Scarlet Reef Hermit Crab

Paguristes cadenati

Saltwater Invertebrate Species Group: Crab Family: Diogenidae

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Water parameters

Temp 76-80 F Temperature

Maintaining a stable and appropriate temperature is critical for the survival of aquatic life.

pH 7.8 - 8.4 potential of Hydrogen

Measuring the acidity or alkalinity of water on a 0–14 scale, where 7 is neutral, 7 is alkaline.

NO3 1-20 ppm Nitrate

While less toxic than ammonia, high nitrate levels (above 40–80 ppm) are important to monitor because they can cause fish stress, stunted growth, and harmful algae blooms.

NO2 <0.0001 ppm Nitrite

It is a highly toxic, intermediate compound in the nitrogen cycle produced from broken-down ammonia

PO4 0.01 - 0.1 ppm Phosphate

It is essential for plant development but must be managed, as excess levels trigger nuisance algae blooms and inhibit coral calcification.

NH3 <0.1 ppm Ammonia

It is the primary killer of aquarium fish, causing gill damage, stress, and death

Ca 380 - 450 ppm Calcium

Supporting the growth, skeletal structure, and shell formation of corals, mollusks, crustaceans, and coralline algae

KH 8 - 12 dKH Alkalinity

It acts as a shield, neutralizing acids to prevent dangerous pH "crashes" that can harm fish, corals, and plants.

Mg 1200 - 1400 ppm Magnesium

It enables coral growth by supporting skeletal formation, assists in metabolic processes, and ensures that calcium is available for corals, clams, and coralline algae.

SG 1.023 - 1.026 SG Salinity

Essential for maintaining stable, natural water parameters, proper osmoregulation, and stress-free environments for marine fish and corals

ORP 250 - 400 mV Oxidation-Reduction Potential

A higher positive mV indicates clean, oxygen-rich water with high water quality, while low readings indicate high pollution.

About Scarlet Reef Hermit Crab

General information

Paguristes cadenati is very hardy and requires minimal care in a well-established system. More importantly, however, these small hermit crabs have a voracious appetite for detritus and algae. In fact, they are particularly fond of nuisance algae of the filamentous, hair, and slime varieties, as well as cyanobacteria. Finally, unlike some hermit crabs, most Scarlet Reef Hermit Crabs are very peaceful towards their tankmates. The Scarlet Reef Hermit Crab is named for its bright red legs, which are contrasted by their yellow face. Native to the reef faces and coral rubble of the Caribbean and Western Atlantic, these active scavengers can consume large amounts of animal matter and algae. Despite their large appetites and constant feeding habits, the Scarlet Reef only grows to an adult size of 1-1/2″” in length. Like other hermit crabs, an ample supply of empty shells should be available for the Scarlet Reef Hermit Crab to move into as they molt and grow. As with all invertebrates, they do not tolerate copper-based medications and extreme fluctuations in water parameters. Also, take special care to ensure an invertebrate-friendly environment free of predators.

Diet & nutrition

The diet of Scarlet Reef Hermit Crab is mainly detritus and algae. It is also fond of filamentous, hairy, and slimy nuisance algae and cyanobacteria.

It is considered to be one of the reef safe hermit crabs that can be added in an aquarium. It is best kept in a reef system with adequate supply of algae since they eat almost anything. In areas with low algae supply, the scarlet reef hermit crab eats dried seaweed and other marine food.

Determining sex

Female scarlet reef hermit crabs can be distinguished from the males because of the presence of two tiny genital openings called gonopores. These are situated at the back of her legs, near the abdomen and the joint of the cephalothorax. Males do not have this characteristic.

Females have egg pouches; males do not.

Females also have little hair on their bodies compared to males.

Breeding & spawning

Sexual reproduction among female and male scarlet reef hermit crabs happens when they pull themselves out of their shells, and their midsections meet for a few minutes. Eggs are carried by the female crab until they are ready to be hatched. The young hermits will then be released while the lights are off.

However, breeding in the aquarium is extremely difficult.

Origination

Scarlet reef hermit crabs are native to the reef faces and coral rubble of the Caribbean and Western Atlantic.

Cautions

Almost every saltwater crab is sensitive to copper traces in the water so copper treatments should not be used in tanks with hermit crabs. They are also very sensitive to extreme fluctuations in water parameters.

Acclimation process

When taking the invertebrate out, expose it to as little light as possible and turn the aquarium lights off. Place the invertebrate container bag in the aquarium and let it float for 15 minutes. Open the bag and pour in 1 ounce of aquarium water into it, do so every 5 minutes until the water inside the bag has doubled. Wait for 5 minutes before pouring off half the water inside the bag into the aquarium. Then, slowly place each animal in the aquarium. Turn the aquarium lights on after an hour or more.

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