By Skeet & Kathryn Polk
Most reef hobbyists have noticed something out of the ordinary appear in their tank (i.e. something they didn’t put in there). Often known as hitchhikers, many small critters move into new marine aquarium ecosystems through live rock and coral. Some are undesirable and can be harmful, while others can be beneficial. Many are detrivores, which consume leftover food in the tank. This guide intends to help hobbyists identify different types of hitchhikers, with advice for how to respond.
Table of Contents (based on desirability): More hitchhiker info below
Not a problem (some can be beneficial): Brittle Starfish, Serpent Starfish, Bristle Worms, Amphipods & Copepods, Tubeworms, Feather Dusters, Sponges, Acro crabs
Cautious (potential to harm): Astrea Starfish, Snails, Sea Urchins, Pistol Shrimp, variety of crabs Astrea Starfish, Snails, Sea Urchins, Pistol Shrimp, variety of crabs
Threat (undesirable): Flatworms, nudibranch, Aiptasia, Mantis Shrimp, Gorilla Crabs
Astrea Starfish: (Cautious) Little white starfish (see pics below) that can be a nuisance because they quickly multiply in a reef tank. What to do: I do not appreciate them in my reef tank, and suck them out during tank cleanings and water changes.
Brittle or Serpent Starfish: (Ok) Can vary in size. Identified by five long skinny legs coming from a center disc. Moves about the aquarium with its legs consuming detritus and cleaning tiny crevices and sandbed. What to do: Let them be
Bristle Worms: (Ok) Although tainted with negative stigmatism, bristle worms are very beneficial to the home reef tank. They spend their time cleaning decaying biomass in the sandbed and rockwork. When we come in contact with them by moving things in our tank they release their “bristles” and get caught in your hand or perhaps a fishes mouth.
Flatworms: (Undesirable) Will eat coral. What to do: treatments like Salifert Flatworm Exit is a reef safe choice that kills most types of flatworms and is rather easy to administer.
Amphipods & Copepods: (Great) Desirable detrivores that your fish will love to be able to feast on. These microscopic feeders signify a healthy marine ecosystem.
Snails: (Cautious) need to be watched because several species will consume coral. What to do: unless added with a cleanup crew or positively identified it would be best to remove while you can see it.
Nudibranch: (Undesirable) looking similar to a sea slug, without proper identification should not be trusted. Most Hitchhiker nudibranch in my experience has been undesirable. What to do: Some types of predatory wrasses will actively hunt and eat nudibranchs. Depending on size they can be manually removed with tweezers or siphon tube. If suspected on coral and can be removed the coral can be dipped with a coral dip like TLF ReVive or CoralRX dip.
Tubeworms: (Ok) filter-feed, somewhat cleaning out the water. Some, however, get very sharp and can cut your fingers if you pick up a piece of rock with a lot of tubeworms. What to do: Leave alone unless multiplying too fast. Some types of fish will eat them to control them, namely predatory wrasses.
Feather Dusters: (Ok) Filter feeders. Best left alone.
Sea Urchins: (Cautious)Sea Urchins can get very big and knock over rocks. They can also consume coralline algae, which is not necessarily a bad thing. What to do: manually remove if desired before or after it becomes a nuisance.
Sponges: (Ok) a filter-feeding sponge does no harm to a reef tank habitat. What to do: Besides rapidly growing most sponges are harmless and add as biodiversity and filtering aspects to our reef tanks. It is researched that some sponges actually contain symbiotic bacteria that live on phosphates.
Aiptasia and Mojano Anemone: (Undesirable) Can sting corals and other living organisms. What to do: the natural addition of peppermint shrimp is the preffered method of removing aiptasia. These shrimp target the aiptasia and actively consume it, tearing it from the rockwork. Berghia nudibranchs can be used to consume aiptasia but in my experience are expensive and not very effective. Products like Red Sea Aiptasia-X, Mojano wand, and other aiptasia eliminating products are available with variable success.
Pistol Shrimp: (Cautious) They are active sand movers, but can be interesting if housed with a shrimp goby. What to do: unless desired in aquarium they can be removed by building a trap. Take a small plastic bottle and cut the top off and flip inward. Glue the top inside the bottle. Your contraption should look like a minnow trap. Place some small rocks or substrate to weigh down and bait with fish food. Empty food daily and check for critters trapped and try again. This method can be used for various size fish to small inverts by controlling the size of the opening.
Mantis Shrimp: (Undesirable)Will kill fish and inverts, and could break the glass of your aquarium. They are extremely fast and incredibly strong. What to do: remove with trap method. If you have an acrylic aquarium they are fascinating creatures to observe as they grow but will need to be fed live crabs.
Crabs (multitude of varieties): (Cautious) Anything but an acro crab is probably undesirable. Most crabs will eat coral or small fish.
- gorilla crabs– (Undesirable) Identified by black tip claws and hairy shell. These crabs will burrow into corals and destroy or eat them. Always best to remove crabs. Inspect corals before placing into aquarium. All corals are dipped upon arrival at Coastal Reef and removed of any unwanted pests. It is best to dip corals between transfer of tanks to best minimize the transfer of unwanted pests.
- acro crabs- You will find these crabs living in the tight branches of SPS corals. They live in symbiosis with the host colony coral, using its tight branches for shelter while actively cleaning and moving over areas that can become stagnant within the growth of the coral. Leave these crabs alone, they are beneficial to the host coral.
I am sure there are many more! Can you think of any reef aquarium hitchhikers that we missed?
This blog is managed by Coastal Reef Employees, Skeet & TJ
Skeet, owner of Coastal Reef, formerly known as Majestic Reef, has been a hobbyist for the past 10 years. He has expansive knowledge and expertise, providing valuable advice to customers for over 8 years in Wilmington, North Carolina—even when his advice goes against making a sale or larger profit.
TJ is a highly reputable saltwater aquarium hobbyist as well, with a double-degree from UNCW in Marine Biology and Chemistry. With more than 4 years of retail aquarium experience, Coastal Reef is proud to welcome TJ back to our team.