate on a newly set-up 90 and 120 plumbed into an 80 gallon sump/refugium/plenum.
I'd like to recap some of the theoretical advantages of a refugium (some more solidly based in fact than others)
1. refugiums lighted 24/7 or 12 reverse cycle moderate/lesson pH drops after main tank lights out.
2. Fuges provide a greater water volume and greater stability over time
3. Fuges act as a settling point for detritus.
4. Fuges are a great place to monitor water level, and add supplements
5. Fuges are a constant source of zoo/phytoplankton.
6. Fuges allow for nutrient export by means of algae harvest
7. Larger fuges can be used as a "hospital ship" if something goes wrong (a leak) in the display
8. Fuges eliminate many diseases such as lateral line disease, and it seems anecdotally, to inhibit Ich.
These are by no means scientific laws. But experience over ten years of keeping marine life, and 5 years of refugium filtrating leads me to lean towards believing that most of it is valid.
I'd like to recap some of the theoretical advantages of a refugium (some more solidly based in fact than others)
1. refugiums lighted 24/7 or 12 reverse cycle moderate/lesson pH drops after main tank lights out.
2. Fuges provide a greater water volume and greater stability over time
3. Fuges act as a settling point for detritus.
4. Fuges are a great place to monitor water level, and add supplements
5. Fuges are a constant source of zoo/phytoplankton.
6. Fuges allow for nutrient export by means of algae harvest
7. Larger fuges can be used as a "hospital ship" if something goes wrong (a leak) in the display
8. Fuges eliminate many diseases such as lateral line disease, and it seems anecdotally, to inhibit Ich.
These are by no means scientific laws. But experience over ten years of keeping marine life, and 5 years of refugium filtrating leads me to lean towards believing that most of it is valid.
I find those oyster results disturbing. So he actually removed the oyesters from a tidal creek, and measured the nutrients before and after?
Assuming that the oysters are strictly filter feeders, it seems odd that the nutrients would be lower with them missing. Did he include or exclude plankton as part of the "nutrients"? Also, removing an oyster bed would have considerable impact on the local habitat- tidal movement could easily sweep debris free from the substrate where it was previously held by the oysters. This in itself could have a large impact.
All organisms remove more nutrients from their environment than they put back due to the energy requirements of living.
Assuming that the oysters are strictly filter feeders, it seems odd that the nutrients would be lower with them missing. Did he include or exclude plankton as part of the "nutrients"? Also, removing an oyster bed would have considerable impact on the local habitat- tidal movement could easily sweep debris free from the substrate where it was previously held by the oysters. This in itself could have a large impact.
All organisms remove more nutrients from their environment than they put back due to the energy requirements of living.
I'm also confused about why sea grasses release nutrients from their leaves. This would appear to be a wasteful and counterproductive activity. Are you sure the nutrients aren't from decaying leaves?
Also, its not an assumption that algae removes nutrients from the water, its a fact. They can't grow from nothing.
I'm not a scientist, so just guessing on all this...
Also, its not an assumption that algae removes nutrients from the water, its a fact. They can't grow from nothing.
I'm not a scientist, so just guessing on all this...
The oysters were removed from certain creeks. I tried to find the papers online, but could not. I wish I could give you some more specific info about his methods. I'm not arguing that a refugium is a bad thing, or that overall refugiums dominated by macro algae are a bad addition to the system as a whole. I'm just saying that it is not proven as an effective system for nutrient export.
You have planted Caulerpa sp. in your refugium. It sends out it typical runners into your bed. It pumps nutrients from the sediments that were already "locked" in place and incorporates them into its tissues.
-The caulerpa species in my refugium do not send their holdfasts into the sediment. Even if they did, these are not used for nutrient up take.
Steve
I hear what you're saying dvsmn, there hasn't been that firm 'proof', that the theory works. I think it's just one of those things where if it walks like a duck and quacks like a duck... There's quite a bit of 'anecdotal observations', that it does work, just no scientific work done to verify the supposed pathway.
- Mac
- Mac
i'm not sure that it work or not but it seems to make some of my softy go unhealthy when the algae/seagrasses start to grow large in my refugium. i would remove it soon. I think a skimmer works better wihtout side effect. I have lost my interest in monoculture filter system.
dvmsn":qji5hq93 said:The editorial article in December's issue brought back some memories from college ecology. A professor of mine studied oyster density and nutrient levels. Loosely paraphrasing his findings, he found that oysters leech nutrients into the water to promote algae growth and that tidal creeks with the oysters removed actually had lower nutrient concentrations than those with oysters. A similar phenomenon has also been found to exist on eelgrass beds in the tropics, where eelgrass actually contributes to nutrient levels.
As a professional scientist I would have been skeptical (and told the prof so) if I would have been there. It is not possible to get more out of a system than you put into it without great depletion of resources from the system. Soooo, how do the oysters do so without starving themselves? No doubt with the oysters' excretion of wastes, there would be nutrients released. However, as long as the oyster is growing the net should be removal of nutrients from the water column since oyster tend not to be photosynthetic and feed off what is floating by. The oyster beds I used to see by Reedsport, OR used tidal imputs of seawater for oyster culture. Admitedly that is a different ecosystem than freshwater, but the concept should still hold. Eel grass/turtle grass beds are nutrient (detrital sinks) and hence their higher levels. Again, this is from imports from the outside (carbon from the atmosphere, light energy, elements from the water column and detritis from offshore). If your prof can point us to the references of those studies and reviews thereof, I'm sure they would be of interest to us here. Anyway, my $0.02 and some food for thought. And yes, I run with a refugium-mostly because I like the look of one on display.
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