Antarctic intertidal limpet ecophysiology: a winter-summer comparison

The Antarctic intertidal zone is one of the world's most extreme marine environments. As well as having a typically high annual temperature variation (~ 30 °C), it is affected by frequent ice scouring in summer and ice encasement in winter, as well as substantial salinity fluctuations during tidal cycles. For many years the Antarctic intertidal was believed to host only migratory species during summer, however, recent studies have found several permanently resident macrofaunal species, including the limpet Nacella concinna. Here we present results of the first seasonal comparison of different ecophysiological parameters in this species collected from the intertidal in both winter (August and September) and summer (January and February) on Adelaide Island (West Antarctic Peninsula). There was clear evidence of seasonal acclimatisation with a shift in thermal window between winter and summer limpets. The seasonal change in metabolic rate did not show increased costs in winter (cf metabolic cold adaptation) and the seasonal increase in oxygen consumption was within the range expected due to the physical effects of temperature alone. O:N ratios indicated that the animals were using the same metabolic substrate (mainly protein) all year round. There was no significant difference in condition factor between winter and early summer individuals. However comparisons with subtidal N. concinna showed that those from the intertidal had a lower condition factor than those permanently immersed. Whilst remaining in the ice-encased intertidal during winter may give access to ice-algae and microphytobenthos in the shallows and provide a feeding advantage early in the season, there are clearly extra costs to living in the intertidal per se. Hence N. concinna may not derive any obvious fitness advantage but may simply be occupying an available niche and surviving the physical challenges in the shallows.

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