Unique to the red algae and the cyanobacteria, members of this division have a clear red or purplish color supplied by pigments called phycobilins. The chloroplasts (cells which produce food from sunlight) of red algae are believed to be derived from cyanobacteria that formed an ancient symbiotic relationship with the algae.
Nearly all of the approximately 4,000 known species of red algae are marine and are most commonly found in warm-temperate and tropical climates, and can be found at greater depths than any other photosynthetic organisms. The red algae are multicellular and are characterized by a great deal of branching. The cell wall of red algae has a firm inner layer containing cellulose and a mucilaginous or gelatinous outer layer. Cells may have one or more nuclei, depending on the species. Cell division is by mitosis (process of nuclear division in a living cell by which the chromosomes are exactly replicated).
Rhodophyta (red algae) have been found at depths of up to 879 ft (268 m), where the wavelength of light available for photosynthesis is very different from that in shallow water. However, a vast majority of the red algae used (as fish food) in the aquarium trade is found in shallow waters inside the reef.
Species of red algae which are used in the aquarium trade as food for herbivores include:
- Botryocladia sp.
- Gracilaria coronopifolia
- Gracilaria parvispora