Probably the best herbivores for controlling algae in the reef aquarium are hermit crabs (see Shiemer, 1994). There are numerous small species that can be "put to work" in your aquarium to keep it free from problems with fast-growing algae. In order to maintain your hermit crab population be sure to provide a selection of empty shells for them to move into as they grow in size. Although we mention that these are herbivorous hermit crabs, they do eat other foods and will act as scavengers of uneaten fish food in the system. It is also important to note that the small (one inch. 2.5 cm) farm-raised tridacnid clams that are more frequently available to aquarists lately may be injured and killed by the otherwise harmless hermit crabs. The hermits first congregate on the clams' shells, eating attached filamentous algae. The presence of the hermit crabs on their shells stresses the clams, causing them to shut frequently. In time this weakens the clam to the point that it emits a stress-related strong smelling mucus, which really attracts the hermit crabs, and makes the situation much worse for the clam! When the clam emits this scented mucus the hermit crabs then begin to feed on its mantle tissue, and in a few hours there is no clam left, just a clean shell. It is safer to keep larger tridacnids with the hermit crabs, and small ones can also be kept with hermit crabs if they are fully acclimated and attached to a rock. Newly added, unattached small j clams are the most vulnerable to attack.
From the Caribbean, tropical Atlantic, Eastern Pacific and Hawaii we have several excellent species for use in the control of algae:
Paguristes cadenati. J. Sprung
Red-Leg (Scarlet) Hermit Crab Paguristes cadenati This bright red hermit crab has yellow eye stalks. It is found in the Caribbean almost exclusively on coral reefs. Rarely along rocky shores where other hermit crabs are common. It is most active at night. It usually stays on the rocks, but will sift through the substrate. This species is fond of red turf algae but will also feed on green hair algae. It grows to about one inch.
Red-Leg Hermit Calcinus tibicen
Bolder than the Red Hermit, as it will be active during the day. Grows to nearly two inches. It is found both on coral reefs and rocky shores in
- j the Caribbean, sometimes in large numbers. Tends to stay on the rocks. Eats turf algae, but also actively scavenges for uneaten food.
This species has a distinctive polka-dot red and white, greatly enlarged claw, and blue eyes. The legs are orange and the enlarged white claw looks like a snail's operculum when it draws into the shell. This species is also good at eating micro-algae in addition to turf algae, it will also eat coralline algae plates. Found on Caribbean coral reefs and occasionally along rocky shores. Never in large numbers. This is probably the most aggressive and active of the small hermits. They can literally run across the tank. Two specimens placed in the same aquarium may fight. Also sifts through the substrate. Grows to about one and a half inches.
Quite similar to the Polka-dotted Hermit in shape and behaviour. Found on coral reefs. Eats algae and actively seeks out all dropped food particles, but is safe with corals. Found on Caribbean reels, uncommon. Grows to about one inch.
Clibanarius tricolor; the "blue-leg" hermit crab is one of the best algae eaters for a reef aquarium. They stay small and move in packs to pick out filamentous algae from all of the nooks and crannies where snails can't reach. J. Sprung
Blue legs with red and white spots and black claws with white spots. Found in large aggregations in the sand or on rocks near shore in the Caribbean. Grows to about three-quarters of an inch. This is probably the best species for control of filamentous green "hair algae" and it is also effective for keeping the bottom substrate free of red slime algae (cyanobacteria).
This species with orange legs and a dark green body is found on rocky shores on the Pacific coast of Mexico, often in large aggregations. Grows to about one inch (2.5 cm).
Blue-Eye Hermit Paguristes sanguinimanus This hermit has an orange body and bright blue eyes. Occurs on sand flats and patch reefs in aggregations. Eastern Pacific. Good micro-algae eater. Grows to about half an inch.
Blue-Spotted Hermit Clibanarius digueti Reddish-brown legs with bluish spots. Found on rocky inshore substrates in the Eastern Pacific where it feeds on algae. Grows to only one-half inch.
This is a common crab along the shorelines of Hawai'i. It has an enlarged left claw, blue-eyes with orange eyestalks, brown legs
Calcinus laevimanus is a common intertidal hermit crab from Hawaii. It readily feeds on filamentous algae but should also be fed regular fish food. Photo taken at the Waikiki Aquarium. J. C. Delbeek with white tips and orange antennae. The are commonly found along intertidal shorelines and often use turban shells. They feed on filamentous algae and reach about one inch in length.
The Banded-Leg hermit crab Calcinus seurati Another common hermit crab along intertidal shorelines of Hawaii, it has blue eyes with bluish eyestalks, orange antennae and legs with white and black diagonal bands. Feeding of filamentous algae it grows to one-half and inch, and usually uses Nerite shells (pipipi in Hawaiian).
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