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Food Production By Design, Using A Refugium To Produce Food For Reef Inhabitants.
By Ronald L. Shimek, Ph. D.
Introduction:
In the first article of this short series, I introduced the concept of producing food for one component of the reef aquarium system, the sessile suspension-feeders, by feeding the organisms living a second component, the sand bed. This indirect or "ecosystem" method of feeding is beneficial for three reasons.
- First, it produces live food for organisms that have evolved to eat live food.
- Second, it provides food continuously, and many coral reef organisms, including many corals are adapted to feed more-or-less continuously.
- Third, it "automatically" provides a way to utilize excess or uneaten food from the normal tank food, and in doing so, it maximizes efficiency and minimizes cost.
However, the sand bed is not the only reef aquarium component that may be utilized in this manner. Many aquarists have discovered, in one way or another, the concept of the refugium, a predator-free area that may function to produce animals that are food for other aquarium animals. Such refugia are not difficult to establish, and they may become a very important part of the aquarium system. They provide a way of producing a different type of food than does the sand bed. The food exported from the refugium to the main tank is typically larger and more mobile, and is more often eaten by fish rather than by sessile invertebrates such as corals.
The Concept and Construction:
It may be argued that coral reef aquaria are miniature examples, microcosms, of the real world. However, if they are, the view of a natural reef that they present is one seen through Alice’s looking glass. Such aquaria are typically full of small, immature, or stunted corals, and the density of all coral life is often much higher than in the natural world. Additionally, the concentrations of fishes and many other animals are also maintained at high levels that have no parallel in nature.
By and large, the animals maintained in coral reef aquaria are predatory, and in many systems they have the potential of literally eating themselves out of house and home. In general, aquarists seem to realize this and attempt to feed the animals, although often the amounts fed are unrealistically low for good animal welfare. In addition, the foods chosen to be fed are often inappropriate simply because many of the natural foods, or even reasonable analogs of the natural foods, are not available. Faced, first, with this starvation or semi-starvation regime, and second, with a normal feeding behavior that results in continuous feeding, the aquarium animals respond by eating anything that they can catch that looks, smells, or seems like food. The predation pressure in many tanks is often such that some of the common beneficial detritivore and herbivore populations are kept cropped to low densities. Generally, these prey populations are not destroyed, but rather kept small and the animals are often hidden. The animals become nocturnally active or they are evident only in those areas where the predators are excluded. This latter point was evident to several aquarists, who more-or-less simultaneously "invented" the concept of the refugium in the mid-nineteen nineties to ensure the survival of these beneficial animals.
Recognizing that most of the aesthetically desirable aquarium animals, such as corals and sea anemones were predatory would seem like an easy task, but it certainly didn’t seem to be. In the early stages of the aquarium hobby, misguided aquarium "authorities" spread the word that although some aquarium animals such as the fishes needed to be fed, virtually nothing else in the tank could, would, or should eat. The rationale for this point of view was based on the knowledge that many aquarium animals, such as corals, contained internal symbionts called zooxanthellae. Zooxanthellae are unicellular microalgae belonging to the group called the dinoflagellates. While most dinoflagellates are free living, water-borne, micro-organisms, a few types have developed the symbiotic life style where they live inside of their hosts. In such an environment, they are protected from environmental problems. In turn, when these small algae are found associated with animals, they may produce much of the daily sugar or metabolic energy requirement needed by their hosts.
Zooxanthellae may actually provide sufficient cheap carbohydrates that all of the hosts’ sugar requirements are met, and the host really doesn’t need to feed to stay alive. However, as sugars are only carbohydrates, and carbohydrates are not used to make tissues, the coral hosts cannot grow, repair injury, or reproduce using just the photosynthetic production of the zooxanthellae.
Around the middle of the last decade, many hobbyists finally realized that for their animals to grow, they needed to be provided with high protein foods. One way of doing this was to feed the corals and other zooxanthellate animals directly. A second way was to feed the tank, as described in the first article in this series, Food Production By Design, How A Deep Sand Bed Can Produce Food For Reef Inhabitants. A third method for providing protein-rich food exists. It is a way that is particularly useful when the aquarist is trying to maintain or raise animals that need food larger than either bacteria, or protozoans, or invertebrate larvae. This way is specifically useful when the necessary food must be either continually added or must be alive. That third way, of course, is to set up a refugium and to let the refugium do the feeding.
For once in a hobby replete with garbage terms, such as "sps, lps, and protein skimming" which really mean nothing, the term "Refugium" is quite descriptive, and apt. A refugium is a separate tank or portion of the main tank that is a refuge from the many predators in the aquarium system. Most of the time, the predators that need to be excluded are fishes, shrimps, and crabs. These predatory animals will eat a lot of the smaller animals in the tank, and as reef tanks tend be over populated with the predators, the smaller animals are continually at risk. Although many of these smaller animals are quite beneficial to the reef aquarium system, the hobbyist often tends to see them much as their predatory pets do; as food for those pets.
If these animals, mostly small crustaceans such as amphipods, harpacticoid copepods, and mysid shrimp can be protected from excessive predation, and if they are provided with sufficient food, they reproduce very rapidly. The offspring from this reproduction are highly nutritious food for most reef predators, which, of course, is why these animals need to be protected in the first place.
Given a place of safety from predation, all of these types of animals can reproduce plentifully and grow rapidly. As an example, many harpacticoid copepods produce eggs that hatch in a day or two, with the adult stage being reached within a couple of weeks. This means the time between successive generations is very short. The adults may live for several months to a year or more with each female producing a batch of 20 to 30 eggs per week. The offspring produced from those eggs can be reproductive in two weeks, followed by their offspring in two more weeks, and then two weeks later their offspring, and in two more weeks.…
Well, I think the reader will realize the number of copepods that may be produced in an aquarium tank may be astronomical. And this is definitely "a good thing." Harpacticoids are small bugs, and they and their larvae are a nutritious and very important food for such predators as small fishes, and small mouthed corals. Many fish are specialized to eat them, and may be very adept at picking them off, explaining the need for the refugium.
Slightly larger, but still small, crustaceans, such as mysid shrimps and amphipods reproduce equally well in refugia. As they are larger than the harpacticoids, their generation time is correspondingly longer. Amphipods and mysids don’t release their eggs into the sea, or aquarium, in this case, to develop without parental care. Rather the females are good parents, caring for their offspring during early growth and development. The females carry the developing embryos in a pouch on their ventral surface. Here they protect the eggs, and care for them until they are fully developed, but sexually immature juveniles. Once the eggs have hatched, the juveniles tend to disperse or spread throughout the habitat. This dispersal behavior makes both mysids and amphipods ideal animals for refugia. The adults remain well protected and are, in effect, baby factories, producing offspring continuously as long as they have sufficient food. The offspring help maintain the refugium populations, and disperse out of the protected areas to become either food or detritivores for the main tank.
By Ronald L. Shimek, Ph. D.
Introduction:
In the first article of this short series, I introduced the concept of producing food for one component of the reef aquarium system, the sessile suspension-feeders, by feeding the organisms living a second component, the sand bed. This indirect or "ecosystem" method of feeding is beneficial for three reasons.
- First, it produces live food for organisms that have evolved to eat live food.
- Second, it provides food continuously, and many coral reef organisms, including many corals are adapted to feed more-or-less continuously.
- Third, it "automatically" provides a way to utilize excess or uneaten food from the normal tank food, and in doing so, it maximizes efficiency and minimizes cost.
However, the sand bed is not the only reef aquarium component that may be utilized in this manner. Many aquarists have discovered, in one way or another, the concept of the refugium, a predator-free area that may function to produce animals that are food for other aquarium animals. Such refugia are not difficult to establish, and they may become a very important part of the aquarium system. They provide a way of producing a different type of food than does the sand bed. The food exported from the refugium to the main tank is typically larger and more mobile, and is more often eaten by fish rather than by sessile invertebrates such as corals.
The Concept and Construction:
It may be argued that coral reef aquaria are miniature examples, microcosms, of the real world. However, if they are, the view of a natural reef that they present is one seen through Alice’s looking glass. Such aquaria are typically full of small, immature, or stunted corals, and the density of all coral life is often much higher than in the natural world. Additionally, the concentrations of fishes and many other animals are also maintained at high levels that have no parallel in nature.
By and large, the animals maintained in coral reef aquaria are predatory, and in many systems they have the potential of literally eating themselves out of house and home. In general, aquarists seem to realize this and attempt to feed the animals, although often the amounts fed are unrealistically low for good animal welfare. In addition, the foods chosen to be fed are often inappropriate simply because many of the natural foods, or even reasonable analogs of the natural foods, are not available. Faced, first, with this starvation or semi-starvation regime, and second, with a normal feeding behavior that results in continuous feeding, the aquarium animals respond by eating anything that they can catch that looks, smells, or seems like food. The predation pressure in many tanks is often such that some of the common beneficial detritivore and herbivore populations are kept cropped to low densities. Generally, these prey populations are not destroyed, but rather kept small and the animals are often hidden. The animals become nocturnally active or they are evident only in those areas where the predators are excluded. This latter point was evident to several aquarists, who more-or-less simultaneously "invented" the concept of the refugium in the mid-nineteen nineties to ensure the survival of these beneficial animals.
Recognizing that most of the aesthetically desirable aquarium animals, such as corals and sea anemones were predatory would seem like an easy task, but it certainly didn’t seem to be. In the early stages of the aquarium hobby, misguided aquarium "authorities" spread the word that although some aquarium animals such as the fishes needed to be fed, virtually nothing else in the tank could, would, or should eat. The rationale for this point of view was based on the knowledge that many aquarium animals, such as corals, contained internal symbionts called zooxanthellae. Zooxanthellae are unicellular microalgae belonging to the group called the dinoflagellates. While most dinoflagellates are free living, water-borne, micro-organisms, a few types have developed the symbiotic life style where they live inside of their hosts. In such an environment, they are protected from environmental problems. In turn, when these small algae are found associated with animals, they may produce much of the daily sugar or metabolic energy requirement needed by their hosts.
Zooxanthellae may actually provide sufficient cheap carbohydrates that all of the hosts’ sugar requirements are met, and the host really doesn’t need to feed to stay alive. However, as sugars are only carbohydrates, and carbohydrates are not used to make tissues, the coral hosts cannot grow, repair injury, or reproduce using just the photosynthetic production of the zooxanthellae.
Around the middle of the last decade, many hobbyists finally realized that for their animals to grow, they needed to be provided with high protein foods. One way of doing this was to feed the corals and other zooxanthellate animals directly. A second way was to feed the tank, as described in the first article in this series, Food Production By Design, How A Deep Sand Bed Can Produce Food For Reef Inhabitants. A third method for providing protein-rich food exists. It is a way that is particularly useful when the aquarist is trying to maintain or raise animals that need food larger than either bacteria, or protozoans, or invertebrate larvae. This way is specifically useful when the necessary food must be either continually added or must be alive. That third way, of course, is to set up a refugium and to let the refugium do the feeding.
For once in a hobby replete with garbage terms, such as "sps, lps, and protein skimming" which really mean nothing, the term "Refugium" is quite descriptive, and apt. A refugium is a separate tank or portion of the main tank that is a refuge from the many predators in the aquarium system. Most of the time, the predators that need to be excluded are fishes, shrimps, and crabs. These predatory animals will eat a lot of the smaller animals in the tank, and as reef tanks tend be over populated with the predators, the smaller animals are continually at risk. Although many of these smaller animals are quite beneficial to the reef aquarium system, the hobbyist often tends to see them much as their predatory pets do; as food for those pets.
If these animals, mostly small crustaceans such as amphipods, harpacticoid copepods, and mysid shrimp can be protected from excessive predation, and if they are provided with sufficient food, they reproduce very rapidly. The offspring from this reproduction are highly nutritious food for most reef predators, which, of course, is why these animals need to be protected in the first place.
Given a place of safety from predation, all of these types of animals can reproduce plentifully and grow rapidly. As an example, many harpacticoid copepods produce eggs that hatch in a day or two, with the adult stage being reached within a couple of weeks. This means the time between successive generations is very short. The adults may live for several months to a year or more with each female producing a batch of 20 to 30 eggs per week. The offspring produced from those eggs can be reproductive in two weeks, followed by their offspring in two more weeks, and then two weeks later their offspring, and in two more weeks.…
Well, I think the reader will realize the number of copepods that may be produced in an aquarium tank may be astronomical. And this is definitely "a good thing." Harpacticoids are small bugs, and they and their larvae are a nutritious and very important food for such predators as small fishes, and small mouthed corals. Many fish are specialized to eat them, and may be very adept at picking them off, explaining the need for the refugium.
Slightly larger, but still small, crustaceans, such as mysid shrimps and amphipods reproduce equally well in refugia. As they are larger than the harpacticoids, their generation time is correspondingly longer. Amphipods and mysids don’t release their eggs into the sea, or aquarium, in this case, to develop without parental care. Rather the females are good parents, caring for their offspring during early growth and development. The females carry the developing embryos in a pouch on their ventral surface. Here they protect the eggs, and care for them until they are fully developed, but sexually immature juveniles. Once the eggs have hatched, the juveniles tend to disperse or spread throughout the habitat. This dispersal behavior makes both mysids and amphipods ideal animals for refugia. The adults remain well protected and are, in effect, baby factories, producing offspring continuously as long as they have sufficient food. The offspring help maintain the refugium populations, and disperse out of the protected areas to become either food or detritivores for the main tank.