Dear Charles,
I don't know of any aeolid whichs feeds on Acropora but I guess its certainly a likely candidate for a hungry aeolid. I have summarised most of what we know about coral feeding nudibranchs on a separate page. One way coral-feeding aeolids differ from other aeolids, which usually feed on hydroids and sea anemones, is that they have lost the cnidosac at the tip of the cerata. Instead the tips of their cerata are swollen with large gland cells, which I presume produce defensive secretions [see Coral-feeding - defensive adaptations ].

If you look at your animal, the tips of the cerata are a bit swollen and do seem to have glands at the tip, so it is possible that you have an aeolid feeding on Acropora.  I am afraid the only way to be sure would be to leave the aeolid where it is and see if it grows and the Acropora continues to decline. I would suspect if it is small and you have noticed damage to the coral then there may be a group of these aeolids present. Probably not what you wish to hear, but very interesting to me.

Best wishes,
Bill Rudman

Dear Joanne,
There is a lot of information on coral-feeding nudibranchs in the Forum. As a general rule, if you are looking for information on the Forum use the SEARCH button. If you type coral, for example, you will get a list of relevant pages to go to. Your best bet would be to got to the Coral Feeding Index Page.

Are these animals parasites, commensals etc etc? It is all a question of definition. Is a large mammalian herbivore which only eats certain plants a parasite, a symbiont or commensal - or is it just a grazing herbivore? I remember Russell-Hunter in one of his books questioning why an enormous lion, feeding on prey much smaller than itself was considered 'noble and brave' while a flea or tick, living a perilous life feeding on an animal much larger than itself, was despised by us, its very name being used as a term of abuse.

I think it is more important to understand an animal's relationship to the other organisms they are associated with, rather than find them a label. Most of the nudibranch coral-feeders have a very close obligate relationship with a particular species of coral, and often they have modified their shape and colour to enable them to hide on their coral food, which becomes their home as well as their food. At the same time some of these nudibranchs have evolved a close relationship with the coral's symbiotic zooxanthellae, removing them from the coral and keeping them alive in their own tissues.

Read the information in the Forum on these fascinating animals and see how they fit the definitions you have for commensals, parasites etc.
Best wishes,
Bill Rudman

Dear Melissa,
Some nudibranch sea slugs eat corals. Have a look at the Coral Feeding Page, where you will find an index of topics about coral-feeding nudibranchs.
Best wishes,
Bill Rudman.