QUOTE (lakshwadeep @ Mar 2 2010, 05:01 PM)
Bleaching is when an anemone (or coral) expels its symbiotic zooxanthellae algae, usually under stress. Stress includes poor water quality. Bleaching can also occur from strong lighting, but that is rarely the case for anemones in holding tanks. Because of this, bleached anemones are vulnerable to dying if not fed enough and kept under very good water quality. Even then, some anemones will be too far gone to save.
This article has great information regarding the subject if anyone hasn't seen it:
http://www.coralscience.org/articles/PDF/H...rals%20feed.pdfQUOTE
Sometimes, algae produce too much oxygen; this is harmful for all living cells, as a part
of these molecules is converted into radicals. These are reactive molecules which contain
extra electron pairs, which is why they love to interact with other substances. This
causes DNA and cellular damage in the cell. Fortunately, corals have found a way to deal
with this nuisance, by producing molecules called anti-oxidants. These bodyguards
absorb dangerous radicals, thereby protecting the cells. They can also expel
zooxanthellae which produce too much of these molecules. This eviction notice, which
leads to coral bleaching, has two main causes: First, high levels of photosynthesis are a
common culprit. This sometimes happens in the aquarium when we switch from T5 to
metal halide lighting too quickly. This means it is important to allow corals to adapt
slowly to new and stronger lighting.
Second, many coral species bleach at water temperatures of 30°C (86°F) or higher; this
is because zooxanthellae are damaged at such high temperatures. The thylakoid
membranes inside the chloroplasts simply fall apart, allowing many oxygen radicals to
flood the coral tissue. This again triggers algae expulsion. Some zooxanthellae, however,
are resistant to temperatures of up to 32°C (90°F), and this explains why some corals do
not bleach during a hot summer (see archive).
After bleaching, corals have to reacquire their algae population in time, before they
starve to death. Fortunately, this process is often successful. This also occurs in the
aquarium, and this is possibly due to the reuptake of free-living zooxanthellae through
the mouth and gastrovascular cavity. Many coral larvae also do this before they
metamorphose into primary polyps (see archive). In addition, partially bleached corals
simply regrow their remaining zooxanthellae.
