Pisaster ochraceus starfish-RS

Introduction
Starfish are invertebrates belonging to the echinoderm phylum and commonly live as long as twenty years, despite many sea stars living to a minimal age of four years. They, like other ectotherms, depend on external sources to regulate their body temperature. The starfish, ‘Pisaster ochraceus’, is a common starfish found in the Pacific Ocean and is considered an important indicator for the health of the intertidal zone. It is identified as a keystone species as it has a disproportionately large effect on its environment relative to its abundance.

Thermoregulation
When exposed to higher temperatures during a low tide, these sea stars increase their mass during the high tide by soaking up water from the sea. Following this hot low tide, the starfish fill their bodies with cold water during the next high tide, in preparation for the next low tide. This cold water acts as a protection from overheating in the sun.

If the temperature of the core of the starfish rises above 35˚C, its vital organs can’t function, causing it to die. However, in the heat, their arms become much warmer than their core, which indicates that it is likely that the arms act as heat sinks. This means that Pisaster ochraceus could have the ability to transfer heat from the core to the arms via fluid within themselves to regulate their temperature, which acts in a similar way to our circulatory systems. As a last resort, these starfish also lose one or more of their arms if they overheat for a long period of time, which acts as a survival and a thermoregulatory mechanism.