Impact of Changing Temperature on Critical Thermal Maximum and Metabolic Rate of Uca perplexa and Uca crassipes

This study quantifies thermal tolerance and metabolic rates for two fiddler crab species ( Uca perplexa and Uca crassipes ) exposed to increasing temperatures. Uca perplexa prefers sun-exposed mangal zones, while U. crassipes inhabits shaded as well as sun-exposed areas. A total forty crabs (20 crabs from each species) were collected from the Ambeua mangrove on Kaledupa Island, and transported to the Hoga Island Research Laboratory for testing. Fifteen crabs of each species were used for CTmax trials, and five crabs were used in metabolic trials. Crabs were acclimated for 10 days at 26, 28, or 30°C prior to experimentation. Critical Thermal Maximum (CTmax) was measured by increasing the temperature by 0.3°C per minute until loss of righting responses was observed. A Gilson differential respirometer was used to determine oxygen uptake at 26 and 31°C for each species, and the results used to calculate temperature quotient (Q 10 ) values. While both crab species showed an increase in thermal tolerance with increasing acclimation temperature, U. crassipes was more heat tolerant (CTmax = 42.21°C), than U. perplexa (CTmax = 41.95°C). Likewise, U. crassipes was less metabolically sensitive to temperature increase (Q 10 = 1.33) than U. perplexa , (Q 10 = 2.38) suggesting that U. crassipes is better adapted to high environmental temperature conditions.