Live Rock Hitchhikers; the Good, the Bad, and the Ugly!


A great way to seed a newly set up marine tank and to speed up bacteria growth is through the use of live rock. Within this post you will find a detailed list of a range of critters that you may find growing on your rock.  But DON’T WORRY they aren’t all bad, some can be a great part of your tanks clean up crew.



‘Live Rock’ by definition is not rock that gets up and moves around (Sorry if you got excited about that). The ‘live’ part of live rock simply refers to the life on and within the rock that will grow and multiply within your tank. Some of these critters are a valuable part of any marine aquarium however, some of them if allowed to over populate can cause issued within a reef tank.


So…can you see little critters moving around your rock? Wondering what they are? Worried if they are bad? Well below is the hitchhikers guide to the good, the bad and the ugly.



The Good


#1 – Feather Duster Worms



A very common type of small worm living in a tube found on the surface of live rock. They are beneficial critters that feed by filtering particles out of the water with their ‘feather’ like tentacles and are an indication of a healthy reef tank. They will pull back into their tubes if startled for protection.


#2 – Peanut Worms;



I remember the first time I saw one of these in my reef tank and freaked out. I had no idea what it was as it was a long worm like critter. Turns out it is a great addition to the clean up crew by eating left over food or detritus. A brown, cream looking worm in the shape of a peanut, hence its name.


#3 – Spaghetti Worms



Spaghetti Worms live in burrows on the rock surface and search for food with very long tentacles. Just like the feather duster worms, they are ideal in a reef tank as they scavenge uneaten food preventing it from rotting within your system. Although not a pest, some corals can be bothered by the worms tentacles. Simple daily observation of coral health is enough to notice any irritation by these worms.


#4 – Tube Worms



Easy to notice as they form long tubes on the surface of the live rock and are very similar to feather dusters. The main difference in how they feed (which is more like the spaghetti worm) as they use their tentacles to scavenge for food rather than filter feeding.


#5 – Limpets



Most likely you know you have these in your tank and simply want to know their name, as they are easily identified by their pointed shells. Most of these are harmless grazers and will do a great job at keeping algae at bay.

#6 – Stomatella Snails



One of our ugly hitchhikers but one of my favorite. This is only because one of my tanks had loads of them and they did a great job of clean the glass but don’t worry about them spoiling the view, they mainly come out at night. A great free and fast reproducing critter to find on your live rock.


#7 – Pods



Arthropods, Copepods, Isopods, Mysis, Amphipods, or simply known to many as ‘pods’ are all tiny little shrimp like critters that can come from your live rock. Copepods are one of the more common and most beneficial as many inhabitants of your tank will eat them providing a natural food source. Amphipods are slightly bigger and proving they don’t get to plague proportion are a good little scavenger. Many people buy pods (I know, as I do) as a natural food source for your reef but if you can grow them for yourself, even better.


#8 – Jackpot!!



Sometimes, just sometimes, you get really lucky with your live rock. I have heard of stories of people getting fish eggs, urchins, coral and inverts. Sounds great right? well most of the time it is, its free livestock in your very own reef tank but always get the identification on anything you find on your rock. Just to make sure they are reef safe.


#9 – Brittle Stars



One of the most interesting critters I got from live rock. Brittle stars are a type of star fish that are a great part of the clean up crew. Most likely the ones you have on your live rock will be the smaller more common type growing around an inch or two. They hide among the rocks and stick their arms out to reach for food. A great scavenger for any reef system and are generally known to be reef safe. I had dozens in my system and hope I still do but don’t see them all to often.



The Bad


READ THIS FIRST – when I say bad I only mean bad under certain conditions. If you find one or two small critters from this list in your tank don’t worry you don’t have to start again. When small and in low numbers, they can be a good part of the clean up crew. The issue is when these critters grow big and over populate the tank. If you find them early on when the numbers are low they can simply be removed, trapped or killed easily.


#1 – Fire Worm



When dealing with Fire worms show caution as they can give you a nasty sting so try not to handle them. They look a lot like a large bristle worm and they normally eat corals. If you spot this in your tank I suggest removing it with tweezers to prevent getting stung. It will most likely retract into the rock work but keep at it, as you don’t want to let it grow big.

#2 – Bristle Worm



Most Bristle worms when small are great little scavengers eating any leftover food or detritus. they look similar to the fire worm and can give a nasty if handled, so again show caution. As discussed above, the issue is when they get big as they become a very adaptable predator praying of small fish and other critters. I personally have a few small bristle worms in my tank form time to time but having shrimps and crabs in your tank keep there numbers under control.

#3 – Flat Worm



Flat Worms are a type of sea slug that are small, toxic and fast at reproducing. Some types may target corals and wipe out a coral colony if not kept under control or removed. There are many different methods of removal form manually picking out the worms, upping the tank temperature (Read more into this method before doing so)  and/or there are many types of treatments on the market that are designed to kill off this pest.


#4 – Nudibranch (Sea Slug)



I have a personal hate towards this critter. Many sea slugs look amazing in color but have a nasty side. The one in particular I had issues with ate all my zoa gardens and quickly over populated my tank. These are small slugs that need a keen eye to spot but its worth looking, trust me! Dipping Corals before placing them into your main display is recommended.


#5 – Aiptasia or Glass Anemone



A very unsightly anemone that can quickly reproduce and take over a tank if not stopped. They have a nasty sting and often sting coral and other inhabitants of the reef. If small they have little impact on fish and coral but they grow rapid and soon become a problem. But be careful when getting rid of them as if they feel threaten or you try to remove them from the rock they can release pores into your system. Each one having the possibility of becoming another anemone. As Glass Anemone’s are a very common pest there are many methods on the market and home methods available to use that are reef safe and easy to use.


#6 – Mantis Shrimp



Not the most common hitchhiker but we have the Mantis shrimp. A brightly colored predatory shrimp that will eat small fish. So not recommended in your average reef tank. However I have heard of some people who keep a species only tank as they are a very decorative invert.


#7 – Astera Starfish



For the most part these are harmless algae eaters and often look good moving around your tank however they have been known to munch on corals from time to time. As always the problems arise when their population grows. To avoid this you can simply pull out the starfish you see as they are slow and easy to spot. If this isn’t an option then you can introduce a fish/invert to control the population naturally, such as a Harlequin shrimp.


#8 – Disease


Now this isn’t exactly a critter or a pest but if you have got your live rock form a fellow reefers tank who has an illness in their tank, taking rock form their tank could transfer this disease to your tank. Although I personally haven’t heard of this happen to anyone I feel it cant hurt to mention it.



So there we are, a list of the good and a list of the bad but this list doesn’t mention every known critter that could be on your rock so if you have a pest problem and you can’t identify the critter from this list, then you can do one of two things;

Join reef-fin’s reefers and post your issue where fellow reefers will be able to help solve your problem or, contact me directly and hopefully I can help.