Temperature-dependent consumption and gut-residence time in the opossum shrimp Mysis relicta

Maximum daily consumption was estimated for Mysis relicta fed ad libitum rations of Daphnia pulex at 4,10,15 and 18°C. Gut-residence time was also evaluated for M.relicta fed clado-ceran prey at 4, 10 and 157deg;C. Mean daily consumption (g dry weight of Daphnia g −1 dry weight of Mysis day −1 ) ranged from 6% at 4%C to 12% at 10°. At 18°C, Mysis feeding rate declined to 9% day1. Mean, weight-adjusted consumption rates exhibited a ‘dome-shaped’ response in relation to water temperature. Consumption rate was highest at 10°C and lowest at 4°C. Estimated Q10 was more sensitive from 4 to 10°C ( Q10 = 3) than from 10 to 15°C ( Q10 =1.2). Gut-residence time for Mysis was inversely related to water temperature, implying that evacuation rate increases linearly with water temperature. Feeding and gut-evacuation rates become disassociated at water temperatures >10°C. As water temperature increased above 1°C, relative evacuation rate increased, whereas feeding rate declined. It is postulated that at higher water temperatures, disassociated feeding and gut-evacuation rates reduce the scope for growth of vertically migrating Mysis and impose a physiological constraint that isolates Mysis from warm, epilimnetic water during thermal stratification.