SEASONAL RESTING METABOLIC RATE IN PLATORCHESTIA PLATENSIS (AMPHIPODA, TALITRIDAE)

Populations of Platorchestia platensis were collected throughout the annual season at Indian Point (N.B., Canada), then acclimated (wrack or driftwood) and oxygen uptake measurements were made on individuals at standard temperature (approx. 19 degrees C) and lighting conditions (12: 12-hour light: dark). P. platensis reduces resting rate (= standard metabolic rate, SMR) and growth and reproduction cease (diapause) during the colder months. SMR and growth begin increasing when the warm season starts towards the end of March at Indian Point. Wrack-acclimated P. platensis SMR peaks near the summer solstice in June and a month later for driftwood-acclimated populations. The SMR of wrack-acclimated P. platensis at 45 degrees N begins dropping, following the June peak, towards a period of overwintering dormancy (= diapause) to be reached near the vernal equinox in September. Wrack-acclimated populations of P. platensis in winter maintain their inverse metabolic relationship with size. During winter in driftwood-acclimated populations, the relationship with weight is lost.