thoughts on clams...

[printerdown01]

*Figured I might as well take advantage on the Advanced Forum, and bring up some more "controversial" reefing issues... Which would confuse, rather than help new people...

 

Ok, this is one topic (referring to clams, remember this is a post about clams) that my ideas certainly seem to differ from everyone else here... I would like to think that these differences are caused by my wealth of experience (LOL), but I highly doubt it.... Ok, first thing first, where did people get info that baby clams need phyto dosages in order to survive (my guess is a company that makes phyto). From my understanding, clams are born without symbiotic algae in their mantles (it would be a neat trick if they came with it -haha). During their early stages of life they obtain their symbiotic algae by filtering water. I guess my problem with the idea that "young" clams need phyto is that they cannot utilize the types of algae that we are adding to the tank. Not only this, how young is young, by the time most clams reach 1 cm (negating predatation) they seem to level off in mortality rates (which would suggest to me that they are beginning to become much more efficient at producing their own food)...? Perhaps I am making rash assumptions.... Not to mention that when they reach the size of about 3mm you can already see the algae in their mantles!!! Also there are a lot of clam breeders that do not dose with phyto! I have a book on breeding clams that highly suggests using yeast to feed clams (both young and adult) -it also claims that blood works quite well, but wisely discourages against it since you can easily infect yourself with disease. By they time that we purchase 1-2" clams they are no longer really babies, but full grown clams... so I wouldn't even consider them young at this point.

 

Second thing, why such high lighting recommendations for clams, recently?? Lighting recommendations seem to flux on this board by the seasons... Last year around this time there were some people recommending 9W per gallon... then it went down to 4.5W... and now, a year later than when I originally joined, we are back to 9W. Negating the fact that I think W/gallon is an inaccurate way to measure lighting in the first place, why do you guys (the more experienced crowd) think that there is such a wide flux in peoples recommendations...? Perhaps it is just another aquarium fad?

**note, I realize that the people reading this, are probably not the ones that are guilty of constantly changing their mind about what level of lighting is required! I am just interested in hearing your thoughts. Also I figured that I can be a bit more cynical in the advanced forums, and give more straight forward opinions (rather than trying to explain the there is not just one right way to do things -since you guys already know this- which is often my point on the other forums).

[Lunchbucket]

well, i have no experience and haven't read that much about clams....though i plan to in the near future and then get one sometime soon.

 

as for the lighting issue i believe that people used high lighting (9wpg+, and yes wpg is a terrible indicator of lighting IMO) due to the fact that reef sun is VERY VERY intense. then this is my belief: peopl tried to find cheaper/easier/less light intese ways to attain the good coloration and rapid growth found in intensly lit reefs. they found that this does not work or doesn't work as well and the trends have come back to the higher lighting. this is all my theory though

 

i have had low light 2x36pc's w/ sps, 70w HQI, 150w HQI and now will have a 400w HQI and i do not believe that you can saturate a coral enough. i have never had a negative response to more light from a coral unless it was acclimated poorly.

 

just my insight, little experience, and MO

Lunchbucket

[barry631]

I am certainly no light expert but when keeping clams I think Daniel Knop refers to intense lighting rather that watt. Have heard for years that you can not keep clams under nothing but MH. This past year I have heard from many people that they are keeping clams under PC with great success. No doubt that MH will incease the symbiotic algae in their mantles but also there is a misconception that clams live solely on symbiotic algae. Daniel also goes on to say that " The presence of a fully developed intestinal tract with digestive glands, bowels, and anal papilla speaks for the contrary."

 

Printerdown01 is correct regarding the feeding of clams with yeast and blood and has proven to be good but hard to manage the correct dosage. If you feed your fish well in your tank, clams will also filter the waste from the fish as well.

 

Can only go by what I have tried. I set up 2 small tank and placed 15 small clam (1") in each tank with the same lighting and one I fed DT's and the other I fed no DT's and after 93 days, the one that I did not feed Dt's I lost 7. The other tank I lost none. A few small fish in each tank and feed the same fish food daily. So go figure

 

JMO

 

Barry

[Lunchbucket]

thank you for some insight. i too believe that they use both but from what i can reason it makes me believe that they use what they can get to a point. one system picks up the slack for the other. so if there is less light they use more from the water and vis versa....kind of a built in check and balance to help them through "less than optimal" conditions.

 

i am sure pc's can be done as i am sure NO's or VHO's could be but i wonder how or if we stress the animal to go into "survival" mode more than we should?

 

Lunchbucket

[barry631]

No doubt that you will have local bleaching due to the lost of symbiotic algae when they do not get enough lighting. Where as central bleaching is where all pigments are loss.

 

Barry

[printerdown01]

It is my understanding that the NEED both (light and filter-feeding) in order to survive. A T. clam could never sustain itself on light alone, nor could it sustain be kept solely with filter feeding (I think the latter is painfully obvious).

 

Thank you for sharing your own DT's data!! I was very skeptical of this info, as the only place I had read this information was on advertisements for 3 types of phyto (and boards, the persons shared their info failed to give references). Your observation give this claim credibility.

 

Another question... lighting is not my strong point... I don't understand HOW the actual light given off MH can be different from the light given off by a PC.

i am sure pc's can be done as i am sure NO's or VHO's could be but i wonder how or if we stress the animal to go into "survival" mode more than we should?

If you have the same number of lumens (and thus the same amount of candela) and the emittion is within the same spectrum, how can they possibly differ? ...or are you just saying that you would have to pack a lot of PC just to equal a MH? In terms of lighting frequency, amplitude, and quantity of photons –which I believe is accounted for in lumens- are the only variables (am I mistaken here...?). Thus, if you had the same color of light, and the same candela out put does the light source mater?? I am sure that there is an obvious answer that I am over-looking for some reason, as I stated before lighting is not my area of expertise...

[Lunchbucket]

just from what i have heard the point source of MH is much better. very centralized "beam" which is way more intense than a PC. i would venture to say it would be harder to look directly into 150w MH than 150w worth of PC or VHO. just more directed in one point like the sun. then again i am not a lighting technical person.

 

Lunchbucket

[barry631]

Daniel goes on to explain that local bleaching is different from central bleaching.

 

Local Bleaching: Daniel Knop

 

The area is characterised  by a complete loss of symbiotic algae but the protective pigments is retained and therefore the spots are not colourless but lose only the brownish tinge, In this respect it is different from central bleaching where all pigments are lost.

 

Hope this this clear up some question.

[tinyreef]

i agree with lunchbucket's idea on the intensity and concentration. a certain pc may emit the same amount of photons as a mh but not over the same area and not at the same energy level. the higher mE's emitted from the mh's allow further penetration into the water or body mass of the clams to reach all the symbiont algae.

 

the pc's are a diffused light versus the beam/concentrated light of the mh. a good analogy is if you keep concentrating the light until all the photons are aligned (coherent) it becomes a laser. zap-zap! i'm feeding the clams!

[Goofnut]

Hopefully this site will help refresh some of us on the concepts being discussed here:

 

http://www.westsidesystems.com/rays.html

 

Oh, and the next thing you will be lighting your tanks with (and soon to enter the great lighting debate):

 

http://www.spectrum.ieee.org/WEBONLY/publi...sep02/lite.html

 

We already do it for moonlight simulation, but I bet you didn't think you'd be replacing your aquarium lights so soon....

[MKramer]

To further expound on the beam tightness line of thought....

 

PCs or other tubes can of course be made to generate the same intensity of light as a MH at any one locaiton. It's less efficient (more light wasted, not necessarily less energy-efficient, MH being the electron-hogs that they are), but it's certainly doable. However, there is one quality you'll have a harder time duplicating: directionality.

 

The theory goes that some animals require light to be coming from a certain direction in order to use it. MH can easily do this in a parabolic fixture. The light is nearly columnated, and a good replica of natural sunlight's directionality. However, light from flourescents is by nature difuse. Only a small portion of it actually strikes the animals directly. Most the rest of it is coming at weird angles off the glass, hood, and reflectors. If such animals existed, this light would be much less useful to them. It would be like spending their entire lives in a cloudy environment, instead of the sunny tropical environment.

 

No,w I have no idea how true this biological quirk is for many of the species people claim as MH-only, but it's something to think about.

[Goofnut]

Interesting thought.. I don't have a free moment to investigate that further myself, but many corals, plants, etc. do position themselves to accept incoming light at optimal angles. I haven't specifically read anything stating that photosynthetic lifeforms require photons to be in any specific alignment for use, but if you guys can point me to articles which speak to the concepts posted here (coherence for penetration, et al.), I'd be very interested in reading about them -especially regarding the clam's anticipated light patterns.

 

One of the factors giving MH lights their increased efficiency is their point-source origin of light. The parabolic reflector is inherently more efficient than reflectors in PC lights, as restrike can be minimized. It also results in fewer photons being lost outside the tank (notice the way flourescent lights illuminate the areas around the tank?) I was very convinced by the article I posted below regarding use of LEDs, as the quantum efficiencies they expect to be able to reach (nearly 100%!!!) are amazing. They're a point-source of light and operate at low temperature (due to quantum efficiencies). Like I said, I expect a big debate, but fully expect them to be accepted in reef aquaria in the next few years. I am a BIG fan of efficiency!

[printerdown01]

Ummm…. yes and no… the lighting is diffuse but only to a certain degree. The light from both MH and PC come out of the bulb at almost 360 degrees. It is the job of the reflector to catch the light that is headed towards the ceiling and walls and redirect it back into the tank (this is true for BOTH MH and PC). Yes MH send light out in the wrong direction too, since the light is put out in a cirlc and the tank is a rectangle a great deal of light is lost. The light that leaves the MH-reflector and PC-reflector combos go in the same direction… The light put off by a PC does not magically come from the bottom right of the tank!

Most the rest of it is coming at weird angles off the glass, hood, and reflectors

They are photons not magic beans, this is not guess work, this is very simple conceptual physics (they teach this stuff in high schools now a days ). This is however a concession I am most willing to make, the standard MH reflectors are much better at redirecting light than the standard PC reflectors! However, there are some reflectors out there for PCs that more closely emulate the reflectors for MH (check them out: a more effective reflector for PC bulbs )… The newer PC reflectors are more parabolic like their MH-reflector cousins: a tip though when using any reflector, spray/paint it with a flat white paint! The spectrum is slightly shifted by the aluminum reflectors (a flat white surface has less chromatic distortion –thank you NASA, cause I would have never had the $$ to run those tests!!).

 

Now to deal with the “PC light is spread out way beyond where it should be” myth… I don’t know if you have ever thought about it before (I hope, after reading your posts, that you haven’t thought about it for a great deal of time). But PC bulbs AND their new parabolic reflectors are shaped more like a fish tank… Why is this important you ask? So what? –good then you haven’t thought about it (you were beginning to scare me there for a while). Your beloved MH bulbs spread out light in a circle (try it, all point sources do, and by the way that word is only valid for a certain distance, i.e. the sun is a point source from earth, but is not when you get up close… -just a though). One of the BIG reasons that you are suspending them so high above the tank is because they have to have enough time to spread out to light up your tank (not to many people want a circle of light on the sand in the middle of their tank), they want to light the whole tank. Thus, you are in fact giving the MH time to become LESS of a point source, it looks a LOT like a point source to you in the room (kinda like the sun does to us on earth) but not to your fish (which are completely illuminated by the source) it looks very similar to PC. More on PC point sources thoughts: Have you ever walked into a room and been illuminated by PC and tried to find your shadow?? –It doesn’t exist, this is because of diffuse light… Have you ever looked in my tank and tried to find a shadow? –It’s easy, they are everywhere, under every object there is a shadow! This is because the light is coming directly down, and is actually not “relatively” diffuse (remember the sun is “relative” point source, but in all actuality it is pretty diffuse!).

 

Ok, now on to the BIG issue… Whether or not MH is actually a superior light… By superior I am ONLY referring to the intensity of the bulb. –The choice looks obvious, right.. MH! –Well guess again! I wasn’t going to post this because I figured that it would upset a lot of people who spent $200+ on their single little light (which packs a hell of a punch!). But since most of the “advance” reefers seem to be stuck in the old way of doing things (and not keeping up on their readings and technological advances), defending themselves with theory (which wouldn’t have to be theory if they took 10 min to look up the lighting specs which are made easily accessible by the lighting companies themselves) they would have made different choices. Sorry, but sometimes the most experience reefs can be the most incorrect! Why? …new technology… the old reefers (happens to me too) get stuck in the old ways of doing things, and don’t bother to investigate new technologies. And as soon as they hear an idea that could possibly defend their old technology, they quickly grab onto it like a life preserver in a storm –whether it makes sense or not. Often you will find people with 15+ years in reefing that will tell you “that keeping a tank under 50 gallons is suicide (or “not possible”).” This is simply because they failed to keep up with their reading! So here it goes, the simple facts (sorry guys, but they are facts) a 175W MH bulb puts out a whopping 14,000 lumen, while a 96W PC (white, not blue… explained later) puts off a mere 8,100… hmmmm… MH must be more powerful right! –Wrong… 175W is a lot more than 96W, so let’s scale them down in terms of lumen/watt the MH would then yield 80lumen/watt while the PC yields an 84.4 lumen per watt! Now, here is the REAL problem (not these fictitious, half cocked theoretical -when there is not scientific theory behind them- excuses) : Can one reasonably put 2x96W of full spectrum PC on a 10 gallon tank, still leaving room for at least another 96W of 03?? –I highly doubt it (could happen, if you built the most elaborate hood that anyone has ever seen)…. But it isn’t likely! So in the end MH must win right!?! …again yes and no… YES MH is a MUCH better choice for large aquariums, the 400W bulb produces 90 lumens/watt!! Which is just awesome!! This is much more powerful than today’s PCs (the bigger the bulb the larger the lumen/watt ratio, PCs have failed to make a big enough bulb)… However, WHO IN THE WORLD would want to strap 3x96W on to their tank!?!?!?!?!? Now, I like tanks that are bright but I think it is unreasonable to try and make your tank look like the house on Chevy Chase’s Christmas! Look, I swear, 9.6W per gallon of PC on a 10 gallon tank is PLENTY of light for clams!!! I promise that people have kept clams for EXTENSIVE periods of time on 2x28W of PC in a 10 (and no they were not bleached, they did not look sick, and the photons put out by the PC did not try to in a mischievous plot try to avoid them:

Only a small portion of it actually strikes the animals directly

:-D. As I stated before photos are not magic beans, they are quite predictable… If this were true about photons, it would also be true about the ones put off my MH –but it isn’t… Sorry for the bitter post, but it is a little aggravating that this sort of nonsense is being discussed on the advanced forum. I do not consider myself “advanced” in lighting but at least I can fall back on some decent scientific principals and a decent knowledge of what I would consider to be lighting BASICS! I am usually quite polite in my posts, as I was in my original post when I asked you guys to re-evaluate what you were saying (for the “quality” of light IS equal, and PC CAN IN FACT pack as much lumen/watt as MH). But saying it politely and ending with “I’m not a lighting expert,” only encouraged people to B.S. their way through lighting giving unreliable and erroneous advice! –it was just unreal! *and another thing that was unreal, is that people took these ideas -which go against simple scientific principals- and ran with them!! ...sorry, I just could believe my eyes (I feel like Dave here! lol, no offense to Dave, I love reading his info, he seemingly never gives advice that is full of B.S. and bad theory. It is always well researched and founded upon logic). And it is not just you guys, a lot of the "old reefers" are out there screaming about "diffuse light" but it doesn't make sense in the context of what we are dealing with!

 

–oh, and those of you worried about lux, it is not an issue, since you would be comparing tanks of the same size… Thus, the lumen would translate to the same surface area, making them perfectly relative figures. ...and I'll be watching the progression of the LEDs! I hope these get some serious use in aquariums in the future!

[Lunchbucket]

yikes. lot of info.

 

good post

Lunchbucket

[MKramer]

I'm not even sure where to begin here....

 

First, while freely admitting I am not a marine animal expert, and cannot vouch for their lighting requirements, I am quite a bit more confident in the area of physics of light. Having spent the last six years working on electro-optical sensors, radars, blackbodies, and columnated light test benches.

 

Second, my point was that MH is not inherently better than PC or any other tube light. More that it lends itself to better reflector design. Even if a tube light fixture is housed in a deep parabolic reflector, it only provides a 2 dimensional pseduo-columnation of the light. In the third dimension, travel direction is quite arbitrary. And that's in a deep reflector. Most of us use our tubes in reflectors that only cover ~180deg of the bulb. Where a MH pendant reflects a much higher percentage of the light emitted from the bulb, and pseudo-columnates it in all three dimensions. The fact that a filament bulb like MHs have a single-source allows for much better reflector design.

 

Sensors exist to detect the columnation of light. A very crude description would be to picture a 10x10 grid of photocells, with each cell being at the bottom of a rather long, light-absorbant tube. Only light coming straight down actually strikes the photocell. The light difference one of these measures just between a spherical and parabolic reflector is considerable. I can only imagine a 2D parabola would be considerably worse.

 

Whether this behavior exists in aquarium lighting isn't of question to me. The real question is whether there are animals that are sensitive to the difference. Some primitive eye structures, actually, worked almost exactly as these columnation sensors do. I wouldn't find it all that far-fetched for other light-sensitive biological functions to have similar constraints. That's what I would like to find more research on.

[MKramer]

Another interesting thing to consider is polarity of light. Is it possible that some chloroplasts or other photo-receivers are incapable of using light with certain polarities? I'd have to do some digging to know for sure, but possibly either type of bulb can produce circular or other non-laminar photon wave polarities. It's another possible physical difference between the types of light the two bulb types produce.

[tinyreef]

printerdown,

 

i think you're brushing off the light diffusion issue too easily. the drawback to PC's as you yourself alluded to is the area they cover. you could fit about 4x96w pc over a 4' tank. that provides a significant amount of light over the whole tank, relatively evenly. 2x175w mh's pack less (wattage-wise) light over the entire tank but much more directly beneath the fixtures, targeting the livestock. pc's would be fine for a carpet anemone that coverd the entire tank but not for one that was 12"x12".

 

the thread started as a question on clams. the two things mkramer is leading to (but he lost me on the polarity ??? ) is having the correct light spectrum (i.e. energy) and photon quantity (~lumens). that is what needs to be addressed for the symbiont algae when discussing the light requirements. however a true discussion really needs the physical parameters of the system (distance from livestock to light source). pc's are a very good light source but they cannot generate the light intensity of mh's over the same area being targeted. lux may be a better measurement to be used but also should be coupled with energy units (mE).

 

pc's and vho's had preference for a while until the mh's spectrums were developed past the <5000K mark. that's when i started thinking about going mh again.

[printerdown01]

…sorry but I’m not really sure whether you are agreeing or disagreeing (it actually sounds like you are clarifying??)… From you word choice and general tone, I totally thought that you were attacking what I said, but as I read though your post, you had reiterated what I had stated earlier :

a concession I am most willing to make, the standard MH reflectors are much better at redirecting light than the standard PC reflectors

–so if this was an argument, I think we agree…well at least in the first part of your post, and then you went on about sensors that measure the degree of columniation of the light –which I found very interesting… I too would be intrigued to find out how close chloroplasts mimic these light sensors. I would imagine that they are not extremely close, as it would make for an inefficient design as light, in the ocean, comes from many different angles. Yes I know most coral reefs are located on the equator, where the sun is directly overhead… but it is only directly overhead at noon… not to mention the fact that the waters surface is quite good at scattering light (strobe effect, relative to something the size of a organelle). Is it possible that there is some mechanism that some corals have developed to take advantage of light coming from a single angle…? Absolutely! But given the fact that the bends at the ocean’s surface refract light so much and the fact that the sun rises and sets (yielding almost, but not quite 180 degrees of light angles though out the day) I don’t think it would be very efficient. *note MH too is refracted quite a bit when it hits the surface, which is why you can see the ripple effect on the bottom of the tank (trying to make it clear that I am NOT saying that MH sends light straight to the bottom while the sun gets refracted, they would both obviously act in the same manner). Oh, also, Mkramer, I was NOT attacking your post, save the two comments I had extracted from it (which I felt were a bit misleading). Unfortunately, they just happened to be the only quotes that I used when making my points –it was by no means intentionally done that way (your last post just happened to be sitting at the bottom of my screen while I was writing this, and thus it was easy for me to copy and paste from).

Perhaps I AM dismissing the diffusion aspect too quickly, but it seems illogical to me to assume that the light will come from a direct overhead source in the ocean (if you have been diving and looked up, you will notice a flaw in this idea). -perhaps this is why I dismiss the idea of scattered light being a problem so quickly...

 

Kramer do you by chance work a Pacific Wave?

[tinyreef]

i always thought the stobe-effect from the point of light emission was more aesthetic than utilitarian but i recently saw an article (i have no idea where now, don't laugh you will get old too) that notes it also has a magnifying effect (more than 2x sunlight?) ??? someone posted a link to it within their post (maybe on rc?).

 

i don't dive but i thought when you look up you DO see a light point versus a diffused light. i thought diffused light occurs at the lower depths (>10m). i assumed we were talking about the more popular and available tridacna clams.

[MKramer]

Heh, I'm not sure if I was agreeing or disagreeing either. Babbling, maybe?

 

Actually, I think your point about the motion of the sun throughout the day really invalidates the idea that clams and SPS need directional light. Who knows, there might be other animals out there that do, but given that these critters don't follow the sun, it would really seem like it's not the case for them.

 

I agree that recent anecdotal evidence seems to indicate that PCs and other flourescents are working in Clam & SPS tanks. Yet, as the entire premis of this thread states, "popular" opinion is still that MH are required. I have just been trying to tally what the possible difference between the typews of light sources are. The diffussion is one, but I think you've done a good job of ruling that out as a possible culprit.

 

Polarity is another, but I've never heard of an animal who was polarity-sensitive. However, sunlight creates light of all laminar polarity angles, plus circular and a few other oddball waveforms, where lighbulbs tend to strongly favor laminar polarities. So it's a possibility, just an unlikely one.

 

Spectral composition could be another possibility. I've seen spectral output graphs for many flourescents, although I can't seem to locate any for MH at this moment. Maybe it's possible that MH bulbs provided a significantly different spectral output than equivalently-colored flourescents. This could explain why people may have had problems with flourescents 10 years ago, yett hey seem to work fine now: an improvement in spectral output of the flourescent bulbs. Since Kelvin ratings don't really mean squat for non-incandescent bulbs, it would really take a side-by-side spectrograph comparisons to determine how close the two types are in output.

 

Just ideas. Sorry if things had started to degenerate into a nit-pick fest.

[Brianc_4]

I do not want to get pulled to far into the discussion, because I will quickly be in over my head. But the following link is the best I have ever seen on how to take care of clams Blue light clams

[tinyreef]

lol! i love clams too! oysters...mmm

 

now you've got me thinking of clam strips and stuff. X) with tartar sauce (drool)

[printerdown01]

You do bring up some interesting points, especially with polarity and flourescent spectrum issuse... It is quite possible that polarity is an issue, though I have never thought of it before... The coloration of softcorals is often a result of a natural "sunscreen." This sunscreen is, in the majority of cases (don't know of one that it doesn't hold true for, but I'm sure that somewhere out there exists an exception) is actually in tiny rows!! Is it possible that this could be their attempt to polarize light?? I dunno, I too think it is unlikely, but it is a cool thought, that I certainly wouldn't dismiss!! For if this is true, is it possible that other corals that do not have this built in sun screen (theorized polarizer -by myself, and probably only by myself) need a light that has a more polarized light... obviously perfect polarization would be out, since water has billions of tiny floating particles, but perhaps it needs to be "more" polarized?

 

Also you touched on another issue that is a problem with flourescent bulbs. The spectrum begins to shift over time, which is why it is suggest that one should replace a PC bulb every 6 months (rather than waiting until 12 months or so when it burns out!). They have been getting better over the years (and apparently PCs are a lot better than the old flourescents...), but this is certainly an issue to contend with!

*Hey, don't worry if you nit-pick... That is what an Advanced Forum should be for hehe

[Goofnut]

heh :-) Sorry if I sent you into a tailspin, printer... I know this is a "Holy War" (lighting, that is!) but I didn't intend to upset anyone.

 

My thoughts on the issue were in regards to how nature seems to operate. Many plants position their leaves so that photons impact them perpendicular to the leaf surface. In essence, they "follow the sun" during the daytime. I'm quite sure that they could survive with a less than optimal (diffuse) light source, but nature has its way of selecting increasingly efficent processes for life, which is most likely why this behavior came about. I haven't done/ready any studies on this concept (at least not since High School) but I believe it's due to the necessity of the plant to have the photons hit their chloroplasts at specific angles for optimal productivity.

 

Perhaps clams have a similar function? Maybe they are able to align the surfaces of chloroplasts in their mantles so that they don't have to physically reposition their bodies to take advantage of the varying angles of incoming sunlight throughout the day. I'll have to research that, as I'm intrigued now. It's just a thought, and I'm not even sure that this is the case. Maybe plants do it because the chloroplasts are fixed in position in their cells. It's possible (again, I haven't read anything to support/contradict this, yet) that the "loose" symbiotic algae in the mantle of the clam can dynamically position themselves independent of the operation of the clam to accept incoming photons in the most efficient manner. In essence, the algae COULD follow the angle of the sun throughout the day. If anyone has information about this theory of mine, please send it my way :-)

 

If all of the above held true, it would tend to support the position that photons oriented in a columnar fashion provide for more efficient photosynthesis than "diffuse" light. I'm not a physics major, so I'll stop my babbling... but I'd like to hear others' thoughts on this :-P Thanks for yer time!