Organisms belonging to the division Rhodophycota of the Kingdom Protista.
Most of the over 4000 known species of red algae
are marine. They range in complexity from simple unicellular organisms to
unbranched and branched filaments to complex multiaxial uprights and crusts.
Their pigments include chlorophyll
a and the phycobiliproteins, red phycoerythrin (often the dominant pigment)
and blue phycocyanin, as well as carotenes,
lutein, zeaxanthin. Phycoerythin reflects red light and absorbs blue light.
Because blue light penetrates water to a greater depth than light of longer
wavelengths, these pigments allow red algae to photosynthesize (see photosynthesis)
and live at somewhat greater depths than most other algae. Some rhodophytes
have very little phycoerythrin, and may appear green or bluish from the
chlorophyll and other pigments present in them. Most red algae have a complex
life history with three phases: tetrasporophyte, gametophyte, and carposporophyte.
| Red algae. Photo: US Dept. Natural
Resources and Parks
In Asia, rhodophytes are important sources of food, such as nori. The high
vitamin and protein content of this food makes it attractive, as does the
relative simplicity of cultivation, which began in Japan more than 300 years
ago. Some rhodophytes are also important in the formation of tropical reefs,
an activity with which they have been involved for millions of years; in
some Pacific atolls, red algae have contributed
far more to reef structure than other organisms, even more than corals.
These reef-building rhodophytes are called coralline algae, because they
secrete a hard shell of carbonate around themselves, in much the same way
that corals do.
Sources: NOAA and the University of California, Berkeley