Short answer: It depends, and it varies by the type. “Starfish” isn’t a very specific term, after all.
Taking extremes, some cannot survive any significant exposure to air; even a few seconds is lethal—crown-of-thorns can easily rupture on exposure to air and leak all their body fluids out rapidly. Others, such as ochre stars (a common species on the Pacific Northwest coast of North America) pump themselves full of seawater and then cling tightly to a rock with their hydrostatic tube-feet, retaining water as a heat sink and simply waiting out the high tide. Even species that aren’t especially resilient to air exposure may take days to fully die, despite having undergone lethal exposure.
Short answer: It depends, and it varies by the type. “Starfish” isn’t a very specific term, after all.
Taking extremes, some cannot survive any significant exposure to air; even a few seconds is lethal—crown-of-thorns can easily rupture on exposure to air and leak all their body fluids out rapidly. Others, such as ochre stars (a common species on the Pacific Northwest coast of North America) pump themselves full of seawater and then cling tightly to a rock with their hydrostatic tube-feet, retaining water as a heat sink and simply waiting out the high tide. Even species that aren’t especially resilient to air exposure may take days to fully die, despite having undergone lethal exposure.
Thanks!