XIV. Difficult Coral - The Heterotrophic Reef Tank

This article discusses Heterotrophic Coral, Gorgonia & Precautions

 

     The vast majority of coral kept in the aquarium trade are considered Autotrophic, meaning that they in some way or another possess the capability to derive nutrients and energy from the environment around them. Some coral like LPS coral, supplement this autotrophic lifestyle by capturing prey to consume in addition to the energy it receives from photosynthesis. There are fewer corals available that are considered truly Heterotrophic. Heterotrophic coral requires the input of some form to obtain nutrients and survive. This means that all Heterotrophic coral must be fed in captivity or they risk starvation.

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Heterotrophic Coral

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     While few in number they are striking an example. The Dendronephthya, known for its neon contrasting polyps and branching tissue is a soft coral and Tubastrea, a bright orange coral LPS coral that sports bright yellow polyps are the two most commonly available heterotrophic coral. While Tubastrea is a great example of a coral whose dietary needs can be met in captivity, Dendronephthya remains a difficult challenge to import and care for properly. Both these corals require very high flow as they come from the depth where the current is very high. Neither of these corals seems to react to low light levels and I have seen Tubastrea kept under simple fluorescent tubes. Additionally, neither of these corals are particularly well suited to an ordinary reef tank due to unique requirements.

 

     Tubastrea is by far easier to keep than Dendronephthya. Spot feeding a Tubastrea several times a week with Mysis shrimp seems to be sufficient, with daily feeding leading to rapid growth and asexual reproduction through budding. Aquacultured Tubastrea is becoming more available as a result and this means survivability is much better through shipping as they can be fed properly before transporting. With proper planning and careful feeding to avoid waste, Tubastrea becomes less difficult and actually become a recommended addition to add some color to the unlit areas of your tank. Overall they are much more forgiving than Carnation Coral.  

 

     Dendronephthya does not extend their polyps without sufficient flow, once collected the colony closes and spends the next days in transit without an ability to consume any food. Upon arrival, most wild harvested Dendronephthya are shriveled and on the verge of collapse. Bringing them back can be a challenge if not impossible and requires a ready supply of phytoplankton to virtually cloud the tank several times a day. The coral may come around and begin to thrive with regular feeding, but your bioload will suffer as a result and it will put a strain on most systems to have such an abundance of phytoplankton added to the tank.

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Gorgonias

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     While not technically coral Gorgonias are an example of Sessile invertebrates that live their life firmly anchored to the reed. They consist of a long sturdy backbone-like structure wrapped in a soft, often sponge-like tissue that comprises the skin which may or may not have prominent polyps visible. Some Gorgonia, like the Purple Sea Whip and the Golden Sea Rod, are photosynthetic and are thus autotrophic and great additions to any tank with lighting and flow rates appropriate for SPS coral. Many, like the Deep Sea Gorgonia, or my personal favorite the Blueberry Gorgonian are wholly heterotrophic. Like heterotrophic coral, gorgonia need to be fed adequately to maintain good health. The polyps of a Gorgonia are much smaller than Tubastrea which makes them more challenging feed, but not impossible.

 

     Gorgonia should be fed very small prey items like rotifers or copepods. While not as readily available as Mysis shrimp, there are frozen, refrigerated and even live cultures available to the aquarist to feed to these creatures. Feeding of Gorgonias should take place daily and at several times throughout the day. Flow can be slowed or stopped during feeding however the Gorgonia may soon start to close without adequate flow so you will want to move quickly. With a baster or pipette create a cloud of the food source upstream from the Gorgonia. You may even be able to see the Gorgonia filtering the food source out of the water as it flows through. This should be done several times a feeding or until you feel a majority of the polyps have successfully captured food. Care should be taken to monitor waste levels closely in systems with the gorgonias present, as this routine style of passive feeding will lead to a significant waste build up in time.

   

Precautions

 

     When choosing the more difficult Heterotrophic coral, more consideration is required during set-up of the tank. Due to the need to feed the coral, deeper tanks that are harder to reach the bottom of may not be desirable. Instead of shallow tanks that are easy to access from any angle are preferred to allow for easier feeding. Additionally, due to the high flow rates of these corals' natural habitat, considerable larger powerheads may need to be used to properly stimulate polyp expansion. These turbulent conditions may prove too forceful for LPS coral and tear their flesh against the sharp underlying skeleton. Lastly, there is a very high probability that in feeding these corals adequately you will need to do significantly more water changes to maintain lower nutrient levels. While not as sensitive as say Acropora, Heterotrophic coral too seem sensitive to an extent to nutrient build ups.

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     It is very important to the health of your reef tank to consider these factors before adding a heterotrophic coral. The additional waste, flow or necessary space for full expansion may not be accounted for and the heterotrophic coral may not fair well; or you may adjust to account and in response, other preexisting coral may not respond well to the changes made. Ultimately, deciding before you start the tank whether or not the tank will have a heterotrophic theme will reduce the difficulty of maintaining the coral, although perhaps not by enough in some cases.

 

     When asked about heterotrophic coral, I almost exclusively discuss Tubastrea, Carnations, and Gorgonia as they so perfectly outline the unique qualities of heterotrophic coral, however, there are several related corals available such as Dendrophyllia and Nephthyigorgia but their care and success rate are so similar to Tubastrea and Dendronephthya respectively that they are easily lumped in with one or the other for basic descriptive purposes. If any of these coral appeals to you, the words patience, water changes, and possible heartbreak ought to be equally appealing or you may face disappointment.