Abstract
This lab accompanies a lecture about comparative animal cell and systems physiology. Fiddler crabs (Uca pugnax) are collected during a field trip to mudflats of Arthur Kill between Staten Island and New Jersey. However, other euryhaline animals could replace the fiddler crabs. Students are responsible for the animal care throughout the semester. The crabs are acclimated to waters of 3 different salinities (30, 20 and 10 ‰). Students use simple approaches to determine the osmotic concentrations in the external media and in the animals' hemolymph to reveal the osmotic gradients maintained by the crabs. Passive salt loss is estimated from the conductivity increase of a volume of distilled water after inserting 1‐2 crabs, allowing to estimate the energy needed to maintain the osmotic gradient. Finally, the metabolic rate of the crabs in the different waters is measured and compared to the theoretical expectation on the basis of different assumptions about the metabolism of the crabs. At the end of the course, the animals are returned to their natural habitat.
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