The green shore crab, Carcinus maenas, known by many as an invasive species that can be found just about anywhere in the world, lives in the ever-changing environment of the estuaries. This common arthropod is able to tolerate changes in water salinity, fluctuations in water temperature and high concentrations of aquatic contaminants on a daily basis. However, researchers have now discovered that it can also do something else that is quite remarkable and was previously thought to be impossible: it can eat through its gills.

Tamzin Blewett, a post-doctoral fellow at University of Alberta, Canada, and her colleague Greg Goss found it strange that the largest group of estuarine inhabitants, the arthropods – which include crabs and other crustaceans – did not seem to tap into the protein-rich environment of the estuaries, while other species, such as soft-bodied invertebrates, some vertebrates and mussels, had been previously shown to take advantage of this protein-rich environment by absorbing nutrients through either their skin or their gills. This mechanism would seem to be impossible in the hard-bodied arthropods, whose gills hide behind a hard exoskeleton.

Undeterred by previous research that suggested that the crab gills are simply not suited for more than gas exchange and ion regulation, the two researchers developed a clever technique to investigate the ability of the green shore crab to take up the amino acid l-leucine, which is most prevalent in the estuaries and can be used as a source of protein in the body. The authors extracted sections of the front and rear of the gill, which are involved in gas exchange and ion regulation, respectively, from the crab. Then, they measured the rate of uptake of l-leucine by placing the gills in a carefully controlled solution consisting of artificial seawater and varying concentrations of l-leucine. Compiling their measurements, Blewett and Goss determined that l-leucine is indeed taken up via a specific transport mechanism at the gills.

When comparing l-leucine uptake rates between the front and rear portions of the gill, the duo found that the rear section of the gill, which is responsible for maintaining constant ion levels in the body, takes up more l-leucine than the front section and concluded that amino acid uptake may be linked to mechanisms that monitor and control ion levels in crabs. Perhaps these amino acids also play a role in maintaining a constant osmotic pressure in the arthropod bodies, to prevent unnecessary water uptake or loss in the ever-changing environment of the estuaries, where salinity varies daily. Although this still needs to be investigated, it is clear that this invasive, hardy crab uses all of its evolutionary advantages to thrive in one of the harshest environments on earth. In the words of the US kids show ‘Wild Kratts’, crabs have some ‘amazing creature powers’!

T. A.
G. G.
A novel pathway of nutrient absorption in crustaceans: branchial amino acid uptake in the green shore crab (Carcinus maenas)
Proc. R. Soc. B.
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