Quantitative aspects of oxygen and carbon dioxide exchange through the lungs in Ocypode ceratophthalmus (Crustacea: Decapoda) during rest and exercise in water and air
AbstractGhost crabs Ocypode ceratophthalmus were exercised in air and water to measure CO2 and O2 exchange rates using the method of instantaneous measurements of oxygen consumption rate (MO2) where applicable. Average heart rate increased from 100 to nearly 400 pulses per minute after five minutes of exercise on a treadmill at a run rate of 0.133 m s-1. It took less than a minute for oxygen taken up through the lung epithelium from the air inside the branchial cavity to reach the maximal oxygen consumption rate of 26.1 mmol O2 kg-1 h-1. Resting MO2 was 4.06 mmol O2 kg-1 h-1 in air, but decreased to 3.37 mmol O2 kg-1 h-1 in seawater. Radioactive CO2 from injected l-lactate is released linearly by the lung. The percent accumulated 14-CO2 in exhaled air, plotted against time, intersects zero time on the x-axis, indicating rapid gas exchange at the lung surface. The P50 values for native haemocyanin of 4.89 mm Hg before exercise, and 8.99 mm Hg after exercise, are typical of a high-affinity haemocyanin usually associated with terrestrial crabs. The current notion that Ocypode ceratophthalmus drown when submerged in seawater was not substantiated by our experiments. MO2 in seawater increased from 3.37 mmol O2 kg-1 h-1 for resting crabs to 5.72 mmol O2 kg-1 h-1 during exercise. When submerged by wave-seawater in the natural environment and during exercise in respirometer-seawater O. ceratophthalmus do not swim but, having a specific density of 1.044, float nearly weightless with a minimum of body movements.
African Journal of Aquatic Science 2010, 35(1): 73–80