EFFECTS OF ELEVATED-TEMPERATURES ON THE SCOPE FOR GROWTH AND RESISTANCE TO AIR EXPOSURE OF THE CLAM RUDITAPES-DECUSSATUS (L), FROM SOUTHERNPORTUGAL

The infaunal bivalve Ruditapes decussatus (L.) was collected from Ria Formosa, Fare, southern Portugal, and subjected to a range of selected temperatures (20-35 degrees C). Physiological measurements (clearance rate, respiration rate, excretion rate and absorption efficiency) for the calculation of scope-for-growth were under taken at 20, 27 and 32 degrees C after 48 hours acclimation. Experiments on tolerance to air exposure were performed at 20, 28 and 35 degrees C. Increasing temper ature resulted in lower clearance rates, leading to a marked reduction of scope for growth. At 32 degrees C scope for growth was negative in dicating that clams were having to utilize their energy reserves. Resp iration rate and excretion rate were temperature independent in the ra nge 20 - 32 degrees C; due to seasonal thermal acclimation to environm ental fluctuating temperatures. When exposed to air, shell valve gapin g was observed at all experimental temperatures, resulting in the util isation of aerobic metabolic pathways and the utilisation of energy re serves, desiccation and consequently death. Median lethal times were c a. 72 h, 48 h and 10 h at 20, 28 and 35 degrees C, respectively. Tempe ratures above 28 degrees C can therefore significantly weaken clams re sistance to air exposure and affect their performance in water. Even i i effects of exposure to high water and air temperatures, on the tidal flats in the summer, are unknown, raising temperatures constitute a s ignificant physiological stress for the clams.