Enough Light? Must Be

Aquarium Lighting

Watching a marine aquarium is a great pleasure and probably one of the major reasons why so many keep them. With a reef system sometimes a new arrival is seen to appear, or a species of coral that is already present appears somewhere else.

On a few occasions I’ve noticed arrivals that must have come in with coral rock, such as a very dark and tiny crab that was very timid and only appeared at ‘dusk’. Its presence was shown by an exploratory claw appearing out of a crevice. The crab hasn’t been seen for a long time and no doubt has gone.

Corals too can appear when new live or coral rock is introduced. In this case the coral type is already present in the aquarium with a fairly large colony, and the new appearance is in a completely separate part of the aquarium.

As far as I can tell, the main colony is a Rhodactis species (the purchase was made years ago and the dealer didn’t have a clue). Rhodactis are also commonly known as hairy mushrooms and mushroom anemones. I think it could possibly be Rhodactis indosinensis – but is this correct as most grow larger than my specimens? Maybe they are Discosoma species. The colony is receiving plenty of light as it is half way up the reef (about half way up the aquarium depth). The new one, however, is not; it is right down at the bottom. The aquarium is 24″ deep (21.5″ from lights to coral). Further, this new growth is at the end of the aquarium and is partly shadowed by another coral.

Is my lighting system powerful? No is the answer, it’s a fluorescent array of five tubes, three marine whites and two marine blues (actinic). They’re not even T5’s, they’re T8’s. The reef is furnished with soft corals and they are perfectly happy but I had to wonder at the growth of this new one. The blues will penetrate well but even so….

The original colony is in an ideal spot apart from seawater flow which is a bit too vigorous, they prefer weak flow. However, I’ve left things as they are as the mushrooms are clearly healthy and open well, though not to as large an extent as with lower seawater flow.

The new one is the reverse; it’s in an area of slow flow. However, as said, I wondered about the light. It has been slowly growing for about 8 months now and has reached a size of 3″ across, which, because of the slow seawater flow, is full expansion. However, though I believed the slow growth must be because of light, or at least the lack of it, it seems this could be wrong. Looking at one of the references available to me * it seems that though light is no doubt an influencing factor it isn’t that important, as strong lighting is not required by Rhodactis species though they will tolerate it. Discosoma species prefer in many cases reduced light.

How did the new growth appear? It is possible it’s by natural detachment, but in this case is more likely to be my error. From time to time I have to get out the trusty and sharp scissors and reduce the colony to prevent interference with other species. Part of this is catching the detached parts. These corals are easy to ‘frag’ so if a small part escaped my attention and lodged it is more than likely to grow.

So there we are – what started as a general belief followed up by some simple research has turned my notion upside down. Goes to show how important basic research is. As far as identifying the species, I’d need a marine biologist and I bet there’d be uncertainty even then.

(*Reference: Aquarium Corals. Eric H. Borneman)