How do decapods breathe in water and on land?

Decapods, a group of crustaceans that includes crabs, shrimp, and crayfish, primarily utilize gills for gas exchange. These gills are typically vascularized outgrowths located within a branchial chamber beneath the carapace, where specialized appendages create respiratory currents to move water over the respiratory surfaces.12

For species that transition to land, respiration involves specific adaptations to manage the challenges of air-breathing:

• Branchial Chambers: Land crabs possess larger, more highly vascularized branchial chambers compared to their aquatic counterparts.2
• Moisture Retention: To prevent the gills from drying out, land crabs have evolved specialized chambers designed to keep the respiratory surfaces moist, which is essential for gas diffusion.2
• Metabolic Adjustments: While aquatic crustaceans often rely on high ventilation rates, some species, such as the square-backed crab (Sesarma), may reduce their activity and oxidative metabolism when oxygen levels are low or conditions are unfavorable.1

Overall, gas exchange in decapods relies on the diffusion of gases across these respiratory surfaces, often supported by respiratory pigments like hemocyanin in the blood.2