Mention a reef aquarium clean-up crew and most hobbyists immediately picture trochus snails, hermit crabs and perhaps a few nassarius snails emerging from the sand at feeding time.

They are excellent animals.

But the reef has a much larger maintenance department.

Some members wear armour. One looks like a slug that forgot most of its shell. Another carries pieces of your aquarium around as camouflage. One spends its life swallowing dirty sand and returning it cleaner. And another has essentially one item on its menu:

Aiptasia.

A well-designed clean-up crew shouldn't simply contain more animals. It should contain animals performing different ecological jobs. Algae grazing, scavenging, sand processing and pest control are separate niches, and stocking animals according to the work actually needed is generally more sensible than buying a predetermined "crew per gallon." An oversized clean-up crew can also exhaust its food supply and starve. 

Here are some of Reefing Canada's favourite candidates for the reef keeper who wants to look beyond the usual suspects.

If one suddenly races across your rockwork at night, your first reaction might be:

What on Earth is that?

Stomatella snails look more like sea slugs wearing tiny fingernail-shaped hats than conventional snails.

And they're remarkably useful.

Their reduced shell and elongated body allow them to reach cracks and surfaces that bulkier snails often miss. They graze microalgae and biofilms and are particularly active after dark. 

Some populations will even reproduce successfully in reef aquariums. 

They also have a rather extraordinary escape strategy.

If attacked, a Stomatella can shed part of its tail—much like a lizard—and regenerate it later. 

Best job: Microalgae and biofilm in hard-to-reach rockwork
Cool factor: ★★★★★
Watch for: Predatory fish and crabs that may find them delicious

Despite its somewhat alarming name, a fighting conch is generally a peaceful reef resident.

Its specialty is the surface of the sandbed.

Using its long, flexible proboscis, it searches the substrate for algae, detritus and edible organic material while its movement disturbs the upper layer of sand.

And then there is the way it moves.

Rather than gracefully gliding like many snails, a conch can use its strong operculum almost like a lever, pushing or occasionally launching itself forward.

It looks slightly ridiculous.

Which makes it even better.

Fighting conchs need usable open sand and enough food to sustain them; supplemental feeding may become necessary, particularly in smaller or exceptionally clean systems. 

Best job: Sand-surface maintenance and scavenging
Cool factor: ★★★★★
Watch for: Tanks without enough open sand or natural food

Few clean-up crew animals combine usefulness and personality quite like a tuxedo urchin.

These compact urchins steadily graze algae from rock and glass and can tackle surfaces that some snails leave behind. 

But eating algae isn't what makes them unforgettable.

Tuxedo urchins decorate themselves.

Using their tube feet, they pick up rubble, shells, algae—and occasionally unsecured coral frags—and carry them around as camouflage.

So one morning you may discover that your expensive zoanthid frag has developed legs.

It probably hasn't.

Check the urchin.

Tuxedo urchins are generally considered reef-compatible, but they can graze coralline algae and their redecorating habit makes securely attached frags important. 

Best job: Rock and glass algae grazing
Cool factor: ★★★★★
Watch for: Loose frags, coralline algae and insufficient food

You may have dozens without realizing it.

Tiny brittle stars spend much of their lives tucked inside rockwork, beneath rubble and between coral structures, often extending only their thin arms into the water.

When food becomes available, those arms suddenly appear from seemingly every hole in the reef.

They're the aquarium equivalent of a cleaning crew working inside the walls.

Small reef-compatible brittle stars scavenge organic material in places that larger animals simply cannot reach and can become useful members of the live-rock community. 

Some can reproduce within aquaria, creating a self-sustaining population whose numbers respond, at least partly, to available resources.

Just don't assume every brittle star species behaves identically. Large species deserve their own research before being added.

Best job: Detritus and food trapped deep inside rockwork
Cool factor: ★★★★☆
Watch for: Correct species identification

A chiton looks as though someone crossed a mollusk with an armadillo.

Instead of the single shell found on most familiar snails, its back is protected by eight overlapping shell plates, allowing the animal to flex while remaining armoured.

Most aquarium-suitable herbivorous chitons slowly scrape microalgae, diatoms and biofilm from hard surfaces with a rasping feeding structure called a radula. 

They also grip rock extraordinarily well.

That creates one important rule:

Do not simply pull an attached chiton from the rock.

Their muscular foot creates an extremely strong attachment and forcibly removing one can injure the animal. 

There is another important distinction: most chitons encountered by reef keepers are harmless grazers, but not every chiton species has the same diet. Identification matters before intentionally adding an unfamiliar specimen. 

Best job: Biofilm, diatoms and encrusting algae
Cool factor: ★★★★★
Watch for: Species identification and improper handling

The next animals aren't necessarily appropriate for every reef.

But in the right aquarium, doing the right job, they can be extraordinary.

This may be one of the most fascinating ecological jobs occurring inside a mature reef aquarium.

Deposit-feeding sea cucumbers move across the substrate, ingesting sand containing bacteria, microalgae and organic material.

The material passes through the animal's digestive system.

Processed sand comes out the other end.

In other words, the animal spends much of its life literally eating the seafloor.

Species such as Florida sea cucumbers can function as generalist detritivores, processing organic material within the substrate. 

But this is not an animal to casually drop into a newly cycled aquarium.

Sand-feeding cucumbers need established systems containing enough natural food, and species selection matters considerably.

There is also a serious caveat.

Some sea cucumbers can release defensive toxins when severely stressed, injured or killed. 

Powerhead and overflow intakes should therefore be protected, and the exact species should be researched before purchase. 

Best job: Processing established sandbeds
Cool factor: ★★★★★
Difficulty: Advanced compared with ordinary snails
Watch for: Starvation, pumps, inappropriate tankmates and species-specific toxicity

Now we arrive at perhaps the most specialized member of the entire list.

Berghia stephanieae is not interested in your hair algae.

It doesn't care about leftover pellets.

It isn't going to vacuum your sand.

It wants Aiptasia.

That's essentially the job description.

Aquacultured Berghia are used in reef aquaria because they prey upon pest Aiptasia while leaving corals alone. 

They are small, delicate and largely nocturnal, which means you may add them and then wonder where your money went.

Give them time.

They can enter cracks where many other Aiptasia predators cannot.

There is, however, an unusual consequence of being such an extreme dietary specialist.

Once the Aiptasia disappears, so does their food supply.

The Berghia population will eventually decline unless the animals are moved to another aquarium containing Aiptasia. Passing them between local reef keepers can therefore be a wonderful example of biological pest management becoming a community resource. 

Best job: Aiptasia
Cool factor: ★★★★★+
Watch for: Wrasses and other predators—and eventually running out of Aiptasia

A serious outbreak of filamentous algae sometimes calls for something with a bigger appetite.

Enter the sea hare.

These bizarre mollusks look like someone designed a rabbit after only hearing a vague description of one.

But put the right sea hare into an aquarium full of suitable hair algae and it can be an impressive grazer. Modern reef-keeping guidance recognizes them as highly effective in the right situation. 

That effectiveness creates the problem.

Once the algae disappears...

what does the sea hare eat?

These are not animals I would add simply because they look interesting. They are better viewed as temporary specialists for systems capable of supporting their dietary needs, with a plan for supplemental feeding or relocation afterward.

Best job: Significant filamentous/hair algae problems
Cool factor: ★★★★★
Watch for: Starvation after the job is finished and species-specific husbandry requirements

This may be the most important lesson.

A clean-up crew should not be:

“I have a 100-gallon aquarium, therefore I need 100 cleaners.”

It should be:

“What ecological jobs does my aquarium actually need performed?”

Think in niches.

Problem                                                           Interesting candidate

Film algae in tiny crevices                             Stomatella snail

Dirty sand surface                                          Fighting conch

Tough algae on rock                                      Tuxedo urchin

Detritus deep inside rockwork                     Micro brittle stars

Biofilm and diatoms                                       Herbivorous chiton

Organic-rich mature sand                             Deposit-feeding sea cucumber

Aiptasia                                                             Berghia nudibranch

Major hair algae outbreak                             Appropriate sea hare 

And remember:

A clean-up crew does not remove nutrients from your aquarium simply by eating them.

Those nutrients are still moving through the ecosystem.

Good husbandry—appropriate feeding, mechanical filtration, nutrient management, water changes where appropriate and manual removal—remains essential. Your invertebrates complement those practices; they don't replace them. 

Perhaps there is a larger reef-keeping lesson hiding here.

Natural reefs aren't maintained by one organism doing everything.

Thousands of species occupy different niches.

One grazes.

Another scavenges.

Another turns over sediment.

Another consumes something that would otherwise dominate.

Together, they create balance.

Our aquariums become more interesting—and often more functional—when we begin thinking the same way.

So the next time you're choosing a clean-up crew, perhaps don't ask:

“How many snails do I need?”

Ask instead:

“What jobs need doing in this little ecosystem—and which animal evolved to do them?”
 

That is when a clean-up crew stops being a bag of invertebrates added after cycling.

It becomes part of the reef.

Which strange little reef animal deserves a place in the next Reefing Canada clean-up crew spotlight?

The ocean has been teaching these lessons for hundreds of millions of years. All we have to do is pay attention.
 

— Reefing Canada