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Wednesday, December 2, 2009

Thermoregulation of Sea Stars

Sea stars (also called starfish) are invertebrate animals belonging to the echinoderm phylum.  Although the larvae are free-swimming, as adults, these are slow-moving or sedentary marine animals that exhibit radial symmetry. Cold-blooded organisms (those that cannot maintain a consistent internal body temperature) with limited locomotion have to be able to adapt to different climactic conditions. This can be especially problematic for intertidal species that spend some time each day exposed to the sun. The sea star Pisaster ochraceus has found a novel way of coping with temperature fluctuations.

Sylvain Pincebourde of Fran├žois Rabelais University and his team observed the sea stars in controlled laboratory conditions. When the animals were exposed to higher temperatures during a simulated low tide, they increased their mass during the subsequent high tide. The sea stars had not been given any food, and so the increased mass had to come from soaking up water. The scientists found that following a hot low tide, the sea stars would fill their bodies with cold water during the next high tide, in preparation for the next low tide. When this second low tide hit, the sea stars were bulked up with cold water as a protection from overheating in the sun.

This is not to suggest that sea stars can remember events or plan strategies. It would be interesting to learn whether this type of thermoregulation is common among sedentary shoreline creatures.

Pisaster ochraceus, Ganges Harbour, Salt Spring Island, British Columbia, photo by Dr. Gordon E. Robertson.