With my fascination of reefs from watching tv, I have since been doing a ton of research (I knew I went to school for something!) on how to eventually have a nice reef tank. While I don't have the money to set it up yet, I do have the time to research how things actually work, and what will be needed for it. Lucky for me, a college buddy of mine was studying marine biology, and we have kept in touch ever since. He is now working with a group that is doing advanced research on coral reefs, and he was nice enough to give me some coral feeding info that they are putting together for hobbyists. He said I could post the info if I wanted, as it gets written. He also said they are trying to simplify it, to make it easier for us to understand (no complex numbers, references, researchers, etc.) So here is the first part... hopefully it will help you feed your corals, and mine too when I get some:
WHAT HAPPENS TO MOST CORALS: Reef aquariums are probably the most amazing thing you can have in your living room, and they really impress almost anybody, even if the tanks have only fake plastic corals. But reef tanks owners themselves are only impressed if they are successfully keeping real corals, which means of course, that the corals are not dying. Further, reef tank owners are even happier when their corals are actually growing and getting larger. The happiest moment for some hobbyists is when their corals are reproducing and showing up in new spots all over the aquarium where they never were before, just like corals do in the ocean.
In the real world of reef tanks, however, many corals die, or get covered with algae; they don't grow much (compared to the ocean), and hardly ever reproduce in remote spots in the aquarium (except for mushrooms, etc). If the corals grew like they did in the ocean, a three year old reef tank, started with only frags, would be packed to the glass and sticking out of the top from just the growth and reproduction of those original frags. Some hobbyists do know how to grow some corals, but they do so with lots of experience and equipment. No hobbyist, however, has been able to keep all coral types alive, much less keep them all growing and reproducing. So this info is designed to show you why this is, and maybe for the first time, to change it for the better.
CORALS NEED FOOD: If I were to tell you that I just bought a fish that lives on sunlight alone, and does not need food, you might be disappointed that someone lied to me at the fish store. But this is how many reef hobbyists think about their corals; they think that corals live on light alone, and that the corals do not need feeding. This is exactly the opposite of how it really works, and is the reason that their corals do not reproduce, grow, or even stay alive in some cases. In the ocean, there are no (zero) corals that live on sunlight alone. There are, however, corals that live on food alone, and which don't require sunlight. So, what exactly is this food that corals eat?
Corals eat PLANKTON. And the more plankton that is flowing in the water, the more that ALL the corals will grow. This is not the case with light: Corals need various amounts of light, but they will not grow more if the light increases past a certain point. With plankton, however, there really is no limit to the growth. Corals grow faster in the ocean when there is more plankton, and they grow slower when there is less. But most hobbyists have very little plankton in their tanks, if any at all, so sometimes the best they can hope for is that it's enough to keep the corals alive. Some hobbyists will mess around with the lighting, thinking it is the cause of slow growth, when actually it is just the lack of food.
WHAT PLANKTON IS: Plankton is the stuff that floats in the water. It's the stuff that looks like dust or dirt, or like little bits of trash. The bits can sometimes be so small you can't see them, or they can be as large as a pinhead. And they can be either alive or dead. The important part is, they FEED your corals. Yes, corals eat both the living AND the dead stuff that floats in the water. Here are some details on the types of plankton:
Zooplankton: These are little living animals, mostly little pods. Just remember "zoo", as in animals at the zoo. In the ocean, most of the zooplankton is copepods, which are as small as a grain of dust, or as big as the point of a pencil. Other zooplankton are rotifers and mysis. Ocean reefs are packed with zooplankton. Zooplankton is the major food of corals, and many small fish too (many baby fish eat only zooplankton).
Phytoplankton: Phyto mean "plant", and these tiny things are microscopic bits of plants that float around the top part of the ocean (about 300 feet deep, across 70 percent of the earth). They are actually algae, and they are the most important living things on the planet. They are 90 percent of all living life in the ocean (besides bacteria); they feed everything in the ocean, and they produce all the oxygen that you breath. Without phytoplankton, everything on earth would die (except maybe bacteria). Phytoplankton are so small that you cannot see even billions of them. Matter of fact, the crystal clear reefs that you think are "pure", are actually loaded with huge concentrations of phytoplankton in the water.
Detritus: Pronounced similar to "just-TRY-us". Detritus is stuff that used to be alive (zoo, phyto, fish waste, coral waste), but now is dead. Reefs have more detritus floating around than any other part of the ocean, so detritus is a major food for corals.
Bacteria: The number one life form on Earth, including in the ocean. Bacteria is very active on ocean reefs, and it feeds lots of corals, although not as much as zooplankton.
HOW FAST DO CORALS GROW IN THE OCEAN: Fast-growing branching corals, like staghorn acropora, can grow 8 to 10 inches (20 to 25 cm) per year in length. Here is a sample report:
Geoscience Research Institute
http://www.grisda.org/origins/06088.htm
"Most polyps at 66 cm from the tip will be approximately 7 yr older than polyps at 3 cm from the tip" [this equates to a linear growth of 9 cm per year; a frag that is small today would be 18 cm in diameter (7 inches) in one year.]
"Sewell (1935) reported 280 mm/year [11 inches] in the Andaman Islands in the Bay of Bengal, and Verstelle (1932) reported a maximum rate of growth of 414 mm/year [16 inches] in the Celebes."
"The fastest growth rate reported for any coral is the staghorn species Acropora cervicornis. Lewis (1968) found in Jamaica a maximum rate of 264 mm/year [10 inches]. Shinn (1976) studied the growth of this species following destruction in a hurricane near Florida. He estimated linear growth rates of 100 mm/year [4 inches]. He also found that because of the branching habit (several new branches added to a single previous one), much more than the linear growth of a single branch is involved in establishing a dense stand of this coral. Under these branching growth conditions, carbonate production [growth] would be more geometric than linear, and could contribute further to the carbonate mass [size] of the reef. Gladfelter, Monahan and Gladfelter (1978) report rates of 99 mm/year [4 inches] for Acropora palmata in the Virgin Islands."
And here is another study:
Growth Of Acropora Pulchra in Bolinao, Pangasinan, Philippines. Proceedings of the Fourth International Coral Reef Symposium, 1981:
"If mean monthly growth rates for all [test] sites are averaged, they can be extrapolated to obtain a mean annual growth rate of 18.1 cm/year [7 inches] for Acropora pulchra. 22.58 cm/year [9 inches] was obtained for the same species at Yap Island in the Western Pacific, in a study that covered only the cooler [slower growing] months of October to December."
Mean growth rates of Acropora pulchra control colonies:
Date -- Mean Growth Rate (cm/month)
10/80-12/80 Site A: 1.8 Site B: 1.6 Site D: -
12/80-01/81 Site A: 2.3 Site B: 2.0 Site D: 1.5
02/81-04/81 Site A: 1.4 Site B: 1.3 Site D: 1.2
04/81-05/81 Site A: 0.6 Site B: 0.8 Site D: 0.6
HOW TO FEED YOUR CORALS: To achieve growth like in the ocean, corals need to be fed like they are in the ocean. Most all corals do use sunlight, and this is called Autotrophic feeding. Auto means "self", and Trophic means "feeding". Sure enough, the corals use the sunlight to "make" some energy for themselves. Most all aquariums have enough light, especially reef tanks, so fortunately this is not a problem. Most of the energy from sunlight, however, is only used to keep the corals alive; very little is used for growth and reproduction, which is what we want.
The second type of feeding is call Heterotrophic. Hetero mean "different", and sure enough, corals also eat food that they don't make themselves. Matter of fact, this is how corals get most of their food, especially when it comes to growth and reproduction. This food can be any of the plankton listed above: Zooplankton, phytoplankton, detritus, and bacteria. It's the zooplankton that does most of the feeding; and since zooplankton is actually alive, the corals are said to be "predators" of the zooplankton. It's kind of weird to think of corals as predators, but if you ever get a chance to use a microscope to watch coral polyps (especially SPS) use their chemicals to zap and eat pods, you'll understand. A polyp senses a pod (some polyps actually chase pods), and then it stings the pod with chemicals; it then wraps around it with a sticky net and pulls the pod into the "stomach" of the coral where the pod gets digested over the next couple of hours.
This digestion part is important, because a polyp cannot eat again until the initial food is digested. This is why you want to supply food to corals 24 hours a day, especially at night, which is when most feeding occurs in the ocean. If you just try to target-feed your corals by blasting them with (any kind of) food, only the first few particles that hit the coral will get eaten and digested, and all the rest will go to waste. So if you are going to limit coral feeding to certain times, make sure it's at night, or else the polyps won't catch enough. But by far the best technique is 24 hours a day, just like they eat in the ocean.
SUMMARY: With some slight changes in your feeding techniques, you can multiply the growth of your corals many many times, and even get them to multiply/reproduce in remote parts of the aquarium where they never were before. And maybe you can also help save corals from extinction, starting with the Acropora cervicornis "Staghorn Coral", and the Acropora palmata "Elkhorn coral", which are already almost gone (95 percent extinct, due to environmental changes) and are not expected to be around much longer in the ocean.
Lastly, here are two plankton videos that we found on youtube, which do a pretty good job of describing what plankton is:
http://www.youtube.com/watch?v=LuXMz3j9E8k
http://www.youtube.com/watch?v=A9AKf6OnuPg
And here are pics of the corals talked about:
