A novel pathway of nutrient absorption in crustaceans: branchial amino acid uptake in the green shore crab ( Carcinus maenas ).

Estuaries are environments enriched with dissolved nutrients such as amino acids. To date, marine arthropods are the only invertebrate group that have not been demonstrated to access this potentially important nutrient resource. Using in vitro gill perfusion techniques, we sought to investigate the ability of the green shore crab ( Carcinus maenas ) to take up the amino acid l-leucine directly from the water. Investigation of the concentration-dependent transport kinetics of radiolabelled l-leucine showed that there are two specific transport pathways across Carcinus gills, one with high affinity and low capacity, and the other with high capacity and low affinity. Using putative competitive substrates and reduced sodium preparations, we were able to identify the putative amino acid transport system associated with high-affinity uptake. This is the first study to demonstrate the absorption of dissolved organic nutrients across the gill epithelium of a marine arthropod.