Invertebrates (or often just called inverts) are an often overlooked category of livestock in reef tanks. Understandably, most people think of fish and corals first, but inverts offer a pleasantly surprising variety of interesting and helpful creatures that add even more to enjoy to any reef tank. This is often most appreciated in smaller tanks after just a few fish fill them up. At that point, the attention can shift to inverts since you can still add quite a few without overstocking.
Algae Control
Even if inverts are not appealing to you at all, they still provide an essential role in every reef tank: algae control. One common theme to every reef tank is algae control, and inverts are an essential part of bringing balance to algae control. Snails and hermits provide this essential role and do so very effectively.
Snails
There are lots of snails to choose from. Some are cheaper, some are larger, some are better at not getting stuck on their back, and some can actually reproduce in a reef tank.
Astrea snails provide none of these benefits except maybe being the cheapest. They often get stuck on their back, don’t usually reproduce in a reef tank, and aren’t unusually effective at eating any algae in particular. They’re fine to have, but are not what I would do out of my way for. When other options are available, I’ll usually go with the other options. That said, they’re still pretty good, so I don’t avoid them, I just don’t go out of my way to get them.
Turbo snails get very large which can make them more effective than the average individual of another species. However, their large size means they’re more likely to end up knocking frags loose and off the rocks, so this is something to keep in mind.
Trochus snails are good at eating algae, can reproduce in a reef tank, and are usually good about getting themselves turned upright if they fall on their backs. In general, they would be my top choice for a snail.
Nassarius snails aren’t an algae eater at all, they’re a scavenger that stays in the sand all the time unless they smell food at which point they all come out and it looks like a zombie uprising. Nassarius snails are great at helping to keep the sand bed healthy. Smaller types are good, but I highly prefer the larger Tonga nassarius snails. They look cooler and their size makes them more effective at keeping the sand stirred.
Margarita snails aren’t as popular anymore, thankfully, because they prefer cooler water and tend to die sooner or later in reef tanks. Don’t buy them if you see them available.
I usually aim for at least three snails per 10 gallons, but don’t hesitate to get more if they aren’t keeping the algae in check. Depending on how the tank is running and how out of control the algae is, going with as many as one per gallon may be needed.
Hermits
Hermits are great too, but they do have a couple issues you should be aware of. One is that they will kill snails for their shells if they don’t have enough empty shells around. Because of this, I usually try to keep A LOT more snails than hermits, as in 5-10x as many snails as hermits and lots of empty shells. Also, they can’t climb the glass, so you still need a lot of snails to keep the glass looking good.
That said, hermits can be REALLY good at eating algae. In general, I prefer the larger types. Even though they tend to be more expensive, they are much more effective due to their size.
Scarlet hermits are really good at eating hair algae. They’re also a bright cherry red and medium in size, so they look nice too.
Orange knuckle and blue knuckle hermits are both jet black with very bright bands at their knuckles, either in orange or blue, obviously. They are medium to medium-large and look really cool. They are pretty good at algae control, but not the best, so if you have a major algae problem, go with scarlets first. They also tend to be more expensive ($8-15 each as opposed to $1-6 for most others), so I tend to only get one or two of each. The orange knuckles are sometimes also called Halloween hermits, but I reserve that name just for the ones described below since they aren’t known by any other names.
Halloween hermits are different than the orange knuckles. They have thin orange and burgundy stripes. They are also shaped differently than other hermits, they are longer and flatter and use a completely different type of shell because of this. Not only are they unique looking, they are a great scavenger in addition to being a good algae eater.
Other Hermits – The Tiny Ones
Depending on how many hermits you want and your tank size, you may want to include some of the smaller hermits such as blue legs, red tips, etc. I tend to avoid them because I’d rather buy one larger one instead of 5-10 smaller ones to get the same effect, but don’t hesitate to include them if you like them, have a smaller tank, etc.
Shrimp
There are a few shrimp that are popular and worth keeping. Most are quite hardy for inverts, easy to get eating, and don’t bother anything.
Scarlet skunk cleaner shrimp, usually just called cleaner shrimp, have bold red and white stripes on a gold body. They are a true cleaner shrimp (indicated by their white antennae, that’s their advertisement to let fish know they are cleaners). They are the most likely to be out in the open and will usually clean your hand if you put it in the tank and hold still in front of them.
Fire shrimp are a bright cherry red with white legs, a few white spots, and white antennae. They are usually much more reclusive than the skunk cleaner shrimp, but their looks are much better, so the reward when you do see them make them worth having too.
Peppermint shrimp are more subtly patterned and not cleaner shrimp. They are more reclusive than the skunk cleaner shrimp, but not as bad as the fire shrimp. Most people buy them because they eat aiptasia, but they usually aren’t very good at this. I’ve heard there are three species of peppermint shrimp common in the industry but only one reliably eats aiptasia. There is a pattern difference to identify the correct species, but I can’t find it right now (I will update this article with a link when I come across it again).
Harlequin shrimp are sure to get your attention when you see them in a shop. Their bold pattern is certainly remarkable. Unfortunately, they require a diet of live sea stars. If your tank has been overrun with asterina stars then you may not mind. Otherwise, you’ll be forced to buy a chocolate chip star for them to paralyze and slowly eat over the course of a couple of weeks or so. This isn’t appealing to me at all, so I’ve always avoided them completely, as tempting as they can be.
Pistol shrimp are a neat addition, especially if you pair them with a compatible goby. They are pretty small and although they are capable of a destructive “blast” from their modified claw, they tend to be great, well-behaved members of a reef community. Be careful about the rockwork though, along with the goby, they can easily undermine all the sand from below your rock and allow it to shift and even tumble. Make sure your rock is firmly resting on the bottom of the tank, not just the sand.
Porcelain Crabs
Porcelain crabs are one of my favorites. They’re one of the hidden gems that tend to hide, but that makes it that much more rewarding when you see them out. They are filter feeders that hold their fans out in the current to collect food (just like freshwater bamboo shrimp). They also have cool colors. They are cheap, but even in stores they are easy to overlook because of their reclusive nature, so be sure to ask about them.
Reef Lobsters
These are another one of the my favorites. There are two main types, the red and the purple. The purple stays smaller at around 3-4″ whereas the red can hit about 6″ or so. Both are relatively peaceful, but they are still capable of going after fish if they really want to, especially if the tank isn’t fed a lot to begin with. If there is enough rockwork and caves for fish to avoid them and the tank is fed well, they tend to not put in any effort to catching anything.
Tube Anemones
These are yet another really cool invert that can be a very interesting addition to the right tank. The problem with them is they can eat fish. Most fish tend to avoid them though, so this really shouldn’t be a problem. My Banggai cardinals bred in the tank and although a few babies made it over the overflows and into the refugium, I’m almost certain the vast majority of them were eaten by the tube anemone. In nature, Banggai cardinals hang out in anemones and urchins for protection, and since a tube anemone looks like a cross between the two, it’s no wonder the babies would have dove straight into it thinking it was protection. It wasn’t.
Tube Anemones have some of the absolutely brightest colors you will find on anything in a reef. Under the right lighting, the inner tentacles can look like they are producing light.
They are burrowing and create a tube for themselves in the sand that they make with their own slime excretion. They prefer deeper sand, but mine was happy in the 2″ or so I had in the tank.
They are non-photosynthetic, so they need to eat well. The good thing is they are happy to eat just about anything they can grab. Mine would eat frozen foods and would go crazy if I fed pellets directly to it.
Scallops
Flame scallops aren’t too common, but they’re really nice looking if you see one, especially the electric flame scallop that has an iridescent edge to its mantle that it moves in a way that you will swear is electricity running up and down it. Unfortunately, most flame scallops don’t get enough to eat so they slowly starve over the course of a few months to a year. This may not be an issue if you have a well-fed tank with a lot of food going in and feeding a lot of livestock. This is the only time I would try one. If you do, place it in the downstream end of your tank so that food gets pushed toward it by the flow.
Fanworms
Like flame scallops, fanworms such as feather dusters tend to slowly starve in most tanks and should be reserved for tanks already getting a pretty heavy feeding routine.
Sea Stars
Unfortunately, most sea stars don’t do well in reef tanks. Chocolate chip stars aren’t reef-safe. Linckias don’t tend to last long, they are extremely sensitive to exposure to air and tend to not last more than a few months which usually indicates a dietary deficiency.
Sand sifting stars are an exception and tend to do well, but they also disappear to never be seen again which isn’t what most people like spending their money on.
Asterina stars are small beige sea stars about an inch in diameter that some people consider pests. In my experience, they will rarely bother anything. The worst I’ve ever seen myself is if they cross a colony of zoanthids or some other coral, the coral will close just like it would if anything else touched it. If you see one just sitting on a coral and it looks like it may be eating it, move it off the coral or completely remove it from the tank. I’ve heard there are multiple species that look almost identical and only one is a problem. So be aware that they could potentially do some harm, but I’ve never had any issues. Some people also have them get completely out of control, but again, I’ve never had this problem. If you do have this problem, you can manually remove them (they’re easy to catch after all) or get a harlequin shrimp.
If you come across any other sea stars that catch your eye, do some thorough research before buying it, there’s probably a reason they’re not highly recommended.
Urchins
Urchins can be good, certain species such as the pincushion and tuxedo stay relatively small (3-4″) and eat algae. Others such as the longspine get very large (over 1′ in diameter) and shouldn’t be considered for anything other than a very large tank (180-gallons bare minimum). Be aware though, the size of some urchins means they will knock things over just like a large turbo snail will. Some also pick up things to decorate themselves, and this may include your frags.
Sponges
Yes, sponges are animals. They are the simplest of all animals. In general, I wouldn’t get any except the encrusting types. Fortunately, they come in a wide variety of colors as shown below. They are non-photosynthetic, so they need to get all their food from the water column. They are best kept under an overhang so that algae doesn’t grow on them but they are still visible to you and get flow which provides them with food.
There is literally nothing else to their care. They are pretty hardy. Ideally, they shouldn’t be exposed to air, but the few times I’ve exposed them accidentally, they were fine. They can be easily fragged and spread if that’s an issue, but they’re usually best kept on the rock you get or find them on.
I highly recommend you do not try and of the non-encrusting sponges, their track record in captivity isn’t good. They seem to need a lot more food than most reef tanks should have, or a different kind of food entirely, so don’t be tempted.
One possible exception is the spider sponge which is spectacular looking with a branching orange sponge laced with pure white non-photosynthetic zoanthids. This is still a very challenging option, but they have a decent chance if the tank is large and is fed a lot.
Pineapple sponges are very small, around 1 cm tall, white to cream sponges that usually show up from the live rock. They are usually one of the first “Hey, I found this on my live rock, what is it?” things that people find. They are usually in protected areas with little to low light. They are good, they are filter feeders and don’t bother anything.
More Information
For more in-depth information as well as entire chapters on live rock, refugiums, and more, you can’t do any better than Reef Invertebrates by Anthony Calfo and Robert Fenner. The only issue I found in the whole book is that at least one of the authors seems to have a personal vendetta against aquacultured live rock, which I found to be very inaccurate. Other than that, the book is outstanding and I can’t recommend it enough.
Find it on Amazon