Tentacles on my anemone are disappearing. What’s going on?
If all the tentacles on your anemone are shrinking, it is normally a sign of starvation. If
only some of the tentacles are missing, shrinking, or deflated, it is a sign of physical
damage.
Anemones will grow quickly if they are in a healthy environment and have bright lighting
and a secondary food source. However if the lighting is dim and they don’t have a lot of
secondary food, the anemone will start to wither away as it consumes its own body
tissues to stay alive. One of the most striking signs of this condition is when the tentacles
become shorter and shorter – appearing like nubs or bumps on the oral disk. Anemones
can recover from this condition, but only if they are placed in a healthy environment with
good water and proper lighting. Secondary targeted feeding can help, but it is normally a
short term solution if other factors are not in line.
Anemones can be physically damaged (and lose tentacles or have shrunken tentacles) by
many sources. Frequently it can be predation by another fish – either a clown or small
angel or other reef fish. Anemones can also be stung by large LPS colonies like
frogspawn or bubble corals. Finally, anemones can be preyed upon by large worms
(especially if the damage only occurs at night). There are other (less common) predators
as well. The sign of predation is always localized damage on the anemone.
http://www.carlosreef.com/AnemoneFAQ.pdf