The wild reefs are home to some pretty weird creatures and some of these creatures can be really attractive. The nudibranchs fall into this category, to me anyway.
On the wild reef many creatures have a niche for the supply of food. Some fish will just cruise along devouring their type of food, the usual example given are surgeons which often move in shoals eating algae. There’s a fish that farms algae and will aggressively defend the area from interlopers such as surgeons, though faced with a large shoal it has little chance. Some life forms are predators, others omnivorous. Whatever food is available, there’s something there to eat it, which is Nature’s balance.
Nudibranchs are the same; they have a food niche too. The food supply for all nudibranchs is not the same, most will predate on a particular type. Unfortunately for the reef aquarist, this food is often a type of coral.
Many aquarists check corals and coral rocks when they are purchased to try to ensure, as far as possible, that there aren’t any unwanted organisms. What are usually in mind are those weeds of the reef aquarium, aiptasia, and similar growths. It is possible that a nudibranch could be found.
I recall that many years ago I obtained a soft coral from my LFS, complete with rock. A general check was made of the coral and rock but nothing was seen to make me suspicious. A while later, maybe a couple of days to a week, I noticed the coral seemed to be unhappy and reducing in size. What made me examine it again along with its rock I don’t know but this is what I did. Underneath the rock in a crevice were two yellow nudibranchs. I removed them from the aquarium and placed them into a bowl which was floated in the aquarium. Attempts to identify the type of nudibranch failed. I took them to the LFS but they died.
The two nudibranchs I found will have been predators of that particular coral, which is why they were imported with it. If they had been left the coral would quite probably have been completely eaten, or been so badly mauled that it would have died. At that point it would have been death for the nudibranchs as there wasn’t any other coral of the type is the aquarium. That is why they died at the LFS, there wasn’t any food for them.
It is understandable therefore why nudibranchs are not a common feature of reef aquariums. There are very few aquarists who would be prepared to feed corals to them, no matter how beautiful the creature might be.
Many of these creatures have colouration which reasonably matches their prey, a defence against being predated upon themselves and making them more difficult to spot. Others have bright colours to warn that they are distasteful or dangerous to eat.
It isn’t just corals that could be the prey item for nudibranchs; some eat worms, fish eggs, mollusks etc. It is clear that all of them present a very difficult maintenance problem for the aquarist.
Nudibranchs (pronounced ‘nude – i – branks’ by the way) are really fascinating and strange creatures possessing different beautiful colouration. It is a great pity that they are not suitable for the captive reef. If they were, I for one would keep a couple.
The link provides just a few pictures of these creatures, there are many more types. Click on individual pictures to enlarge them.