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Today: Nov 17, 2017
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Reefkeeping 101

Pests, Parasites And Things That Go Munch In The Night, Part 2

In this month's article I will be discussing a few other creatures that can rapidly achieve plague levels in marine aquariums and what to do about them. The ones we'll look at first are the common, small starfish that hitchhike into our systems known as Asterina sp.

Public Enemy Number Two: 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. The repeated splitting in this fashion gives rise to a vast variety of body morphologies as shown in the images below.


Photos by Paul Whitby.            

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.


Photos courtesy of Dave Harms, Chuck Fiterman and Erin McGarry Brown (JokerGirl).            

In the wild, and in our systems, Harlequin shrimp will seek out stars then roll them over and devour the tube feet and ultimately the star, before hunting down the next snack. They will rapidly consume an infestation of Asterina sp., with many hobbyists reporting that there are no more visible Asterina sp. after a few months of adding Harlequins. This in itself presents an issue to the ethical hobbyist. Should we add a creature that is so demanding in its diet, a question which we each have to answer for ourselves. For my part, I have multiple tanks but only one in which Harlequins are resident - my main display. I can happily supply them with daily additions of stars from my frag tank and sump. Alternatively, there are all those other local hobbyists that are hand-pulling Asterina sp. who can keep my shrimp fed and happy. Harlequins do not require anything special other than food but do need to be cared for similar to all other shrimp in your system and as such, are not suitable for predatory tanks or reefs with larger fish which may eat the shrimp.

An alternate approach to Asterina sp. eradication is to use another, less-commonly seen Harlequin shrimp commonly referred to as a "Bumblebee shrimp" or "Striped Harlequin" (Gnathophyllum americanum). It gets this name from its radial bands of black and yellow stripes. While these shrimp are not as colorful as their cousins the Harlequins, they are not obligate feeders on the tube feet of echinoderms and thus will not require supplemental feedings of sea stars, or legs of sea stars, once they have consumed all of the Asterina sp.

Public Enemy Number Three: Red Flatworms

In last month's edition of Reefkeeping Magazine there is an article in the Invertebrate Corner that discusses flatworms in great deal. That article can be accessed here. I strongly encourage anyone who thinks that they may be experiencing a flatworm infestation to read this excellent article. I do not intend to add much to the wealth of information provided by Tom Murphy, but instead examine the known controls in more detail.

Photos courtesy of Adrian Chris.                  

As described, the common red flatworm (Convolutriloba retrogemma) can often reach plague proportions in enclosed systems. Tanks with poor nutrient export are prime targets for the rapid multiplication of these small worms. My personal experience with these creatures is limited to frag tanks for the most part, and I presume this is due to the low degree of predation as well as high nutrients due to lack of live rock based filtration. I have found manual control to work reasonably well and have often utilized cold water dips to remove them from corals. This is a very simple and easy technique to perform. In essence, I remove a gallon or so of tank water and place it in a bowl in a refrigerator for an hour. Obviously, during this time the water temperature drops, but the salinity, pH and other chemical parameters remain the same. The infested coral is then gently swirled in the water. Almost immediately, the worms will release and fall off. It is also likely at this point that you will see lots of other microfauna leave the coral, so be ready to save any tiny sea stars or pods that are affected. Once you are satisfied, after 15 seconds or so, the coral can be returned to the main tank. It is unlikely that every single worm has released, but certainly the majority will be removed. I must stress, though, to use this approach with caution. It works for me on stony corals such as Acroporas, Montiporas and Porites etc. as well as soft corals such as leathers, mushrooms and zoanthids. I have not tried it, and do not recommend trying it, with LPS or other delicate corals. This method does not eradicate red flatworms from the substrate, tank walls etc. For that I rely on wrasses. As mentioned in last month's article, the Melanurus wrasse will eat flatworms. I have also found Six-line wrasses (photo below left) to be excellent eaters of flatworms and when combined with cold water dips, a Six-line can rapidly clear an infestation. For this reason, I usually include a Six-line in my coral QT and in my frag system. Similarly, one can take the approach of using a Blue Velvet nudibranch but this, like the Harlequin shrimp, is an obligate feeder and may not be a suitable remedy to many aquarists.

Photos courtesy of Lisa Page and Greg Rothschild.                    

Tanks that have a heavy infestation of red flatworms may require chemical intervention. There are many chemicals available for doing this on the market, and I strongly suggest that a great deal of research is performed before beginning any form of chemical eradication program. Should you choose a chemical approach, it is imperative you do as much as absolutely possible to minimize the impact of toxin release. This is not a minor concern and inadequate preparation can potentially devastate a tank. Prior to treatment, I strongly suggest having on hand as much new saltwater as possible. This should be at the exact same parameters as your tank. You will require at least 100% of the tank volume (including the sump). Should anything go wrong this can be used as an almost immediate fix. Ensure that you have a good sized canister filter packed with fresh, washed, activated carbon as well as spare carbon should it be needed. Prior to beginning the chemical treatment, attempt to remove as many flatworms as possible by siphoning or any other method that works for you. Repeat this over a period of a few days. Once their numbers have been diminished, it is time to treat. Following the instructions extremely carefully, treat the tank and look for flatworm death. During this process attempt to siphon as many dead worms as possible. Once treatment has finished, perform the water changes as recommended and institute carbon cleaning of the water. Following these simple guides will protect you from the extremely toxic release of bodily chemicals as the flatworms die. It will also allow you to very rapidly change the tank water should something go wrong. Remember - this is reefkeeping, and as I am sure you are all aware, nasty things have a way of happening very fast.

The pests I have discussed above all share a common feature - until they are at plague proportions, they are more of a nuisance than a threat to our inhabitants. Aiptasia, Asterina sp. and red flatworms can be in our systems for many years with minimal impact. Keeping nutrients limited and performing routine maintenance will certainly help keep their numbers at bay. Quarantining of new rock or coral will also help in this process, as will dipping new acquisitions in one of the many proprietary coral dips prior to addition to the main tank. Aiptasia, Asterina sp. and red flatworms are all easily dealt with, both biologically or manually, and I hope the previous month's article, and this one, help you to deal with these pests should the need arise. Please remember, the approaches I detail work for most people, but not all and before beginning any eradication program, do lots of research.

In the next segment of this series I will discuss some of the truly problematic creatures we encounter, those that eat and destroy corals and those for which there really are no true remedies.

If you have any questions about this article, please visit my author forum on Reef Central.

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