Hermit Crabs in a Reef Tank
Ron, in the past you have mentioned that hermits were not good for a reef. Can you elaborate on that? A lot of people keep hermits, I am wondering what they do that is good and what they do that is bad.
The masses of hermits that folks seem to be having in their tanks create a decidedly abnormal situation, as such herds are simply not found on most reefs. Their crawling over animals such as corals and sponges is abrasive and destructive. They also remove food from sessile animals such as corals. Additionally, hermit crabs are at least partially predatory and the bigger ones are particularly a problem in this regard. Some of them are significant predators on small snails, other small crustaceans, and each other. When folks see hermits gleaning materials from the rock surfaces, they are seeing the hermits pick off small animals as well as small plants. This results in an abnormal surface that has only the animals and plants that are hermit crab resistant living on it. Additionally, at least some of them appear to be predatory on some of the worms living in the sand, and I think this is decidedly a problem.
Upon the removal of hermits from my reef (and their replacement on the sand by Nassarius snails as scavengers) I have noticed a significant new growth of smaller polyped animals, as well as small feather duster and other tube worms. I have not noticed an increase in algae. Basically, I feel like the hermits are an unnecessary complication in high numbers. Some species I think don't belong in an aquarium under any circumstances, but others like the small blue legs are probably benign if there are only one or two in a system.