Jonathon H. Stillman, a marine biologist at Stanford University, tested the heat tolerance of four species of crabs found in the shallow waters of the Pacific Ocean. Two of the crab species were from the Oregon coast and lived in waters that range from 47 degrees to 59 degrees in temperature. The other two came from the Gulf of California in Mexico and thrive in waters of 54 degrees to 86 degrees. Live specimens of the animals were placed in aquariums ( 鱼缸 ) which were held at a constant temperature just at the upper thermal range of their natural habitat. The crabs were then outfitted with sensors that measured heart beat. The temperatures were raised in the individual aquariums by about a fifth of a degree a minute until the animals’ heart beat stopped. This established the upper thermal tolerance limit for each of the species. The Mexican crabs that lived in the hottest climate were the least able to adapt to an increase in temperatures above that which they normally encounter in their natural home. Temperatures in the habitat of one of the crabs often reaches 105.8 degrees F, but the animals died at 106.2, less than a degree above normal. One of the Oregon species was acclimated to a temperature of 65, but survived until the aquarium temperature reached 87. The crabs that came from the Oregon coast adapted best to a rise in temperature and had the greatest capacity to increase their heat tolerance.