Coral Feeding

[lduncan]

All this talk of feeding pretty much comes down to where corals get their nitrogen. So what can corals feed on to get this nitrogen?

Dissolved inorganic nitrogen(Ammonia nitrate etc.), bacteria, microplankton.

Starting from the start how do these nutrients enter the tank? Well the bulk of it is going to come from you putting it in there. Once the food is in there, what happens to it? Much of it is eaten by fish and animals in the tank. Some of it may be skimmed out. Some may get trapped in crevices and be broken down by bacteria. All animals produce waste. So once the fish digest the food they produce ammonia and crap, esentially detritus.

Now say you have two identical tanks, one with sand, one without sand, and you feed them equally. Logically, the mass of nutrients in the tank is going to be the same. What some people seem to be saying is that the tank with the sand somehow has more food available, and somehow is more benifical to corals? How can this be? It's impossible, unless the sand is magically creating matter. Adding calcium carbonate to the bottom of the tank does not increase the ammount of food available to corals. In fact it may result in the opposite.

Getting back to detritus created by both rocks, fish crap, coral mucus and other animal waste. This stuff is basically bacteria a collection of bacteria. Corals actively farm bacteria in their mucus for their own consumption, and bacteria in general are a good food (nitrogen) source for corals.

The moral of this long nitrogenous trail is that corals must feed either on bacteria or on plankton or on both to maintain enough amino acid input to live and grow.

Corals not only use their mucus to trap bacteria, but the coral mucus also serves two other purposes. First, it is an incredibly good growth medium for marine microbes resulting in and the surface of corals containings bacterial communities with densities far in excess of the already significantly high levels in the surrounding waters and benthos. Second, and; coral mucus is a primary contributor to some kinds of detritus, where – the particulate aggregates are held together by coral mucus with levels of bacteria two to five2-5 times higher than in particulates without the presence of coral mucus. These aggregatesd not only provide food for corals, but for all manner of particulate filter feeders, a category – that encompasses directly or indirectly just about every living animal on the reef. Furthermore, these microaggregates contain a tiny recycling community where nutrients themselves are concentrated 2-3 times higher within the aggregates than in the surrounding water. These energy “packets†are extraordinarily important, both to individual organisms and the entire ecology of the reef.

Increasing evidence points to the idea that the microbes on the surface are not only acting directly as food, but are involved in the production of specific compounds either in limited availability or unavailable by other means. The bacteria may provide these as “leaky†fluids resulting from their own metabolism. Additionally, nitrate reduction or nitrogen fixation is occurring, and the action of such microbes may provide an important source of inorganic nitrogen to both coral polyps and zooxanthellae.

This is interesting from Dr Ron:

All of this excess food, processed food, and detritus drifts through the water of an aquarium for an indeterminate time and may, in fact, go to feed coral and other suspension-feeders directly, but most of it reaches the bottom and enters the realm of the deep sand bed organisms.

What would happen if you didn't have sand, and could keep this stuff in suspension and not let it settle? Wouldn't it stay in circulation in the water column available for the corals to feed on?

What happens when this detritus get stuck in the sand? It prodvides a rich habitat for critters, pods etc. What do they feed on? The same bacteria ladened detritus which has come from the rocks, fish and corals. So so far there is no magical increase in mass of food in the tank. So far, all the sand be has done is remove some of it from general circulation in the tank. Corals can't get that portion of it now.

So now in the sand with all those different types and sizes of pods, worms, algae, and snails, you somehow need to get those to the corals? You will get a bunch of them venturing out at night and get consumed by corals (assumung they are the right size for the coral, aren't too strong, and the coral actually digests them etc)

Now looking at the BB system for a minute. There is still the same amount of food in the system, but it exists as free floating bacterial infested detrital particulates. You don't have any sand to hold it, and you don't have massive algae, pod, worm, and snail populations to consume it and make it less available to the corals.

Sand beds can be considered an animal in themselves, and compete with corals for food.

So in virtually identical tanks which are fed the same amount, which one has more food available to the corals? One where it's at the bottom tied up in sand and critters, or the other tank which is floating free in the water as bacteria ladened detritus?

Also, remember that bacteria, weight for weight, are more nutritious than other critters like pods. Your looking at 10% in undeigestable shell, a lot of empty space, and also require a lot more energy to digest than bacteria.

Of the two sources, weight for weight, bacterial tissue contains more nitrogen than animal flesh

Sand beds actively try to convert bacterial mass, into critter mass. Surely this just makes life harder for corals? Some more stuff from Dr Ron:

Dissolved nutrients are really the food for bacteria, and the fecal material is rapidly colonized by bacteria. Both the fecal material and the bacteria on it may be food for other organisms, primarily sediment-dwelling animals.

All of this excess food, processed food, and detritus drifts through the water of an aquarium for an indeterminate time and may, in fact, go to feed coral and other suspension-feeders directly, but most of it reaches the bottom and enters the realm of the deep sand bed organisms. Here it is may be mobilized up in to the water column for one more times before all the nutrient value is lost.

The majority of the nitrogen budget for these animals comes from two sources, feeding on flesh and feeding on bacteria. Of the two sources, weight for weight, bacterial tissue contains more nitrogen than animal flesh ...

The moral of this long nitrogenous trail is that corals must feed either on bacteria or on plankton or on both to maintain enough amino acid input to live and grow.

Corals can either be fed directly or indirectly. Direct feeding is the placing of food directly on the coral's oral disk or in the tentacles. The animals then ingest the food. Indirect feeding is where the corals feed on materials in the aquarium water, but are not directly fed by the aquarist. The latter type of feeding can range from feeding on "left-over" debris or food from intentional feeding of other animals such as fishes, or it can be feeding on micro- or bacterio- plankton that are maintaining populations in the system.

Indirect feeding is often a whole lot easier, and it is really the only way to be feeding corals such as Acropora, Seriatopora, and probably Goniopora. These species will do well in brightly lit aquaria to boost the output from their zooxanthellae, but their nitrogen intake is probably best met by bacterioplankton in the system.

Bacterioplankton are a natural byproduct of an aquarium maintained with a good sand bed, high circulation, and a reasonable amount of live rock. Basic nutrient energy has to be added to the system by feeding, but the corals in this system are not fed directly. Rather the other tank inhabitants, such as fishes, larger-polyped corals or sea anemones are fed and their waste products and uneaten food fuel the bacterial populations of the system. Where sediment bacteria are healthy and water currents are sufficient, there will be bacteria in the plankton for the small polyped corals to feed upon. Additionally, there will be some dissolved organic material in the water for them to absorb.

He just seems to come to some weird conclusions. Why does he promote sand beds so much? (Financial interest maybe? His love of critters maybe?) His own writings suggest they're not all their craked up to be. I didn't even touch the other things which sand beds do.

Personally, I'll only ever use sand for aesthetic reasons. It's not a nutrient remover, nor a food creator. They just cycle and change stuff. Often not for the better.

Layton

[suphew]

An interested post, a want make a couple of comments. First and please don’t take this an attack, I know very little about the subject at hand.

You posted a lot of information but it is only based on what you have read and your own conclusions, not solid scientific research, that you have done, you aren't a marine biologist, yet you state your own unqualified conclusions as proven fact. While discrediting the findings of (as far as I know) qualified people. Don't say this to argue with you, but so maybe you understand why people are so quick to disagree

Personally, I'll only ever use sand for aesthetic reasons. It's not a nutrient remover, nor a food creator. They just cycle and change stuff. Often not for the better.

The secondly, and I know nothing about marine bacteria, but I do know that in fresh water there are many times the amount of bacteria living on surfaces that in the water. A sand bed has a huge amount of media and surface area, perhaps this explains why it works? Also my understanding of BB and suspending matter in the water was so that the skimmer is able to remove it? This would explain why in two identical tank, fed the same, one without sandbed, that the corals get more food with the sandbed. Because the sand bed puts it into a form the corals use (bacteria), where as in the BB it is skimmed out.

[chimera]

:lol:

[wasp]

He just seems to come to some weird conclusions.

Layton

Don't really buy that in this case. What weird conclusions? How weird?

Doctor Shimek is quite knowledgeable in his particular feild, I also don't buy the insinuation that he is only saying it for financial reasons.

You've made similar financial allegations against other people who don't hold the same views as you, better to just focus on the topic rather than these type of assumptions.

[lduncan]

Your right, I have no formal qualifications in marine biology. However, I can read what others write, as far as scientific findings go, then form my own conclusions on that.

However, to dismiss any conclusions I may have come to based on the information available, you have to come up with reasons why they don't hold up. Not having the relevant formal qualifications is not a valid reason.

The second question. Dr Ron can answer that:

All of this excess food, processed food, and detritus drifts through the water of an aquarium for an indeterminate time and may, in fact, go to feed coral and other suspension-feeders directly

The waste is already in a form which is edible to corals, coated in bacteria before it gets to the sand. It's that sand which dilutes it and makes it LESS useful, by packaging it up in the form of pods, which are required to leave the nutrient rich environment of the sand, into the water column, where some corals may be able to catch them, if they are the appropriate size, not too strong, and if they do manage to hold on to them, they have to spend more energy digesting, than bacterial detritus.

The fact is the sand doesn't just produce bacteria out of nowhere, ultimately the vast majority the food in the system comes from YOU putting it in there. In otherwise identical setups (matching imports and exports), a BB tank will have the same amount of food as a tank with sand. Only in the BB tank, there is more of it in a more digestible form for corals.

People forget that for detritus to get to the skimmer, it must have been floating in the water column, which means corals had at least some opportunity to grab it. If it's not in the water column, how are they supposed to get it?

Also the idea of BB is all about control, you have complete control over the system.

[wasp]

Not having the relevant formal qualifications is not a valid reason.

It might be, all else being equal.

What exactly have you read that Doctor Shimek is not aware of?

How many years experience do you have compared to him?

What of relevence did you study at Uni?

How much marine lab time do you spend compared to him?

[lduncan]

Wasp that's all irrelevant. How about a question relating to what I posted.

What don't you agree with?

Layton

[wasp]

What don't you agree with?

Layton

Saying his conclusions are weird for one.

How weird?

In fact to say the formal qualifications are irrelevant is weird. No?

[suphew]

I think if you re-read my post I you will find I didn't attack the information you posted based on your lack of qualification, but just how you stated your conclusion as fact, when in reality it was just your own unquailified views.

In otherwise identical setups (matching imports and exports), a BB tank will have the same amount of food as a tank with sand. Only in the BB tank, there is more of it in a more digestible form for corals.

The first part of this statement I agree with, however this isn't based in reallity, the reason for running BB is to suspend the matter in the water so it can be removed, therefore there aren't matching import and exports between BB and sand. The second half of your statement is purely based on the correctness of the first, so is therefore incorrect.

I think you are basing this all on two questionable assumptions, firstly that all thing's being equal, all the import will be either turned to food or will end up in the sand bed,if this is the case what is the skimmer doing? And secondly that water has the same ability to process food (i.e hold bacteria) that a huge volume of media does. If this were true then wouldn't we all run bioballs in our sumps or great wads of filter wool, for months on end?

[lduncan]

Don't really buy that in this case. What weird conclusions? How weird?

Ok here's what I find wierd. First he says that bacteria are better than pods for providing nutrients. Bigger bang for your buck.

Bacteria are a very good source of useable nitrogen, as the bacterial cells have a higher ratio of nitrogen to carbon than do either plant or animal cells.

Then he says that detritus is a good food source for this bacteria to colonise.

Fecal material is not waste material, but rather indigestible food, often with a sizeable component of digestive enzymes still active in it. As such it liberates a lot of dissolved nutrients. Dissolved nutrients are really the food for bacteria, and the fecal material is rapidly colonized by bacteria.

He then goes on to say that sand dwelling creature are a big competitor to corals for this nutrients:

Both the fecal material and the bacteria on it may be food for other organisms, primarily sediment-dwelling animals.

But then goes on to promote the use of sand as a food source:

With some foresight, and a little work a sand bed may be constructed and maintained that provides a significant amount of food for suspension-feeders in a marine aquarium. The key to such food production is the proper construction and maintenance of a deep sand bed, followed by the appropriate feeding of the tank with a variety of foods, but including specifically phytoplankton, and small particulate material. Such a system will provide sufficient food to provide much of the food necessary for the proper and balanced nutrition of coral reef animals.

To me that's just a weird conclusion. Using something which actually eats one of the most nutritious forms of food for corals (bacteria), and converts much of it into a form which is harder for corals to digest, and provide less nutrition.

Seems kind of backwards to me. Surely you want the food which is in you tank to be easy for corals to digest and nutritious? The habitat sand provides does the opposite, by Ron's own writing.

Layton

[lduncan]

The first part of this statement I agree with, however this isn't based in reallity, the reason for running BB is to suspend the matter in the water so it can be removed, therefore there aren't matching import and exports between BB and sand. The second half of your statement is purely based on the correctness of the first, so is therefore incorrect.

What matters is the amount of food in the water column, after all that's the only place the corals can get it from. Anything in the sand doesn't count they can't get it when it's there. So two tanks, one with sand, one without, exactly the same skimmers etc. Now imagine if both had the same mass of food floating in the water column (same amount of food in the water available for corals). The skimmer is going to remove a similar amount is it not? Even though there may be a lot tied up in the sand, that portion is irrelevant, they can't get it.

Food has to be suspended for corals to get it, if it's suspended the skimmer can get it too.

I think you are basing this all on two questionable assumptions, firstly that all thing's being equal, all the import will be either turned to food or will end up in the sand bed,if this is the case what is the skimmer doing?

See above, same food concentration, same skimmer output.

And secondly that water has the same ability to process food (i.e hold bacteria) that a huge volume of media does. If this were true then wouldn't we all run bioballs in our sumps or great wads of filter wool, for months on end?

What does it matter if it can hold the stuff. If it's holding it, the corals can't get it, so what's the point in having it there?

Layton

[suphew]

What matters is the amount of food in the water column, after all that's the only place the corals can get it from. Anything in the sand doesn't count they can't get it when it's there. So two tanks, one with sand, one without, exactly the same skimmers etc. Now imagine if both had the same mass of food floating in the water column (same amount of food in the water available for corals). The skimmer is going to remove a similar amount is it not? Even though there may be a lot tied up in the sand, that portion is irrelevant, they can't get it.

But that isn't what you said, you said "two identical tanks with matching imports and exports" not two tanks with the same amount of food in the water column. If the sand bed is as you say using food and not producing anything useful, then either imports have to higher or exports lower for the food in the water column to be the same.

What does it matter if it can hold the stuff. If it's holding it, the corals can't get it, so what's the point in having it there?

I'll admit my choice of word wasn't clear, maybe I should have used the word 'produce' instead of 'hold'. The point being there will be far more bacteria on a surface than floating in water, and a large % of the bacteria floating in the water would have infact come off the surfaces, not actually been produced in the water. Surfaces are a far better environment for bacteria to reproduce, this is why bio filters are filled with media and not just water :roll:

[lduncan]

But that isn't what you said, you said "two identical tanks with matching imports and exports" not two tanks with the same amount of food in the water column. If the sand bed is as you say using food and not producing anything useful, then either imports have to higher or exports lower for the food in the water column to be the same.

I didn't say the sand bed isn't producing anything useful. I'm saying it's taking a portion of the MOST useful stuff, and converting it to stuff which is not AS useful (lower nutritional value and harder to digest). It also makes less food available by trapping it. Removing it from the water column. It has to be in the water for corals to have a chance of getting it.

Are you saying that a BB tank exports more than a tank with sand, given same food input and same skimmer?

I'll admit my choice of word wasn't clear, maybe I should have used the word 'produce' instead of 'hold'. The point being there will be far more bacteria on a surface than floating in water, and a large % of the bacteria floating in the water would have infact come off the surfaces, not actually been produced in the water. Surfaces are a far better environment for bacteria to reproduce, this is why bio filters are filled with media and not just water :roll:

Well they don't produce any extra food. They convert existing food to different types of food.

It's not the surface that promotes the growth of bacteria, it's the conditions they are in. Bacteria live in broths, they aren't necessarily attracted to inert sufaces because of some need to hold on to something. Some go to the effort to create their own broths in environments which are otherwise hostile. Sometimes the broth exists already.

The reason why bio-balls and sand beds attract large bacterial populations is because they mechanically trap and therefore concentrate the very food which bacteria feed off. What if the food is never trapped on a surface? Well the bacteria don't care, it's all about the food and environment to them. They'll happily float around with their food.

Here's something from Eric on bacteria:

Coral reefs depend heavily on bacteria in all manner of action. The majority of bacteria in the water column are free living and feed on dissolved organic matter. These microbes will process the organic matter in the water with a 30-50% efficiency rate. Pelagic bacteria can double their populations within one tide change to respond to an increase in nutrient levels. Bacteria normally compose between 5 and 20% of the total biomass of plankton, either free living in the water column, or associated with particulate matter. This number represents an even larger planktonic mass than zooplankton. They are also responsible for up to 30% of the primary production of reefs.

Also, there has been a lot of focus on organic food sources. What about inorganic sources like ammonia, nitrate etc. These are not exactly in short supply in our tanks. Couldn't they be considered a large source for corals?

Layton

[cracker]

Sandbeds contain critters that break down "floating" matter, (Now that its in the sandbed), to extremely microscopic sizes more than just floating around can do.

Small critters are consuming, then crapping and smaller critters are consuming thaty crap and pooing mmore crap.

The breakdown of matter is similar to a compost heap.....

Think about it.

[lduncan]

What does it matter if it never leaves the sand bed and gets to where it's needed? If it's nutritional value is diluted, and takes more energy for corals to digest? Not to mention corals don't just feed on any critters. And some corals are less able to catch and hold onto all these critters than others.

So what about inorganic sources? Corals use these as well. They are abundant in our tanks.

Layton

[cookie extreme]

so why do lagoons have a much higher nutrient count then the reef edge? same ocean, same water, different corals but quantity wise the same! is it because of the sand lagoons have and reef edges don't? and why do these lagoons support "hard to keep" stonies?

[cracker]

CURRENT FLOW IS HIGHER ON THE REEF EDGE.

[cookie extreme]

CURRENT FLOW IS HIGHER ON THE REEF EDGE

true but wouldn't that mean that more "crap" ends up in the water colum and where is the crap going? on the beach, but even it does end up on the beach it should be visible in the water which it is! at night and then in very high amounts regardless if inner or outer reef.

[suphew]

So what about inorganic sources? Corals use these as well. They are abundant in our tanks.

Eric touches on this in his video on coral progation, according to him corals will use inorganic compounds but so do the zooxanthellae, because of the free food source their population increases causing the corals to go brown. For this reason he suggests low nutirant tanks and coral feeding. Not really any surprises there.

[suphew]

I didn't say the sand bed isn't producing anything useful. I'm saying it's taking a portion of the MOST useful stuff, and converting it to stuff which is not AS useful (lower nutritional value and harder to digest). It also makes less food available by trapping it. Removing it from the water column. It has to be in the water for corals to have a chance of getting it.

Personally, I'll only ever use sand for aesthetic reasons. It's not a nutrient remover, nor a food creator. They just cycle and change stuff. Often not for the better

So which does it do? is it not a nutrient remover, or is taking a portion of the MOST useful stuff.... that would be nutrients?

If it's nutritional value is diluted, and takes more energy for corals to digest?

Why is bacteria from a sand bed lower in nutritional value and harder to digest? I think the point cracker was making in his post is that sooner or later everthing ends up getting eaten by bacteria, which the corals can then feed on, what happens to pod pooh? what happens when pods die? Why do the nutrients have to be eaten directly by bacteria to be any good to for the corals, bacteria eat the same basic stuff, it doesn't mater who poohed or died to produce it.

Are you saying that a BB tank exports more than a tank with sand, given same food input and same skimmer?

Isn't that the whole point? Would anyone choose a BB over sand for any other reason? And I'll say it again, and try and make it simple, if you put something in, and something takes some of it out (like a sand bed) then you most end up with less coming out than you put in?? If you then take the sand bed out of the equation, so are no longer taking that extra bit out, them you must be getting more out at the end??????

[suphew]

Bacteria live in broths,

Will be checking my tank for broth, first chance I get.

The reason why bio-balls and sand beds attract large bacterial populations is because they mechanically trap and therefore concentrate the very food which bacteria feed off. What if the food is never trapped on a surface? Well the bacteria don't care, it's all about the food and environment to them. They'll happily float around with their food

Isn't this just what I suggested the sand bed does? collects nutrients and puts it into a nice concentrate , all ready to produce many times more bacteria, which then end up back in the water column

[lduncan]

so why do lagoons have a much higher nutrient count then the reef edge? same ocean, same water, different corals but quantity wise the same! is it because of the sand lagoons have and reef edges don't? and why do these lagoons support "hard to keep" stonies?

The wide variety of different corals that there are, have an equally wide spectrum of nutritional requirements, even within genus. The also have a variety of methods they can use to get these nutrients. Different environments go through cycles of varying length and at different times are in different state which may allow them to support corals which they may not at other points in their cycles.

You have upwellings at the reefs edge which are cyclic, providing sources of organic nutrients, then in periods of no upwellings you find the water higher in dissolved inorganic sources. Corals need to have a variety of sources for their nutrition, to cope with these cycles.

Just because they use one predominantly in a particular natural environment, doesn't mean it has to use it in our tanks, it may be easier or more convenient ways available.

Layton

[lduncan]

Eric touches on this in his video on coral progation, according to him corals will use inorganic compounds but so do the zooxanthellae, because of the free food source their population increases causing the corals to go brown. For this reason he suggests low nutirant tanks and coral feeding. Not really any surprises there.

Isn't that interesting. It's that what everyone goes to a lot of effort to avoid? Brown corals. Doesn't that show how much dissolved nitrogen is available in tanks, and how difficult it can be to keep it low enough? Maybe it does provide a significant source of nitrogen, even in the cleanest of tanks?

The question is how low is low nutrients? Is it possible to reduce dissolved inorganic nitrogen in our tanks to a level where it can't provide a significant source for corals?

Layton

[puttputt]

mmmmm bacterial broth

can i get bread with that

Isn't this a great hobby. So many different theories and so many great tanks using all of them.

[lduncan]

So which does it do? is it not a nutrient remover, or is taking a portion of the MOST useful stuff.... that would be nutrients?

I thought I explained that. Food (bacterial detritus) drops into it from above. Critters are able to reproduce in the safer confines of the sand. They feed on this bacterial detritus, producing an organism of lower nutritional value which itself produces waste, but it doesn't create more waste than previously eaten, it's not possible. Then it may or may not be possible for corals to eat some of these critters which reduces the availability even further. Corals are good at digesting bacteria, so good that researchers had trouble determining whether they do in fact eat them, as the time from collection to doing a gut analysis was long enough that the bacteria was unrecognisable (sometimes only several minutes), all they could find were partially digested pod shells.

Why is bacteria from a sand bed lower in nutritional value and harder to digest? I think the point cracker was making in his post is that sooner or later everthing ends up getting eaten by bacteria, which the corals can then feed on, what happens to pod pooh? what happens when pods die? Why do the nutrients have to be eaten directly by bacteria to be any good to for the corals, bacteria eat the same basic stuff, it doesn't mater who poohed or died to produce it.

The thing is that by actively encouraging other critters to feed on bacteria, you are reducing this proportion of highly nutritious coral food. Sure the sand bed supports bacteria, but it can't possible create more bacteria than the food your putting in allows. You put so much food into a tank, and say (just to keep things simple) it goes to either bacteria or critters. BB you have a lower critter populations, which means more of that food is going to end up being associated with bacteria which is an easy food source for corals. You put the same amount of food into a tank with sand, which has a high critter population so proportionally less of that food is going to be available to corals as high nutrition bacterial coral food, while the rest goes to supporting the critter populations, which may or may not be the right size and type.

Isn't that the whole point? Would anyone choose a BB over sand for any other reason?

It's not always the point. Depends how you want to run it.

But if that's what your saying, then you're supporting my claim that BB has more food available to corals.

For a skimmer to work, it requires the stuff to be floating in the water.

If a skimmer is removing more in a certain period of time, that means there is a higher concentration of food in the water.

If the same skimmer is not removing as much in a certain period of time, it means that there is a lower concentration of food in the water.

If putting sand in a tank reduces the skimmer output, doesn't that imply that it also reduces the available food in the tank?

Isn't the idea to have a high concentration of food available in the water so corals have access to it?

And I'll say it again, and try and make it simple, if you put something in, and something takes some of it out (like a sand bed) then you most end up with less coming out than you put in?? If you then take the sand bed out of the equation, so are no longer taking that extra bit out, them you must be getting more out at the end??????

:-? I've read that a couple of times I still don't see what you mean?

Layton