| Summary: | Rising seawater pCO2 (ocean acidification) presents a challenge for marine organisms. To counteract disturbances, many aquatic crustaceans excrete/accumulate acid-base equivalents through their gills; however, not much is known about the role of ammonia in this response. The present study investigated the effects of elevated pCO2 on acid-base and ammonia regulation in the Dungeness crab, Metacarcinus magister on the whole animal and the isolated gill level. Hemolymph pCO2 and [HCO3-] increased in M. magister acclimated to elevated pCO2 while pH remained stable. Additionally, hemolymph [Na+], [Ca2+], and [SO42-] were significantly increased. When challenged with varying pH during gill perfusion, the pH of the artificial hemolymph remained relatively unchanged. Overall, ammonia production and excretion were reduced in crabs acclimated to elevated pCO2, demonstrating that either amino acid metabolism is reduced in response to this particular stress, or nitrogenous wastes are excreted in an alternative form.
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