Nitrogen excretin in crustacea–I. The herbivorous land crab Cardisoma guanhumi latreille

Abstract

1. 1. The large land crab, Cardisoma guanhumi, does not alter its pattern of nitrogen excretion with dehydration. 2. 2. Although generally ammonotelic, crabs on a relatively high nitrogen diet have high levels of blood urea (18 mg per cent), which is subsequently excreted via urine. The high urea levels are especially conspicuous 24–48 hr after a meal. In contrast, on a low nitrogen diet blood urea levels are hardly detectable. Interpretation of data on total nitrogen excretion is further complicated by the presence of large deposits of uric acid in the hemocoel. 3. 3. Total nitrogen excretion is low (2.05 mg N/100 g per day) and may be correlated with the crab's herbivorous and terrestrial nature. For these herbivores that are naturally on a low nitrogen diet, low levels of nitrogen excretion and uric acid deposition apparently suffice for the disposal of nitrogen from amino acid catabolism. 4. 4. Gill-associated urease activity is discussed in relation to its influence on crustacean nitrogen excretion.