RSS Common Coral Reef Pests and some ideas on how to remove them

MASA Admin

8 May 2007
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In the early days of the hobby, we paid little attention to the many small animals that came in with our corals. We had such a difficult time keeping our corals alive that little thought was paid to the potential that some of the animals arriving with the corals may have been harming them. All of this changed however, when we became successful at keeping corals over the long term, then seemingly all of a sudden myriad pests arose that could harm our charges.

By now we have all heard of blue-eyed crabs, red bugs, Acropora eating flatworms (aefw) and Montipora eating nudibranchs; all little pests that can devastate certain corals in our tanks. And while now most of us now know to look out for these pests, there are still lots more out there that can be just as damaging to our corals.

Obviously the best way to manage any of these pests is to not introduce them in the first place, and I will discuss that in my next blog, but what do you do when they are already in your tank? And just as importantly, what if you don’t even know that some of these pests are in your tank or even what they look like? Unfortunately I have encountered more “weird” pests than I ever knew existed and as a result have become adept at removing them. Also I should note that I have also introduced some fish that at first I thought would be useful in removing pests, but that eventually became pests on their own.

As I wrote earlier, corals really do not die for unknown reasons. So if the parameters of your water check out, odds are good that some coral or invertebrate predator is causing the damage. As in most families there are good members and bad members and often it is difficult to tell one from another.

Close up of the underside of an Asterina starfish on the aquarium glass. Photo Marc Levenson

Case in point are Asterina starfish. There are numerous members of this family and a large number of them like other stars are algae and detrivore feeders, that do not bother corals or other invertebrates. However there are also members that act like miniature crown of thorn starfish and like their bigger cousins can devastate patches of stony corals. The non-predatory members usually are drab colored gray or beige in color, while the predatory clan usually match the color of the corals they eat, so they will have more green or blue or even pink on their surface. All of them can reproduce wildly if food is available, and once this happens it is difficult to remove them manually.

Fortunately the Harlequin shrimp is the perfect predator to eradicate them. I have used them in several tanks and after just a couple of weeks virtually all of the stars were gone. Once the stars are gone the shrimp will die if other starfish are not available as food. So at first I mover them from tank to tank until all of the starfish had been removed. Once this was done I then moved them to a friend’s tank who was having similar problems. We now share the pair among several of our tanks as this keeps the starfish in check and it keeps the shrimp alive.

Harlequin shrimp will happily devour Asterina starfish

Just as there are good and bad Asterina starfish, there are also good and bad brittle starfish. Like the Asterina most of these are also detrivores. However, I found a variety that is very small that I had the misfortune to find out were predatory toward stony corals. These tiny brittle stars had bodies only slightly larger than the head of pin so because of their small size I did not worry about them. I only began to notice a problem with them when it seemed like every small sps frag that I introduced into my display tank where they were located started deteriorating from the bottom.

At first I could not figure out what was happening, only when I viewed these corals at night did I see that on each damaged coral frag a brittle star was wrapping around the base at night and either irritated it or was eating the tissue. I then began removing every little brittle star as I found them and I also added a group of six-lined wrasses which consumed what I had missed. Since removing these pests I have not had any problems getting my newly introduced coral frags to grow.

Unlike most reef pests, Sea Spiders ten to eat lots of different corals in our aquariums

While these first two pests are at least somewhat familiar to most of us, I have recently encountered some new pests that were completely new to me. The first of these is the sea spider, so named because it closely resembles the land-based arachnid. I had never encountered never encountered these pests until I added some colonies of Australian Acropora to my tanks. New locations for corals usually means new types of pests. These pests were not readily apparent on the colony and they tolerated the initial dip that I did before adding them to the quarantine tank. It was only after the first few nights that I noticed at least a dozen of them climbing about on all of the corals in the tank. While they did not seem to be extremely predatory to the sps corals in the tank, from reading about them I found out that they could be and at the very least they would irritate the corals. As a result I took the necessary steps to remove them over the next few nights.

The interesting thing about coral pests and predators is that they all seem to be more active at night. This was also true of a pest that I had unwittingly introduced into my tank. From time to time I add more snails to the tank to keep algae in check. After adding one batch I noticed that at least once a week one of the undersides of one of my staghorn corals would be completely stripped of tissue. I had no idea what was causing this as other than the snails I had not introduced anything new to the tank. Then one night after the lights were out and I was watching the tank, I saw what looked like a common astrea snail inching along a branch of a staghorn Acropora but in its wake was completely pure white bleached tissue. Needless to say I immediately removed it and upon reading found out that what I had encountered was a coral eating snail.

Unlike other predatory mollusks like box snails, limpets and whelks, all of which can be predatory and which I know to remove when I come across them, I added this mollusk thinking it was going to do something positive in the tank. As a result I now carefully look at anything that I add to the tank and even snails or other clean-up crew animals go into the quarantine tank before I add them to my display.

Various species of clown gobies can reduce some pests in Acropora, but they can inflict their own damage on the colonies as well

I have learned a similar lesson from some of the fish I have added. The first of these was a group of black Citrinus gobies that I added to my tank in an effort to eradicate Acropora eating flatworms. I added 6 of these fish and over the course of a couple of months they did at the very least greatly reduce the flat worm population in the tank. During this period though they grew larger and paired off into 3 pairs. This would not have been a problem except once they paired off began breeding and part of their breeding ritual is that they kill off a portion of the Acropora in which they want to breed and lay their eggs. As a result their highly amorous nature was quickly devastating my tank as much or more than happened as a result of the flatworms. So once this was discovered they had to be removed.

A similar problem arose when I added an aiptasia eating filefish to eat the aiptasia outbreak that occurred in my tank. Like the gobies this fish did a wonderful job at first, unfortunately like the gobies once the main job was done it found a second job of consuming the bubble tip anemones that were in the tank. Apparently tilefish do not differentiate between desirable and non-desirable anemones, so another pest that I deliberately introduced into my tank had to be removed.

As I said most of the pests in my tank seem to be more active in the tank at night, so as a result I have developed ways to remove them when they are active. Long after the lights are off I sit in front of the tank with a red LED flashlight as well as a bright white LED flashlight. I also have several pair of long handled tweezers as well as either a ½” or 1” diameter hose that is at least 8’ in length. If I know a pest is present I start a siphon in the hose and run it from the display into the sump and once the siphon is started I stand on it to stop the flow while I look for pests using the red light to illuminate them.

Bristeltail filefish are effective at eating pest anemones, and desirable anemones as well

The red LED flashlight is great in that it provides enough illumination for me to see a pest in action, but because it emits only red light the animal does not see the light. This then allows the animal to be removed rather easily as they will stay still under this light, but would not do so under white light. For slow moving pests like the snail of other mollusks I simply pluck them out with the tweezers. But for fast moving pests like the gobies or even the brittle stars I put the hose near them while using then red light to see them then when the hose is close enough I lift my foot, start the siphon and suck them out of the tank. Using this method I was able to remove the gobies in 4 nights. Using the red light and searching the tank late at night I also removed over 40 fire worms that were eating corals as well as several pair of blue eyed crabs, hairy crabs and a cowry that had gone rogue and was eating soft corals.

I realize that there are many more coral pests out there than I mentioned here, so I just wanted to acknowledge that as we keep getting better at this and get corals from more places that we are likely to encounter more and more pests. Fortunately knowing this and with a strategy for preventing their introduction or a plan to remove them if they are present the battle can be won. But like everything in the hobby it takes time and patience.
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