[kimoyo]

I was involved in a discussion about a week ago I found very interesting. A guy on RC posted a research paper that looked at the best type of flow for corals with actually video evidence. Probably not a big surprise to people but they found oscillating waves with shorter periods improved mass transfer. The paper explains that mass transfer rate is "the rate at which coral transfer nutrients, remove wastes, and exchange gas".

Quote: <a href=showthread.php?s=&postid=10854003#post1085400 3 target=_blank>Originally posted</a> by MCsaxmaster The abstract: Rates of mass transfer in coral reefs are governed both by the physical flow environment and the morphology of the coral. Laboratory experiments were conducted to estimate mass transfer in unidirectional and oscillatory flows by measuring the rate of dissolution of gypsum cylinders (clods) placed within the branching structure of three morphologically distinct coral species. Unidirectional flows were varied between 2.9 and 14.1 cm s21 and, as expected, mass transfer rates increased with increasing flow and a more open branch spacing. Depending on morphology and flow, mass transfer rates within the interior of the branching structure were 50 to 75% of that measured outside the coral in free-stream conditions. Oscillatory conditions showed relative mass transfer rates 1.6 to 2.9 times greater than equivalent unidirectional currents. This ratio increased with increasing wave frequency, likely due to the corresponding decrease in the diffusive boundary layer thickness. The ratio also increased with a greater compactness in branch spacing, with mass transfer rates within the coral structure up to 130% of free-stream conditions. We used planar laser-induced fluorescence imaging to study the instantaneous structure of mass advection through the coral. Oscillatory flow acts as a dominant forcing mechanism to generate water motion within the coral structure at levels not attainable with comparable unidirectional currents. From the discussion: "For all the corals, the increase in relative mass transfer ranges between a factor of 1.6 for a T=5s wave period to 2.9 for a T=1s wave period. The increase for the free stream control under waves versus unidirectional currents was 1.3 to 1.4, though no statistical relation to wave period was found. This 30% to 40% increase in mass transfer under waves is the same as that found in field observations by Falter et al. (2005)." So, the difference in mass transfer for the study corals between unidirectional and oscillatory flow was a factor of 1.6 - 2.9 depending on wave periodicity. For free gypsum blocks the factor was 1.3 - 1.4 without an obvious pattern due to wave periodicity. Best, Chris

Nice video of research
http://www.aslo.org/lo/toc/vol_51/issue_2/1134a1.html

Paper in pdf
http://www.stanford.edu/~vittorio/Reidenbachetal2006.pdf

[2Sunny]

That is really cool, but reading that study gave me a headache Seems like producing waves with a period of of 1 to 5 secs is tough in our reef setups, and I was about to be disheartened until I read:

Quote: This indicates that our measured increases can be due either to changes in flow or turbulence, but in all likelihood, is due to some com- bined effect of both.

So my short take is - wave action great, but turbulent flow is o.k. too.

There it is I have proven my predisposition to be true. Now don't try to convince me otherwise or I may have to get cross

Great find and thanks for sharing!!


Joe

[kimoyo]

Aquasurf!!! Just came out last month. Can produce wave from any controllable tunze. Neptune thinks it can produce waves in as small a tank as 1'. They can pulse tunzes at 0.1 sec which is ridiculous.

[jhale]

aquasurf http://www.marinedepot.com/ps_ViewIt...ct~NS8111.html

looks cool

[nyfireman3097]

nice read

[2Sunny]

So, today I took a closer look at my Tunze controller and realized that I had the ability to reduce the periodicity down to 1 sec cycles for the wave action. Its pulse waves, not back and forth, but I thought what the heck I'll give it a try. Anyways, there is some further background information that is interesting as well. Last year I gave a frag of my Oregon Tort to a local friend and fellow reefer. In his tank the polyps were fully extended. In my tank the polyps were never visible. The coral always grew well, but I simply never observed any polyp extension what so ever. So now today I adjust my Tunzes to a 1 sec periodicity instead of a 15 sec periodicity, and within seconds I notice polyps extending on my Tort colony. I turn it back t 15 secs and polyps disappear. I turn it back to 1 sec and polyps reappear. Now that is something! Too bad I'm not in college; sounds like a great paper in the making.


Joe

[Phyl]

Interesting experiment, Joe. I may have to try that. I'm pretty sure I'm turned up closer to 15s also.

Jake Adams will by speaking on flow dynamics on the 27th at the frag swap. Should be an interesting presentation.

[kimoyo]

Hey Phyl,

I'm not sure if I will be at the NJ frag swap. If you wouldn't mind please ask Jake about this paper and with so many wave making devices about his thoughts on a gyre vs. wave maker in a home aquarium.

Thanks.

[GreshamH]

I'll ask him for yah I'll point him to this thread as well

[NYreefNoob]

ive noticed with using hydroflors attached to my powerheads, my sps seem to do much better, it's a alternating flow around the tank, had tried my ph's in all different angle positions ect, but have gotten best results from using these

	SPS Small Polyped Scleractinians - Sometimes known as Small Polyped Stony corals. These are hard corals that have extremely small polyps. They are typically on the difficult side and require Metal Halide lighting or dense Power Compact or T5 arrays. These corals are prized for their rareness and ability to be easily fragged into multiple colonies.