CUC (Clean Up Crew)
The set of scavenger invertebrates that keep a marine aquarium clean: snails, hermit crabs, crabs, starfish, urchins, shrimps.
Detailed explanation
The Clean Up Crew is the biological maintenance team of a marine aquarium. Each member has a specific role in the cleaning chain.
The snails Trochus and Astrea scrape algae from glass and rocks. Nassarius scour the sand for debris and food. Cerithiums do the same on rocks. Stomatella snails are small and very discreet, excellent biofilm eaters.
Hermit hermit crabs (Clibanarius, Calcinus) are opportunistic omnivores. They eat algae, debris, leftover food. The blue-legged hermit crab (Calcinus elegans) is the most popular. Be careful: hermit crabs can kill snails to steal their shells. Better to have empty shells available.
Crabs should be chosen with caution. Porcellanid crabs and emerald crabs (Mithraculus sculptus) are reef safe and eat bubble algae (Valonia). Many other crabs are opportunistic predators that attack coral and fish at night.
Serpentine stars (Ophiuridae) are excellent nocturnal scavengers. They crawl between rocks and collect debris. The micro-serpentines that come with the live rock are precious.
Urchins (Diadema, Echinometra) are the best algae eaters of coral and filamentous algae but can damage corals with their spines and displace fragments.
Lysmata shrimp complete the team by cleaning fish from parasites.
The recommended quantity depends on the volume. A rough rule of thumb is 1 snail per 5 litres, 1 hermit crab per 10 litres, a few shrimp and serpentine stars. Don't overdo it: too many scavengers in a clean aquarium die of starvation.