Physiological responses to hypoxia and anoxia in Jehlius cirratus (Darwin,1854) (Cirripedia, Chthamalidae) in the upper intertidal zone

The physiological capacities of the chthamaloid cirripede Jehlius cirratus were evaluated under hypoxic and anoxic conditions. J. cirratus is the domi nant species in the upper intertidal zone (3-6.5 m above the lowest tidal l evel) in southern Chile; local tidal amplitudes of 7 m on the average produ ce cyclic periods of food scarcity and long periods of hypoxia and anoxia, involving survival risk. J. cirratus demonstrated a high capacity for aerial respiration, with no di fference between periods of emersion of 1 h and 3 h, but differing at diffe rent temperatures: it was higher at 20 degreesC than at 10 degreesC. Aerial respiration capacity ranged between 74.5% and 89.5% of total respiration i n submersion. No significant oxygen debt was observed after maintaining the specimens in emersion for 3 h and 6 h. J. cirratus had a high survival rate in emersion at 16 degreesC (LP50 = 25. 0 days +/- 4.5) and in anoxic submersion (LP50 = 8.4 days +/- 3.8) and a hi gh tolerance to desiccation, with low rates of water loss during prolonged emersion, even under high temperature conditions. These results show that J. cirratus possesses a high capacity for adaptatio n to emersion and desiccation. This explains their dominance in the upper i ntertidal zone in southern Chile, where there are large variations between tides.