Asterina sea stars have been accused, unfairly at times, for preying on coral tissue. While some individuals appear to eat some desirable reef invertebrates, the problem may be a simple matter of an opportunistic predator adapting to a change in the available, preferred foods (worms, algae).
Returning to our example of the common, small Asterina species found in some reef tanks, these sea stars in recent years have suffered, unfairly I might add, the reputation of being risky or just plain un-safe in the reef. This is interesting because for many years prior to that, they were not only regarded as harmless, but beneficial! What happened? Did they all change their voter registrations overnight? No, the answer really is quite simple. It also explains why some other "controversial" reef invertebrates have contradictory reputations like Mithrax/Mithraculus crabs. Many such creatures are opportunistic feeders. While they favor one type of prey that is convenient or popular to us, like sand bed worms, brown diatoms or bubble algae, they will adapt to eating other food items following the reduction or absence of a preferred food item. Thus, the reef keeper with a persistent growth of microalgae in a garden reef display will likely have less trouble with misbehaving omnivores than another aquarist with an aggressively skimmed and scrubbed tank that supports little growth of the matter. In a phrase, the hungrier that a so-called "reef-safe" creature gets, the less "reef-safe" that creature becomes. In the case of Asterina, many years ago during the bare-bottomed, nutrient poor Berlin style era of reef keeping, reef husbandry with early protein skimmers and limited nutrient export processes was not as efficient as it is today; diatoms and other nutritious growths grew quickly in our tanks. And Asterina were not considered un-safe by hobbyists.
