An assessment of seasonal adaptation in the beach hopper Talorchestia quoyana (Milne-Edwards)

Abstract

Summer and winter oxygen consumption of the beach hopper Talorchestia quoyana (Milne-Edwards) was measured in air and following submersion at temperatures between 5 and 30°C. In all experiments, oxygen consumption increased with dry body weight; the weight exponent being similar in air and seawater. There was no change in the respiratory rate-temperature curve in summer and winter samples. At exposure temperatures > 10°C, aquatic rates were relatively independent of temperature and less than the aerial rates which were markedly temperature dependent. Following laboratory storage at 5 and 20°C (approximating winter and summer field temperatures), aerial oxygen uptake was similar in the two treatments at temperatures between 5 and 30°C. LT 50 values for small, medium and large Talorchestia submerged in salinities between 0.3 and 68%. S showed mortality increased with size, temperature and at extreme salinities. At optimal salinities (34 and 17%. S) during winter, amphipods of all size groups showed increased resistance to submergence at exposure temperatures < 15°C. Small amphipods exposed to a cyclic temperature regime between 5 and 15°C showed increased survival compared with upper and lower constant temperatures. The respiratory patterns and salinity adaptation were related to the habitat characteristics of juvenile and adult Talorchestia. The lack of seasonal adjustment in aerial oxygen uptake in Talorchestia may be an important adaptation in maintaining activity and other behavioural patterns during winter.