Purple Sea Star       Pisaster ochraceus



This mighty hunter of the intertidal and shallow subtidal zone can be seen almost anywhere hard substrate is found inside Puget Sound or on the open coast. Locally it is common on the piling at the Boston Harbor Marina. Whether clinging to piling or rocks, the Purple Sea star feeds on a variety of immobile or barely mobile prey animals from mussels to barnacles, even including shelled snails and chitons.


See video of Purple sea star.


The sea star uses its tube feet to move around and, when necessary, to cling tightly to the surface so it won't be washed away by waves or currents.  The tube feet are found along the bottom of each of it's five arms and in the middle surrounding its mouth.  The tube feet are also used in capturing mobile prey such as snails or prying open mussels or barnacles.  Once the prey shell is opened slightly the stomach is everted from the mouth into the prey where it digests the soft tissue leaving an empty shell.


The sea star has other unusual features. Look closely at its surface and you will find tiny pinchers which look like a parrot beak that are used to clean the surface of tiny organisms that may try to feed on it or attach to it. Even if you can't see the pinchers you can feel them. Put your forearm against the top of the seastar for several seconds and then pull it away.  The prickling sensation is your hair or skin being grabbed by the pinchers.


Another interesting feature is the small sacks protruding above the surface of the skin.  They are very thin providing contact between body fluids and the open water. This allows for the passage of oxygen from the water into the animal. They are found between the white dots on the back of the seastar in the photograph.


Finally note the small creamy white patch near the middle of the top of the animal. It is the sieve-like opening through which water is pumped to a water vascular system that operates the tube feet.


If you find these animals please only observe them and don't try to remove them.  They are a vital member of the local community. They are rarely eaten by other animals except the occasional seagull (It is quite a site to see a seagull with a small sea star part way down it's throat waiting for the partially swallowed legs to fold down so the rest of the animal can be swallowed).  However they are major predators on barnacles and mussels and their loss would allow an over-population of their prey reducing local community diversity.