There are numerous types and colors of algae that are referred to as hair algae. Probably the two of most interest are Derbesia and Bryopsis. These two green filamentous hair-like growths are considered a major pest. Both are presently being considered cyanobacteria that contain chlorophyll. The first and most difficult of the two to overcome is a true hair-like growth called Derbesia. Its long, soft, and hair-like strands can rapidly cover wide areas. Not only can it become somewhat independent of bulk water nutrients once established, trapped detritus/debris can add further nutrients to the bulk water.
The other hair-like alga is Bryopsis plumosa. Its feather-like and upright growing structure occurs as a single stem-like plant with multiple long plume-like tufts. It also can become somewhat independent of nutrients from the surrounding bulk water once the plant structure becomes recognizable.
Both Derbesia and Bryopsis plumosa have two life cycles, i.e., as a small bubble-like growth and that of an easily recognizable plant-like structure. Derbesia has tiny spore packages called "sporangia" that form along its hair-like strands. When these packages mature, they burst open and release spores that settle and grow into "gametophytes" which look like small green bubbles. When these bubbles mature, they release male or female germ cells that eventually unite and form a "zygote," which is the base unit for the growth of a new structure of hair algae. Though some aquarists say algae does not grow on surfaces covered with coralline, that is not true. Quite frequently the early stage bubbles of Derbesia can be found attached to surfaces covered with coralline in the genera Sporolithon and Hydrolithon.
Other occasionally seen algae falling into this grouping include Boodlea, which forms fine, short light green brittle growths that fragment easily. Its sometimes referred as the "Crunchy Hair Grass." Another is Chaetomorpha, which has more course wire-like strands and can be found in a variety of forms from simple hair like growths to woven masses. However, for refugia and/or alga turf filters, this is an excellent fast growing alga providing for nutrient export. A similar looking hair algae is Enteromorpha, which is light green and tends to grow in tufts or clusters, and sometimes are found attached to other plants and organisms. There's also a red hair alga in the genus Polysiphonia that can be quite troublesome.
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Suitable for Reef Aquariums
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Suitable for Fish-Only Aquariums
NOT Suitable for Fish-Only Aquariums
Avoid this nuisance species!