The Pulse Coral

The pulse coral belongs to the soft corals and is well known. It is often seen in local fish shops and though often at a higher price than many other soft corals, is not out of the reach of most aquarists.

These corals are attractive in general, but the main attraction is the pulsing of the polyps, they rhythmically open and close. There has been considerable argument over why this should be, and the most obvious answer held sway for quite a long time. This answer was that by pulsing the coral drew suspended food particles to it so that they could be captured. Watching the coral’s action this seems reasonable. However, the latest thinking that I am aware of is that the pulsing is to obtain more oxygen, in other words a breathing movement, more seawater is passed across the polyps thus more oxygen becomes available. Some aquarists automatically dismiss this as it is compared to the similarity of human breathing. Several authorities support the ‘breathing’ reason. I am not able to state the scientifically proven correct answer. Perhaps there will be scientific enquiry into the coral and facts will emerge. If they already have I’d be pleased to know.

Anyway, the attractive coral is upgraded to fascinating by the pulsing of the polyps. Sometimes in an aquarium the polyps cease to pulse, or only pulse weakly. Again, at least to me a definitive answer as to why this should be is not known. There has been argument, some saying that in an aquarium iodine is likely to be lacking and this causes it. However, some have measured for iodine and found it present at a correct level yet there isn’t any pulsing. Others have suggested that the aquarium may have saturation levels of oxygen and there isn’t a need for pulsing. The latter one could have some merit if the coral’s reason for pulsing is related to oxygen. (The respiration reason for pulsing is cited in some respected books.) Another reason suggested is that there is excessive nitrate in the seawater. If the polyps reduce their pulsing action nitrate is easily checked for, but unfortunately there doesn’t seem to have been any feedback from aquarists on this point (to my knowledge).  Again perhaps science will come to our aid one day. The good thing is that even if the pulsing does reduce or cease, the coral does not seem to decline and remains attractive.

Pulse coral is the major common name, Xenia elongata or Xenia umbellata the proper ones (two separate types). There are other pulsing corals. They are suitable of course for a reef aquarium. The coral has a thick ‘trunk’ which leads to many ‘branches’, which in turn split off and lead to many polyps. The coral attaches to rock. It is important that the coral receives sufficient light as the flesh contains zooxanthellae which supply the majority of the coral’s food requirements. Ensure the light reaching the coral is direct and bright. Seawater movement should be moderate. Excessive seawater movement will have a detrimental effect.

The pulse corals are not difficult to keep and do well in an aquarium, provided of course that seawater quality is high and lighting is adequate. Placement seems to be one key to success (as with many other types), this could be a little problematic as placing the coral higher up the reef should provide sufficient light but perhaps too much seawater movement. When placed, watch the coral, does it expand properly and does the expanded coral look comfortable, that is not banging about in the current? It is easy to see when things are fine.

Having a pulse coral in the aquarium certainly adds to interest to state the least. If the pulsing action reduces or ceases, first be sure there isn’t excessive seawater movement. Then check for nitrate, if the level has increased reduce it by increasing the amount of routine seawater changes, at least temporarily. Investigate the reason for the nitrate increase and correct it. (The guideline for nitrate in a reef aquarium is 10ppm or less.) As a final check, all else having proved not to be the reason, check the seawater oxygen level, perhaps the seawater is carrying the maximum? Overall though, this coral should give little trouble.

The link below will give further information and photographs, just scroll down the page, lower down is a picture of a coral in action.

http://reefkeeping.com/issues/2004-02/ac/feature/index.php

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Tags: aquarium-livestock, coral, Coral Reef, marine reef, pulse coral, reef-tank