Most aquarists realize it's difficult to find algae on the reef in the wild. Yet, there's always some calcareous and turf algae because they are actually important building components of any natural reef system. But with the reef's surrounding water nutrient poor and herbivores keeping what there is of algae well mowed, little or none is readily visible. Nevertheless, it's another story in shallow inland waterways and bays where nutrients have a tendency to accumulate. There, algae in various forms and amounts can easily be seen and it's these types of algae that present the most problems for many aquarists.
There are many forms of green algae, with many species serving useful purposes, e.g., could be a food source; decorative purpose; inhabitant shelter; or a means to export nutrients such as those used in refugia or alga turf filters.
One of the most beneficial reasons for maintaining some species of algae in aquarium is that their photosynthesis process uses carbon dioxide and in turn provides oxygen for the aquarium animals. This also helps raise system pH and increase system carbonate buffer capacity (alkalinity). They also help to remove unwanted compounds such as ammonium; nitrate and some heavy metals from the bulk water, thereby acting like a form of chemical filtration. Keep in mind the nitrate removed is broken down by internal enzymes, similar to reverse denitrification, until the ammonium needed for growth is attained. Removing or pruning back growth serves as a way to export the absorbed unwanted nutrients.
It would be far beyond the scope of this Algae Library to name all the species that can show up in aquaria or in the trade. However, I'll discuss the more commonly seen species in relation to what is the most beneficial and those that have the potential to create problems in the aquarium and/or give aquarists gray hair!
As for more desirable forms of green algae, those in the Caulerpa genus are no doubt one of the most popular forms. 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 than under more expensive blue spectrum lamps such as 6500 or 10,000 Kelvin 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.
Nevertheless, there are those forms of algae that are problematic, such as hair algae (long hair-like or plume-like growths); slime algae; turf algae; bubble algae; and, a very specific green microalgae.
I'll divide the Green Algae Library into areas, such as 'Macroalgae, which will contain different Caulerpa species, Hair Algae, Bubble Algae, Turf Algae, Calcareous Algae, and Microalgae. Hope you find it helpful.
As noted in the other sections/groupings in this website, there's room for additions and no doubt corrections. I've laid the groundwork, so please let's not criticize, simply pitch in and help! And since this is a visual gathering of this aspect of aquarium keeping, there's little or no related husbandry text explaining the conditions these species require or prefer. However, for that I highly recommend reading my Marine Algae Control Secrets booklet, Julian Sprung's Algae, A Problem Solving Guide, Vincent Hargreaves The Complete Book Of The Marine Aquarium, or Anthony Calfo & Bob Fenner Reef Invertebrates, An Essential Guide to Selection, Care and Compatibility. These books will greatly help you understand the conditions that bring about or sustain these growths and further ways to control or eradicate them.
Please click on the Algae (Green) group you are interested in viewing.