Saltcorner
By Bob Goemans
By Bob Goemans
Not Reef Tank Suitable
Not Suitable for Fish-Only Tank
As for more desirable forms of green algae, those in the Caulerpa genus are no doubt one of the most popular. If properly controlled, they lend themselves to improving the system's environment and water quality. However, even with the more desirable species, if not controlled they can lead to throwing in the towel so to speak!
This green, terrestrial plant-like and multi-shaped macroalgae can be found readily available at most marine aquarium shops. There are about seventy different species and most are prolific growers. Root-like holdfasts grow along their rhizomes and attach themselves to substrate, rock, and even coral animals. The main purpose of these growths is to anchor the plant to a substrate surface, yet some uptake of nutrients is thought possible. However, the majority of nutrient uptake is through the fron/leaf surface.
Caulerpa are coenocytes, i.e., a multinucleate cytoplasm appearing as many interconnected segments. The proper way to break off a section of the alga is to crush the thallus (stem), not make a clean cut such as with a scissors. Clean cuts can lead to internal damage and quickly cause a section or the entire specimen to disintegrate. Beside disintegration from physical abuse, cellophaning, i.e., becoming transparent can be caused by sexual reproduction. When this occurs, the Caulerpa leaf will first become blotchy. Soon after blotchyness appears, hair-like discharge tubes called 'papillae' will form along the edges of the leaves and discharge gametes and some remaining cytoplasm.
There are some thoughts as to why Caulerpa enter the sexual cycle. Some think it is brought about by salinity changes. Some think it may simply be a biological clock. Others think it may be brought about by a lack of nutrients, e.g., carbon dioxide, nitrate, iron or that of excess organic material. No matter what the cause, when Caulerpa begins to cellophane, those leaves should be removed before disintegrating altogether. If allowed to disintegrate, the plant's nutrients will be released into the aquarium, reducing overall bulk water quality. Excellent growths of Caulerpa can usually be maintained by simply harvesting the oldest one-third of growth as necessary.
Caulerpa, as with most algae, do better under regular daylight fluorescent lamps (5500K) than under more expensive blue spectrum lamps such as 6500 or 10,000 Kelvin or above lamps. The reason for this is that algae prefer longer wavelength light, such as the red band wavelength. Higher Kelvin rated lamps have blue-green spectrum, which algae do not find as useful as red band. Caulerpa also prefer what could be termed average water conditions, i.e., where nutrients such as ammonium, nitrate, and phosphate are readily available.
In fact, I could not get macroalgae to grow in a plenum-equipped system where nitrate was constantly below 3 mg/l nitrate-nitrogen (NO3-N). Every time I tried a new specimen it would cellophane and die. As an experiment I carefully split a specimen, C. prolifera, and added half to another aquarium. This other aquarium had a sandbed directly on its bottom and its temperature and salinity were the same as the plenum-equipped aquarium. The specimen in the aquarium with the sandbed directly on its bottom grew well. The major difference between the two aquariums was that the one with sand directly on its bottom had a nitrate level of 8 mg/l. As I brought down its nitrate level, Caulerpa growth slowed. Under 3 mg/l, growth stopped and the specimen began to cellophane.
Some aquarists refer to Caulerpa as a pest because it can block light or its holdfasts annoy corals. Preventing this type stress is a simple matter of guiding new growth away from the coral animal. It is also known that Caulerpa release a toxin called Caulerpicin, which may inhibit coral growth and possibly harm some fishes. Caulerpicin and organic leachates that yellow bulk water can be removed with adequate protein skimming and/or proper use of activated carbon.
Some Caulerpa species are a favorite of herbivore fishes such as Tangs. Notice I said 'some' as I've found only two species that are usually eaten with relish (No, not that kind of relish!) and they are C. mexicana and C. prolifera.
