04
Jul

Majano anemone | Aquarium friend or foe?

If you’re new to the marine aquarium hobby, it can be a surprise to suddenly find a colorful anemone in your tank. Is it good news? Or should it be removed because it’s bad for your system? Today in FantaSEA Aquariums’ Friend or Foe section: the majano anemone.

Keep reading for everything you need to know about the majano anemone, whether it’s good or bad and how to remove it from your aquarium.

What is a majano anemone?

You may have heard of the concept of hitchhikers, which are creatures that can end up in an aquarium by “hitching a ride” on live rock from your local aquarium store. Some of these are ugly but beneficial, like the spaghetti worm. Others, like those listed on our dreaded list of the most unwelcome aquarium hitchhikers, we’d rather not encounter in our tanks.

One of the creatures that can pop up in your aquarium seemingly out of nowhere is the majano anemone (whose scientific name, confusingly, is Anemonia manjano, with an added N). The species is widespread in the Indo-Pacific and, unsurprisingly for such a hardy invertebrate, is also invasive in some areas.

Majano anemones can be recognized from their small size (no more than an inch or two), with a tannish-brown foot and light brown tentacles that end in a rounded tip. This tip is often neon green or pink in color, which actually makes this species pretty nice to look at. The color comes from the anemone’s zooxanthellae, microscopic algae that allow it to photosynthesize.

Majano anemone: Aquarium friend or foe?

So which category does the majano anemone fall in? Is this an aquarium friend or foe? Well, unfortunately, it’s a total foe. Despite its size, it can wreak havoc in reef tanks. Heck, it even does so in the wild, as shown by 2015 and 2018 studies in Vietnamese and Philippine waters.

Finding these anemones in your tank can seem like a lucky coincidence at first. Their colorful tentacles waving in the flow are pretty decorative, after all, and it’s interesting to see how they can move around in search of light and floating particles to consume.

Not all anemones are easy to grow, with some actually being quite challenging. The problem is that this one is. It’s very easy to grow. It’s also very easy to multiply, and in fact does so by itself without any intervention from your side. And before you know it… your whole aquarium is nothing but majano.

Did you know? Majanos are not the only unwelcome anemones that can pop up in the aquarium. There is also Aiptasia, which is similar but can be told apart from its longer, pointed tentacles. Majano anemone tentacles are shorter and end in a stubby tip.

Majano anemone | Aquarium friend or foe?

Why are they bad?

Majano anemones by themselves are too small to do much damage to anything. Their tentacles aren’t nearly large enough to catch fish and most corals have their own defense mechanisms.

The problem is that the concentration of stinging cells (better known as nematocysts) in the water can become too high for your protein skimmer to deal with if you’re dealing with a full-blown plague. This causes the health of corals and other invertebrates in the tank to decline. Anemones all around them can sting corals to a point where they’re just not able to thrive or even survive.

If you think you can just keep the anemones under control and enjoy their colors without things getting out of hand, think again. Although there are some aquarists out there who don’t keep corals and therefore have no issues with majanos, it’s almost impossible for things not to go south at some point.

The main problem is that, when stressed, anemones like this one release a cloud of spores. There can be hundreds, and each has the capability of growing into a new anemone. This means that every time you poke at a majano while trying to remove it, you run the risk of multiplying it. Even when not stressed, they’re constantly shedding tiny copies of themselves.

Majano anemone removal

OK, by now, we’ve probably drilled into your head why these anemones are not a welcome sight in your reef aquarium. But what can you do if they explode with spores every time you bother them? Getting rid of an infestation can be extremely tedious, but it can be done.

You can remove a majano anemone by hand, though it’s important to keep in mind it takes some practice to be able to do so without leaving pieces that can then regrow. It only takes a tiny bit of anemone to make a brand new one!

Let’s have a look at some more sophisticated weapons you can consider adding to your anti-majano arsenal. Remember to always monitor your nitrate levels and not overdo it!

Tools

The most useful tool we’ve found for killing majano anemones is a commercial product called the Majano Wand. It’s every bit as magical as it sounds.

Although you have to practice a little to make sure you don’t accidentally make the anemone release its spores, this is a great majano killing tool. It’s a bit costly, but it disintegrates the invaders from the inside, which can be immensely satisfying if you’ve been struggling with an infestation for a while!

Chemicals

Yep, the classic method of using chemicals to get rid of pests can also work for a majano infestation. Regular ol’ vinegar unfortunately doesn’t tend to cut it, though, meaning you’ll likely end up working with calcium hydroxide. This can alter your tank’s water values (acidity and alkalinity) if you’re not careful, and it’s also dangerous to get on your bare skin. Proceed with caution!

Your plan of action for using chemicals will usually look a little like this:

  • Pick your poison: calcium hydroxide (Kalkwasser, also known as pickling lime), Aiptasia-X, Joe’s Juice.
  • Follow the instructions for mixing the solution.
  • Turn off filters, pumps and powerheads.
  • Use a syringe or an applicator like Julian’s Thing to inject the solution right at the anemone’s oral disk to make sure it ingests it.
  • Sit back and marvel as the invader shrivels WITHOUT releasing its spores.
  • Turn equipment back on and monitor the tank to make sure the chemicals don’t touch any of your corals, as they will die if this happens.
  • Monitor nitrate levels, which can spike if there are too many dead things in the tank.

Fish

Unfortunately, many of the fish and invertebrate species that work well for clearing other pests from the aquarium really don’t seem that interested in majano anemones. There is one solution, though: the bristletail filefish (Acreichthys tomentosus). We’ve personally had great experiences with this small but efficient species, as it can get into all those little crevices that we can’t reach ourselves.

Aside from being pretty cool to look at, this filefish is also a champion majano eater. The catch? It’s not considered fully reef-safe. Although it’s not expected to turn your tank upside down, it can bother some corals. It may also eat smaller aquarium shrimp and snails. In the end it’s up to you to decide whether that’s worth it for you or not!

Majano anemone prevention

It’s difficult to completely rule out any possibility of majano anemones making it into your tank on a piece of live rock. This being said, with proper quarantining of new materials, you can drastically lower the chances of it happening.

As mentioned previously, this species can move about in search of light, which they need for their zooxanthellae to photosynthesize, and food. If you quarantine a piece of rock that it’s hiding on, the culprit will eventually pop out in search of a brighter spot. At this point, you can take care of it using one of the methods described above.

Tkachenko, K. S., & Britayev, T. A. (2016). Unusually high abundance of the actiniarian Anemonia manjano Carlgren, 1900 outcompeting scleractinians in central Vietnam. Marine Biodiversity46(3), 545-546.

Vallejo, B. M., Aloy, A. B., Ocampo, M., Conejar-Espedido, J., & Manubag, L. M. (2019). Manila bay ecology and associated invasive species. In Impacts of Invasive Species on Coastal Environments (pp. 145-169). Springer, Cham.