Abstract
At low tide, the green crab, which is capable of breathing air, may leave the water and walk on the foreshore, carrying branchial chamber fluid (BCF). N-waste metabolism was examined in crabs at rest in seawater (32 ppt, 13°C), and during 18-h recovery in seawater after 1 h of exhaustive exercise (0.25 BL s-1 ) on a treadmill in air (20°C-23°C), or 1 h of quiet emersion in air. Measurements were made in parallel to O2 consumption (ṀO2 ), acid-base, cardio-respiratory, and ion data reported previously. At rest, the ammonia-N excretion rate (ṀAmm = 44 µmol-N kg-1 h-1 ) and ammonia quotient (AQ; ṀAmm /ṀO2 = 0.088) were low for a carnivore. Immediately after exercise and return to seawater, ṀAmm increased by 65-fold above control rates. After emersion alone and return to seawater, ṀAmm increased by 17-fold. These ammonia-N bursts were greater, but transient relative to longer-lasting elevations in ṀO2 , resulting in temporal disturbances of AQ. Intermittent excretion of urea-N and urate-N at rest and during recovery indicated the metabolic importance of these N-wastes. Hemolymph glutamate, glutamine, and PNH3 did not change. Hemolymph ammonia-N, urea-N, and urate-N concentrations increased after exercise and more moderately after emersion, with urate-N exhibiting the largest absolute increments, and urea-N the longest-lasting elevations. All three N-wastes were present in the BCF, with ammonia-N and PNH3 far above hemolymph levels even at rest. BCF volume declined by 34% postemersion and 77% postexercise, with little change in osmolality but large increases in ammonia-N concentrations. Neither rapid flushing of stored BCF nor clearance of hemolymph ammonia-N could explain the surges in ṀAmm after return to seawater.
Published Version
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