Certain types of algae invasion are most definitely unwelcome. Finding green filamentous algae waving in the currents is not a good sight, particularly as it could spread rapidly. Brown, or more correctly diatom algae is another bothersome arrival, but this one is likely to disappear once the supply of silicic acid is exhausted. Another very unwelcome alga that could make an appearance in the aquarium is cyanobacteria, the horrible smear algae as it is often called. It forms a thin dark coloured blanket and creeps across surfaces.
Algae don’t have to be unwelcome though. A reef aquarium where the aquarist is reasonably diligent about calcium and alkalinity levels could develop some very decorative types. The ones I’m thinking of are encrusting mainly, appearing in colour shades of pink, sometimes brownish red, brown and various greens. They cover rocks and the back glass and give a really natural look.
In my aquarium I permit the encrusting algae to cover the back glass and the left hand viewing glass (that end is near a wall). I’ve taken a photo of the left hand end (I offer my apologies if necessary for the quality which is the best I can manage with the pocket camera owned). Anyway, it hopefully demonstrates the point.
I don’t have a lot of encrusting algae on the rocks or if I did it wouldn’t be seen. This is simply because there isn’t much rock surface visible, hardly any at all. Everything is covered with coral growth or another type of algae. There is clear evidence of pink coralline.
The other algae mentioned took me a fair amount of time to identify when it first appeared. I was a little puzzled before realizing it was in fact algae as I wondered if it was a plating coral. How could a plating coral survive and be healthy with light levels as available? I realized it wasn’t coral when I touched it as it is fairly stiff but bendable. I don’t know if there are any common names but the proper name for it is Peyssonnelia caulifera.
The colour is a reddish brown and it takes the form of mainly horizontal plates, one growing above the other. It spreads at low speed and can cover quite a lot of available space. It is an alga so is this spreading habit a problem? No, it isn’t, and this is because if a plate appears where it isn’t wanted it is very easily removed. Holding the plate between the fingers and giving a gentle tug breaks the plate free in its entirety when it can be removed from the aquarium. I have found the need to remove it from between button polyps and as said it isn’t a problem – really friendly algae.
It looks good and ‘reefy’ (I think it does anyway) between corals and adds attractiveness overall.
I’m not sure how I managed to get the stuff in my aquarium. It wasn’t knowingly imported so must have arrived on a coral rock (I didn’t use live rock at first, the inert rock used is now live though). A bit of good luck. I note that it grows the most lower down in the aquarium which is 2 ft deep and lit by a bank of fluorescents. There is some growth higher on the aquarium glass side and back but not as much. I assume the alga prefers low light levels and this is supported when some went into Peter’s aquarium. His system has metal halides and the algae didn’t like this and disappeared rapidly. I doubt it had anything to do with seawater quality as in both aquariums this is high. Hardly a scientific test but an indicator perhaps. Because the algae is a plate shape seawater currents should not be too high or the algae could be damaged or break free.
I’ve included a photo, again taken by my unprofessional hand. It doesn’t do justice to the algae but hopefully demonstrates the effect.
If Mother Nature wants to give me any more ‘freebies’ that are attractive and friendly then I’m not complaining.