Starfish are capable of regulating their body temperature by pumping itself up with cold seawater, according to research published in a recent issue of the journal American Naturalist.
The study by Sylvain Pincebourde, Eric Sanford, and Brian Helmuth studied the ochre sea star (Pisaster ochraceus), a common inhabitant of rocky intertidal communities along the Pacific Coast of North America.
The sea star is exposed to air during low tide and cannot move until the tide comes back in and submerges it. In the presence of a warm sun, this can potentially lead to heat stress.
Pincebourde and colleagues carried out a series of experiments in which they measured the wet body mass of the sea stars held in aquaria during simulated high and low tides while exposing them to different regimes of heat.
The wet body mass was used as a proxy for the mass of coelomic fluid, which is largely composed of seawater, in the sea stars. The sea stars were not fed during the period of the experiment (to prevent the mass of the food items from confounding the results).
The authors found that the sea stars exposed to higher temperatures showed an increase in wet body mass.
This implied that the volume of coelomic fluid was greater in these sea stars and that the sea stars were modulating their body temperatures by imbibing greater amounts of cooler-than-air seawater into the coelom (a fluid-filled cavity).
This method of thermoregulation was found to be surprisingly effective, being able to lower the temperature of the sea stars by as much as 4C.
The authors conclude, Thermoregulation in P. ochraceus is more effective after exposure to cold seawater, and the probability of experiencing high aerial body temperatures increases when sea temperature is elevated. When placed in a global change context, these results suggest that a continued increase in ocean temperature may compromise the ability of sea stars to avoid thermal stress during aerial exposure at low tide.
For more information, see the paper: Pincebourde, S, E Sanford and B Helmuth (2009) An intertidal sea star adjusts thermal inertia to avoid extreme body temperatures. American Naturalist 174, pp. 890"897.