Asterina sp. Starfish
There is a pretty good chance that, like Aiptasia, we will all encounter Asterina sp. starfish at some time within our tanks. At first, we may consider these small creatures to be interesting new arrivals that have clearly hitchhiked in from somewhere - most likely a recent coral or live rock purchase. Maybe we will see one, or maybe two, and be more bemused about where they came from than what they are. Then, in the space of a few months they appear to be everywhere, be it on the glass, the rocks, corals - in fact any accessible spot. It is usually during this population explosion that the curious aquarist begins to wonder if these creatures are creating other issues besides detracting from the look of their tank. Around this time it is likely that the hobbyist will look for information and suddenly be bombarded by wildly varying opinions on these creatures ranging from benign addition to devastating coral killer with the result that a program of eradication rapidly ensues.
Debates over the nature of Asterina sp. stars have been waged for as long as these creatures have been observed in marine tanks. The sheer number that a tank can support is startling and can often fool the new aquarist into believing they simply must be eating their prized coral specimens. On the other hand, there are seasoned aquarists who have lived with Asterina sp. for decades with no noticeable problems. These contradictions can be very confusing to the novice aquarist. The reasoning behind these wildly varying opinions is that Asterinas sp. can indeed be both - either a benign addition or a coral killer, and it is currently not possible to definitively test or identify which type is in any one tank. At this point it should be said that there are many different species of Asterina sp. and of them all, only a few have ever been recorded to eat coral such as Acropora, zoanthids and other soft corals. The vast majority are opportunistic scavengers and/or herbivores that eat coralline or other types of algae. It has been estimated that of all the Asterina sp. varieties, only around 5% are coral eating species, which is good news for aquarists since they are so common in our systems. However, there are more than enough documented cases of corals being eaten by Asterina sp. to convince even the hardened skeptic that not all Asterina sp. are alike, and that some are, indeed, carnivorous. The good news is that it is unlikely that benign Asterina sp. suddenly become crazed coral killers, so chances are, if you have not experienced coral loss, you likely will not - at least not until another potentially carnivorous strain or species of Asterina sp. arrives in your tank. The bad news is that coral eaters are out there and with the population density that can be rapidly attained, they can become a serious pest in a short order. I have kept corals for over 20 years and have had Asterina sp. in virtually all of my tanks, but have yet to observe coral damage that I can absolutely pin on an Asterinas. I have, however, seen other tanks where Asterina sp. have decimated corals. Hopefully, your experience will be similar to mine, and you will find Asterina sp. to be simply a nuisance. Like many things in this hobby, though, erring on the side of caution is probably the prudent option. Hopefully, this article will provide some insight into Asterina sp. stars and what approaches you can take to limit them should you so desire.
Asterina sp. are members of the echinoderms and are small sea stars that commonly have very irregular and asymmetric bodies measuring anything from a few millimeters to just over a centimeter in size. They are generally a whitish grey color, but some may be brown or even pale green. Some of them will resemble normal small stars while others will have a varying number of legs, all of which may have varying length. In fact, some do not appear to have any legs at all but just resemble a small greyish blob surrounded by tube feet. The reason for this irregularity of body is due to the fact that Asterina sp. can reproduce asexually by splitting in two across the center. Obviously, each daughter star would have a full set of legs on one side, and none on the other - at least until they more grow.
As I stated above, most Asterina sp. are benign and are actually beneficial to a marine system in that they are opportunistic feeders, grazing on algae-encrusted hard surfaces. In the past they were considered highly desirable and a great asset to a tank, helping to remove detritus and cleaning rocks. With the advent of a few reports of coral losses and Asterina sp. showing predatory tendencies, many people have adopted the approach of eradication. Unlike Aiptasia eradication, however, there is no chemical control of Asterina sp. populations. Instead, we have only biological controls. This can take two main forms, manual removal of them or eradication by the introduction of one or more Harlequin shrimps. Of the two, I would very strongly suggest Harlequins because manual removal constitutes a never ending task. Plus, Harlequin shrimps are pretty cool creatures in their own right.
Should you try to perform manual removal, I would suggest using forceps to remove them from rocks. However, they can be simply scraped from the glass surfaces and collected in a small net. There is no real technique to this and requires only time and diligence. Having collected Asterina sp. in this fashion, you may want to see if anyone in your local vicinity requires Asterina sp. to feed the Harlequin shrimp they may have in their tanks. This may seem odd, but once you realize how rapidly Harlequins can consume these little stars, you will most likely come to the conclusion that a Harlequin, or two, are the approach you should also take.
As I have eluded to several times above, probably the best method of eradicating Asterina sp. is by adding Harlequin shrimp(s) to the tank. Harlequin shrimp (Hymenocera elegans) belong to the family Gnathophyllidae and are small, white shrimp with camouflage markings that vary from brown through grey to a purple blue. They are unusual shaped in that they are small and squat and have large adapted front claws that resemble paddles. Harlequins are obligate sea star eaters, which means they will ONLY eat starfish, and nothing else. This is why people picking Asterina sp. by hand are often asked for donations from those with Harlequins.
