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/The Conscientious Reef Aquarist

Scavengers For Marine Systems

By Bob Fenner

One of the smaller sea cucumbers used as marine scavengers

New Print and eBook on Amazon

Marine Aquarium Algae Control

by Robert (Bob) Fenner

Oh for the saltwater equivalent of a Plecostomus; those piscatorial cleaner-upper sucker-mouth catfishes from South America. Wouldn't it be great to have a few of them for your marine system for nighttime tidying up and algae removal? Well, you don't have to break out your mad-scientist outfit to genetically engineer marine pleco's; yes, there are analogous organisms for saltwater use.

Here we'll survey what you can, should, and might do in the way of providing marine scavengers for your aquarium.


Does this mean you can chuck your algae pad, vacuum gear and hoses? Nay! Of course, the better designed, set-up and maintained systems require less elbow-grease than not, but still, the second law of thermodynamics rules: "All systems tend to a state of greater disorder"; i.e. things go to pot. The best thought out and executed live-holding outfit is going to need periodic checking, cleaning and water changes... the biological "helpers" mentioned here can do just that; aid you in keeping your system optimized; but woe be to those who would elect to do nothing more than feed their livestock. Their futures (and tanks) are clouded.

Various "scavengers" can be used as an adjunct to proper filtration, circulation and under-zealous feeding; they perform three primary beneficial functions: removal of detritus and uneaten food, control of algae and other excess undesirable growth, and "stirring up" the substrate, aiding in passage of water and more.

The Players:

Miscellaneous: "Live Rock and Live Sand"

The plethora of organisms that can be intentionally and/or accidentally introduced by way of LR and LS can be a real boon to marine aquarists. In a statement, such a mix can be the filter/food/homeostatic force of a system. The various worms, crustaceans, bacteria, et alia critters living in and amongst these substrates can do it all.

For several years our southern Californian service company was fortunate to have a series of tanks we "borrowed" gravel from that sported a mix of amphipod crustaceans (and who knows what else). We shared this about and had very little cause for using algicides, doing gravel vacuuming... Should you be so lucky as to know someone with such a helpful "mix", do beg a scoop of their biota.

Conchs and Other Scavenging Shellfish:

Tank cultured queen conchs, Strombus gigas are available for use in marine aquariums; suitably sized individuals scrounge around and through the substrate (and sides to a lesser extent), removing epiphytic green algae and diatom scums. Unlike their freshwater brethren, conchs will not "reproduce like rabbits" in your tank; but can reach a prodigious size of ten inches in the wild.

Without ancillary feeding one per approximately each four square feet of bottom's about right; if more crowded, or you're looking for noticeable growth, purposeful external foods are required.

Snails of different types (turbo, Astrea, periwinkles...) are plugged for use by many writers and aquarists. Be aware that there is a large range of suitability amongst species and stocks of these gastropods... read up for sure, and confirm that the specimens you're dealing with are "live" and healthy when purchased.

Some authors endorse the opistobranch snails called Seahares (Aplysiaceae) for marine clean-up duty; I do not. Most specimens offered are cool to cold-water, promptly die in tropical systems and often take the rest of the tank with them.

Other variously efficient mollusks include murex (whelks), Chitons, cowries, abalone (for temperate systems) and more.

Though they will live on hard bottoms, some (live) sand is appreciated by all these mollusks. General, stable "non-vertebrate" water quality conditions suits them just fine.

Purposeful Crustaceans:

Hermit crabs, some much more desirable than others, are the cause celebre of crustacean cleaner-uppers. Other crabs, lobsters and shrimp are opportunistic omnivores, needing to eat meaty foods, not "leftovers" or detritus.

Seek hermits that are smallish and active. Many internet-aquarists root for hairy-legged varieties, especially red and white "haired" types. If your dealer doesn't stock these, they may be easily mail-ordered.

The Spiny-Skinned Animals:

Stars, Brittle and Otherwise

The Seastars and brittle stars span a broad range of suitability for marine aquarium use. You must be sure of the requirements and habits of those you have to choose from... and their vitality. For the former seek out microphagous species of starfishes; ones that feed on detritus. The family Ophidiasteridae (e.g. Linckia, Fromia) reign supreme in this category. Other macrophagous carnivore types are to be avoided for clean-up duties, especially as they will eat shellfish, Anemones and more.

        The Brittle or Serpent Stars are grouped as the Class Ophiuroidea, characterized by having highly mobile arms that can be used to assist in (relatively) rapid motion. These starfish-like echinoderms are decidedly quicker and more delicate than asteroids. Their common name is derived from their sinuous, snake-like movements, and the fact that they're truly brittle and break away easily if they come under attack. The podia in this class are generally used as sensory organs, rather than for active feeding as with their kin, the asteroids. There are more than 2,000 described species worldwide, and they're found congregating throughout shallow reef environments, hiding under rocks and within and between other living organisms. A Green Brittle Star, Ophiarachna in captivity. This animal is often becomes a fish predator with growth/size.

Brittle stars have the same good/bad choices amongst them. My strong advice is to seek out smaller individuals of species that stay small. Brittle stars are nocturnal and require a dark space to hide during the light of day; they are active scavengers at night, and are not opposed to ingesting sleeping fishes they can get their legs on.


I'll admit that urchins are not my generally favorite type of marine scavenger; though many are hardy, long-lived and interestingly shaped and colored.

They come in many types, sizes and degrees of spininess. My choices are ones with more "clubbed-shaped" spines, the so-called sea mines, pencil, or club urchins. Longer spine varieties offered in the hobby (mainly the genera Diadema and Centrostepanus) are a little more prickly (I couldn't help myself) propositions, presenting a danger to sticking you and your other livestock.

These urchins can be purposely fed any meaty foods by dropping same near their spines. Their do however have two downsides; occasionally they get stuck (or seemingly so) in hard to extricate places. When and where in doubt regarding this, don't overreact; let a few days go by and you will probably find your urchin has rescued itself. Secondly, urchins are venomous; no that's not a mis-print; even the short "pin-cushion" and club-spined varieties bear "poison tube feet". Handle urchins only with a sturdy net, not bare hands; and don't lift them into the air (i.e. bag them underwater).

Mespilia globulus (Linnaeus 1758), the Blue Tuxedo Urchin (Sphere Urchin of science). Eastern Indian Ocean to western Pacific... in shallows amongst algae it grazes on. To three inches in diameter. Needs hard substrates, shady areas. Can be kept solitarily or in small groups. Eats mainly algae, including corallines. 


Gadzooks, Seacukes! I mention these more to warn against their use than to encourage it. Yes, sea cucumbers are neat; some like sea apples are gorgeous; Yes, they are low-maintenance... but also, yes, they can, will pollute your system quickly and thoroughly if "annoyed". Such annoyances can take the form of disturbance by a piscine neighbor, a water change, or being pushed/pulled by a circulation device.

I've seen it many times; the cuke unfolds one or more defense mechanisms; eviscerating and/or utilizing chemical poisons, and the whole tank is bouillabaisse.

Handle sea cucumbers with care or not at all.

Echinoderms in General:

The issue of selecting healthy spiny-skinned animals is a matter of avoiding bunk species and good ones that show signs of tissue necrosis (white, soft, or missing areas of the body), and loss of the hollow tube feet. Worthwhile stars are active, out and about at times, looking for food.

Marine Catfishes:

The families Plotosidae and Ariidae are principally saltwater, but more akin to the North American freshwater catfishes (Ictaluridae) in their feeding habits. That is, their more like suck-em-ups than cleaner-uppers when it comes to food, eating meaty items and avoiding algae and wastes. Besides, marine cats are painfully venomous. Safely keep them for their display sake, not as scavengers.

Other Fishes: There are MANY

Shrimp Gobies: Many folks use these fishes to keep their substrate stirred in reef systems. Be aware that they are all-too often lost to outright starvation. Each specimen probably needs at least a couple to four square feet of vibrant live substrate to provide forage.

Here is a too-thin Cryptocentrus leptocephalus.

Problems With Using Marine Scavengers:

Mysterious Death Effects:

Predatory tankmates should be studied in advance of scavenger placement; parrots, Pufferfishes, triggers and their relatives the filefishes, et al. are notorious for picking on any and all novelties.

As with the "cost of democracy", the expense of marines is "constant vigilance". As usual, you will have to keep an eye and mental note open for your scavengers; difficult as many are secretive and nocturnal. See below for comments on feeding and act accordingly.

Copper and Other Treatments To Avoid:

If you haven't heard it enough from me or other folks, here it is again; don't treat your marines in your main/display tank. Period. Either upwardly adjust your water quality to favor your desired livestock, tough it out, or best, move them to a controllable hospital/quarantine system.

All medications, whether specified or not, are deleterious to non-vertebrate animals. You will either have to remove them permanently from the system or treat the fishes elsewhere.


As with the incorporation of "cleaner-uppers" in freshwater set-ups, it is imperative that, well, the scavengers have something to eat! The obvious and most practical means of providing adequate food is to install them last, after a few to several months after the tank is up and running.

When/if your scavengers seem lethargic, losing color, and in the case of non-vertebrates, body parts, do the following: 1) Check water quality and adjust, possibly via 2) A massive water change... maybe thirty to fifty percent, 3) Offer some food directly to the animal; and lastly 4) Remove it/them to a separate hospital/quarantine facility for re-constitution or loss.


The key to successful marine aquarium keeping is proper set-up and maintenance. An optimized system is first and foremost designed, put together and operated properly.

The utilization of biological scavengers by itself will not go nearly far enough to grant you an upkeep-free system; but their appropriate use can go a long way in keeping the algae and detritus in check, and the substrate stirred up... besides that, many of these animals are interesting and beautiful in their own right.

Considering their needs, demands on the system, possible growth and negative consequences of inexplicable death, these aqua-janitors may be well worth the try.

Bibliography/Further Reading:

New Print and eBook on Amazon

Marine Aquarium Algae Control

by Robert (Bob) Fenner

Burgess, Warren E. 1977. Sea urchins. TFH 1/77.

Campbell, Marti 1996. Editorial on the use of farm-raised Caribbean queen conchs. FAMA 9/96.

Ellis, Gerald R. 1982. Echinoderm scavengers. FAMA 9/82.

Fenner, Bob, 1995. A diversity of aquatic life: Spiny-skinned animals, phylum Echinodermata. FAMA 5/95.

Fenner, Robert, 1996. Look, but don't touch! Marine catfishes of the family Plotosidae. TFH 7/96.

Hopmann, J.A.M. 1977. A bad experience with sea cucumber caviar. Aquarium Digest International 4(77).

Mancini, Alessandro, trans. by Paolo Macedone, 1991. Starfishes in tropical marine aquaria. TFH 9/91.

Miklosz, Joan A. 1972. Scavengers, part 1-3. Marine Aquarist 3(1-3):72.

Volkart, Bill, 1989. Sea cucumbers- the ugly invertebrates. TFH 2/89.

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