Your Guide to Marine Crustaceans
Marine crustaceans are the unsung heroes of every thriving saltwater aquarium. From the industrious hermit crabs patrolling your substrate to the elegant cleaner shrimp that literally pick parasites off your fish, these invertebrates fill critical ecological roles while adding personality and movement to your tank. If you think a reef is all about fish and coral, marine crustaceans will change your perspective entirely.
At ItsyBitsyPets, we cover marine crustacean care for hobbyists who want to understand these fascinating animals beyond just throwing a few hermit crabs into the tank and hoping for the best. The reef keeping community on r/ReefTank and Reef2Reef will tell you — a well-chosen clean-up crew of marine crustaceans can make or break a reef tank’s long-term health.
Popular Marine Crustaceans for Reef Tanks
The most commonly kept marine crustaceans fall into a few key groups. Hermit crabs — particularly blue-leg hermits, scarlet reef hermits, and Halloween hermits — are staple members of any clean-up crew. They scavenge uneaten food, graze on algae, and aerate the sand bed as they forage. Just make sure to provide extra empty shells in various sizes, because hermit crabs need to upgrade their housing as they grow and will sometimes evict snails if no spare shells are available.
Cleaner shrimp are another reef tank essential. Skunk cleaner shrimp (Lysmata amboinensis) set up “cleaning stations” where fish line up to have parasites and dead skin removed — a behavior you can observe daily in a home aquarium. Fire shrimp (Lysmata debelius), with their deep crimson bodies and white antennae, are among the most visually striking invertebrates in the hobby. Peppermint shrimp (Lysmata wurdemanni) earn their keep by eating pest aiptasia anemones that plague many reef tanks.
Marine Crabs for Your Aquarium
Beyond hermit crabs, several true crab species make excellent additions to reef aquariums. Emerald crabs (Mithraculus sculptus) are prized for eating bubble algae — a pest that few other clean-up crew members will touch. Porcelain crabs are tiny filter feeders that live commensally with anemones, waving their fan-like appendages to catch plankton from the water column. Arrow crabs have an alien appearance with their spindly legs and pointed snouts, and they help control bristle worm populations.
Not all crabs are reef-safe, though. Sally Lightfoot crabs can become opportunistic predators as they grow, snatching small fish and picking at coral. Decorator crabs will literally tear pieces off your prize corals to camouflage themselves. Research any crab species thoroughly before adding it to a reef tank — the LiveAquaria species profiles are a reliable resource for compatibility information.
Caring for Marine Crustaceans
Marine crustaceans share similar water quality needs with your saltwater fish — stable salinity at 1.025 specific gravity, zero ammonia and nitrite, and nitrate below 20 ppm. However, crustaceans are particularly sensitive to copper, which is commonly used to treat fish diseases. Even trace amounts of copper from old medications can be lethal to shrimp and crabs. Never medicate a display tank containing invertebrates — always use a separate quarantine tank for fish treatments.
Crustaceans also require adequate iodine levels in the water for successful molting. In a reef tank with regular water changes, iodine is typically replenished through the salt mix. In fish-only systems or tanks with infrequent water changes, supplemental iodine dosing may be necessary. A molting crustacean is extremely vulnerable — it will hide for a day or two while its new exoskeleton hardens, so do not panic if a shrimp or crab disappears temporarily.
Building Your Clean-Up Crew
A balanced clean-up crew combines multiple species that handle different types of waste and algae. A solid starting formula for a 50-gallon reef tank might include 10 to 15 hermit crabs of mixed species, one or two cleaner shrimp, an emerald crab for bubble algae, and a variety of snails for glass and rock grazing. Scale up or down proportionally for your tank size.
Avoid overstocking your clean-up crew. If there is not enough algae and detritus to sustain them, crustaceans will compete aggressively for food or start picking at coral and other invertebrates. Add your clean-up crew gradually as the tank matures and algae growth establishes. For more on building a complete marine ecosystem, check out our reef tank setup guide and explore the full range of saltwater pets available to hobbyists.