The physiological responses of the intertidal starfishPisaster ochraceuswere recorded during 6 h emersion in air
at temperatures of 5 °C, 15 °C or 25 °C, followed by a subsequent return to seawater (12–14 °C). After 6 h in 5 °C
air the body temperature of the starfish had equilibrated with the medium. In 15 °C and 25 °C air, evaporation
across the body surface prevented equilibration, and the body temperature remained several degrees cooler
than the air. In air, both oxygen consumption and CO2production increased with increasing temperature. The
oxygen consumption in air did not change when the body temperature of the starfish was similar to that of
seawater (11–13 °C), but appeared to be lower in the 25 °C air treatment. This suggests that the relationship
between oxygen consumption and water and air temperature is complex and both the magnitude of temperature
change, and the duration of aerial exposure may influence oxygen consumption. The low respiratory quotient
suggested that CO2excretion was not complete, possibly due to collapse of the tube feet and aboral papulae in
air. This leads to a temperature related increase in PCO2and a concomitant acidosis in 15 °C, and 25 °C air. In
5 °C air the PCO2of the coelomicfluid did not increase significantly and there was no change in pH, possibly
due to a temperature related pH increase. There was a slight increase in calcium ion levels in 15 °C and 25 °C
air and a drop in 5 °C air; in other species this represents a release of bicarbonate reserves from the exoskeleton,
however, no compensation of the acidosis was observed forP. ochraceus. It is likely therefore that this was a
passive dissolution of the exoskeleton caused by the acidosis, rather than an active compensatory mechanism.
Ammonia and lactate levels were very low or below detection threshold in most specimens which is typical
for echinoderms. The body temperature, gas levels and the pH of the coelomicfluid were rapidly regained
when the animals were re-immersed in seawater of 12–14 °C. Oxygen consumption remained higher during
the recovery period, possibly reflecting the up-regulation of processes associated with cellular repair. The results
of this study suggest that the physiological mechanisms reported here makeP. ochraceusideally suited for life in
the intertidal zone.
The physiological responses of the intertidal starfishPisaster ochraceuswere recorded during 6 h emersion in airat temperatures of 5 °C, 15 °C or 25 °C, followed by a subsequent return to seawater (12–14 °C). After 6 h in 5 °Cair the body temperature of the starfish had equilibrated with the medium. In 15 °C and 25 °C air, evaporationacross the body surface prevented equilibration, and the body temperature remained several degrees coolerthan the air. In air, both oxygen consumption and CO2production increased with increasing temperature. Theoxygen consumption in air did not change when the body temperature of the starfish was similar to that ofseawater (11–13 °C), but appeared to be lower in the 25 °C air treatment. This suggests that the relationshipbetween oxygen consumption and water and air temperature is complex and both the magnitude of temperaturechange, and the duration of aerial exposure may influence oxygen consumption. The low respiratory quotientsuggested that CO2excretion was not complete, possibly due to collapse of the tube feet and aboral papulae inair. This leads to a temperature related increase in PCO2and a concomitant acidosis in 15 °C, and 25 °C air. In5 °C air the PCO2of the coelomicfluid did not increase significantly and there was no change in pH, possiblydue to a temperature related pH increase. There was a slight increase in calcium ion levels in 15 °C and 25 °Cair and a drop in 5 °C air; in other species this represents a release of bicarbonate reserves from the exoskeleton,however, no compensation of the acidosis was observed forP. ochraceus. It is likely therefore that this was apassive dissolution of the exoskeleton caused by the acidosis, rather than an active compensatory mechanism.Ammonia and lactate levels were very low or below detection threshold in most specimens which is typicalfor echinoderms. The body temperature, gas levels and the pH of the coelomicfluid were rapidly regainedwhen the animals were re-immersed in seawater of 12–14 °C. Oxygen consumption remained higher duringthe recovery period, possibly reflecting the up-regulation of processes associated with cellular repair. The resultsof this study suggest that the physiological mechanisms reported here makeP. ochraceusideally suited for life inthe intertidal zone.
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