Green algae in the Chlorophyta Phylum are photosynthetic. This means they use chlorophyll "a" (photosynthetic greenish pigment) to capture light energy, which fuels the manufacture of food - sugar, starch, and other carbohydrates. This is what also gives these algae their green color. All plants, algae, and cyanobacteria which photosynthesize contain chlorophyll "a". This is the molecule that makes photosynthesis possible, but green algae also contain chlorophyll "b", which only occurs in this algae group and in other living plants. Because different photosynthetic pigments absorb varied ranges of light in the light spectrum, some green algae species require moderate to bright lighting while others require moderate to low lighting.
You have to remember that not all algae are well behaved, including the green macro species in this group. For whatever type of green algae you choose to cultivate, each should be cared for according to their specific requirements. Some of the most popular decorative types of macroalgae in the green algae Chlorophyta group are Caulerpa and Valonia (Bubble), and calcareous forms such as the Halimeda, Rhipocephalus and Penicillus species. This group also contains the less desirable nuisance green hair algae (Derbesia species), along with other numerous forms.
Controlling them is basically the same as with most any form of algae - remove as much as possible by hand, siphoning or filtration, reduce nutrients (DOC's - Dissolved Organic Compounds) by adding a protein skimmer, lower or remove high levels of nitrates and phosphates through proper tank maintenance, adjust the lighting levels higher or lower (depending on what type of green algae you are dealing with), use RO or DI water for make-up and top-off water in conjunction with a good quality sea salt mix (one low in nitrates, phosphates and other unwanted elements), and add the appropriate types of natural reef janitors (fish, snails, hermit crabs, crabs, etc.) that will consume the type of algae you may have. At Janet's Reef site she shares how the addition of a Sea Hare (Dolabella auricularia) helped to eliminate a bad green hair algae problem that she had been battling in her 120g reef tank for almost a year.
As we stated earlier, there are more than 7000 species of green algae. Here are some more Chlorophyta image resources to help with the identification of algae in this Phylum.
- Chlorophyta images from the Università di Catania Dipartimento di Botanica (University of Catania Botanical Department) website.
- Chlorophyta images from the Ohio University Algae Home Page.