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10 Most Surprising Aquarium Hitchhikers (Good and Bad)


By Bob Fenner


      Let’s face it, sometimes surprises can be fun; you know, like unexpected birthday parties. As aquarists though, incidents where “freebies” coming in and on other new purchases, rarely elicits squeals of “oh joy”! Most such hitchhikers are unwelcome guests; causing sprints for online help and guru advice on how to remove them. I urge you to not be over-hasty; in most cases these “bonus” organisms aren’t immediately dangerous… well, and to do the usual isolation/quarantine of all new livestock (including live rock and sand) to ferret out undesirables; otherwise starve them into revealing themselves, and granting you the opportunity to control them BEFORE introduction to your main/display system/s.

            Like going to the dentist, it’s so much easier, even fun to chat about these hitchhikers, rather than to have to deal with them ourselves. Herein is my take on the most surprising marine aquarium hitchhikers; with notes on their control and possible elimination.


Wherefore Art Thou HHs?

              First off, as you likely know, there are literally no ends of co-travelers with the livestock we acquire. For our purposes here we’re going to omit infectious microbes and parasites (thank you), and focus on the likely macro-life folks have to deal with saltwater hobbyists.

Principal Sources: Hard Substrates

            Anything wet can be a vector for introducing a hitchhiker to your system; yes; anything wet. By propensity and diversity of such introductions though, nothing exceeds hard substrates as diaspora media. Live rock, live sands, hard bases that stony, soft corals, gorgonians and more are shipped with are the super bonus of HH origins.

Oh so subtle, even sublime, as it lulls you into a false sense of security. Live rock and sand… actually any hard material collected in the wild, or not… that has been exposed to material collected in the wild may well harbour snails, worms, crustaceans, algae… and MUCH more.

     All new purchases should be isolated, quarantined for a few weeks: to give you time to examine for HHs, starving them out to reveal them. Besides, some curing may need to process.

 Unless the live rock is man-made, artificial, it WILL have other life coming on and in it. Here is a view of some of the area where Walt Smith International produces their artificial product. They are also the largest provider of the wild product; and do a thorough job of cleaning and spritzing newly cleaned rock to remove the bulk of hitchhikers. I’ve seen literally pounds of worms under their rinse troughs, and all other marine fauna found in shallow water, including moray eels!


Worms! Tah Dah; Let the Games Begin!

Vermes! Almost all phyla of worms can be imported along with hard substrates: From our fave Bristle- aka Fire-worms (Errantiate Polychaete Annelids); these can also start small on immotile invertebrate purchases (oh boy!). Below, a HH on a nice gorgonian, an Amphinomid out for a hike, and some small species doing their thing in aquarium substrate, and out and about on the surface.

In the mid eighties to about the latter 1990’s hobbyists were inclined to lose their proverbial minds re the presence of these spiky segmented worms. In actuality, unless there are too many, or they’re too large to get along with your other livestock, Bristleworms are more beneficial than harmful; so, hitchhiking worms can be a very good thing. IF you have too many, there’s something wrong with your operation/maintenance. Mainly, too much food is going into the system. Vacuum the substrate, move the rocks if need be to get around them, consider baiting, trapping and removing a portion of the wormy herd; and don’t fret. Oh, do watch your hands… those podial spines are the Dickens to get stuck by.

     Hard to avoid having at least some worm life in a healthy marine system; so… isolate new hard substrates, bait out too large specimens, and don’t sweat the small ones.


Algae: Some Good, Most Innocuous, a Few….

Algae are everywhere in aquatic environments; coming in and on hard substrates, in water with other livestock, heck, even as spores thousands of miles from oceans. Most are good news; using up, accumulating nutrients, some of which are otherwise or become toxic metabolites, synthesizing them into food for Protists to Vertebrates. What you want to be aware of is the settings which drive desirable forms and the ones that allow proliferation of undesirables, like most blue greens; aka Cyanobacteria. Immediately below, a mis of mostly Green, Red and Brown macro-algae species in Cozumel. Below lower; principally desirable encrusting Reds (Corallines) and next to it slimy, unwanted BGA, which can be red, brown, green….

High, consistent biomineral (Calcium and Magnesium mostly) and Alkalinity are key to promoting wanted over unwanted algae situations; coupled with competition from other purposeful photosynthetic life you keep, restricting the introduction coupled with export of excess nutrients, and use of specific algae eating organisms are the overall equation to balanced systems. IF your system gets out of balance; low RedOx, skewed chemistry, pest algae proliferating, look to your water quality, maintenance practices of set up period. Consider adding a DSB, macro-algal culture in an RDP refugium setting…. Stepping up your water change and gravel vacuuming programs.


Whose That Snapping Up My Wall?

Oh, let’s have a grouping of the big three groups of less than desirable Crustaceans that too often hitch a ride in with other hard substrates: Yes, it’s not Rice Crispies snap, crackling and popping unfortunately; but Crabs, Pistol Shrimps and Mantis that all-too often are hiding out by day, scouring your system stealthily by night, eating your other livestock! At right, a Mitrax forceps coming out at night in Bonaire. Below; good-looking for still a Pistol, Alpheus soror, and a nice Odontodactylus scyllarus in the wild.

Best to be on the look out for these jointed legged critters when you introduce hard items, and to still keep vigilant as your system matures. Their easily excluded through quarantine of new materials, and most can be otherwise baited and trapped in an up and going tank.




Snails, like the insects that are beetles are faves of creators, there being so many species of them. Though most are no trouble in captivity, some coming in on live rock et al hard materials are overtly predaceous, even potentially dangerous to you, the hobbyist. Experienced reefers will be familiar with Heliacus, Box or Sundial Snails; and other predaceous species. How ‘bout the one at right? Yep; this is a Textile Cone; Conus textilus; a fish eater and dangerous to humans.


Even Spiny Skinned Animals?!!!


Most folks don’t object to a freebie sea urchin, but some HH seastars can become population bombs in their own right. To wit, the oh-so-cute Asterina stars (at right) and some brittlestars (Ophiocoma, below). Little appreciated is that Ophiuroids are definitive animals in shallow to abyssal seas, often determining what other life can and does live there. You don’t want too many of these. Bait/trap them out by night and/or physically remove them.


The “Pro” Side of Hard Substrate Hitchhikers: MANY!


Cheer up sunshine; it’s not all gloom and doom when using natural live rock, wild-collected live sand and attached immotile livestock. Very many good microbes, aerobic and not, algaes of all sorts are introduced there in. Some of our faves include encrusting Red algae (as at right); all Divisions (the botanical equivalent to animal taxonomy’s Phyla) are found on and imported with hard substrates; and most all with fresh natural seawater.


Though most all of it is intentionally removed by hammers and high pressure water, a huge part of marine environments biota are sponges, Poriferans; ubiquitous filter feeders of the seas. They’re specifically removed to reduce fouling from their passing in transit, but… some almost always survive handling, boxing, shipping… and will resurrect themselves given propitious circumstances (good water quality, stable conditions). Here’s a mix on rock in Nuka Hiva, Marquesas.

Cnidarians; mostly called “corals” by hobbyists, are similarly removed from wild-collected live rock; mostly to comply with country and international (CITES) stipulations. Indeed, some LR purveyors list their shipments as “Misc. Scleractinia” to avoid confiscation should some small colonies pass undetected by their staff. As with die-backs in your system, even just a bit of tissue can recover under good care. Here’s an apparent stony coral skeleton… in Wakatobi, S. Sulawesi.


Ascidians; aka Sea Squirts along with sponges make up about half the biomass on and in live rock. Again, they too are “whacked off” in processing the rock for shipment, for the same reasons as Sponges…. And this is a great shame. This “almost vertebrate” life is very beautiful and interesting biologically. IF you can get “very good/fresh” live rock, you may find live Sea Squirts popping up on it in time. Here in N. Sulawesi, Indo.



More Specialized HHs:

Heck; we’re running out of time and space! Am desirous of listing Waminoa species flatworms as they’re so common; occurring on many species of stony (here on Plerogyra on the right) and soft (on a Sarcophyton below). As with Bristleworms, folks used to lose their minds on encountering these. Again, here comes the pitch for isolating all incoming…. And if you have a bunch at stake, or are in the biz, using preventative dips/baths to prevent introducing these dang pests. Too late? Siphoning them off their hosts, the rock, substrate helps… there are some natural predators (mostly small Labrids), and though dangerous to use, Anthelminthics that will poison ALL worms, and possibly other life… that one can use. Be ready to do massive water changes should this use poison your system.


Got Giant Clams? Maybe Pyramid Snails As Well!

Pyramidellid snails can make their way into a system on other hard materials, but most all are errantly introduced with infested Tridacnid Clams. Oh yes; they’re no fun. Again, best excluded by careful isolation of new Clams, examination of their byssus area, and cursory removal with sharp forceps in processing ahead of their introduction to main/displays. There are predators that will eat these pest snails, but they can easily damage the byssus, possibly killing the clam.




            Where are the rest?! Where are the Red Bugs, the Coral Eating Nudibranchs; this can’t be all? Well, actually…. The above accounting may well not be surprising to you; and for sure there are MANY more hitchhikers we could chat about. Don’t fear the Reaper or them. Instead, get and use a solid quarantine protocol to keep most out from the get go; and be aware of what to look for in the way of accidental introduction; sensible control. As with other aspects of marine aquarium keeping, nothing good happens quickly with hitchhikers.


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