Testing   a   keystone   predator
   hypothesis.
<lI> The  sea  star Pisaster ochraceous feeds preferentially on mussels
but will consume other invertebrates.
<lI> When  Pisaster  was  removed  from  an  intertidal  zone,  mussels
eventually  took  over  the  rock  face  and eliminated most other
invertebrates and algae. In a control area from which Pisaster was
not removed, there was little change in species diversity.

   In  the absence of the sea star as a keystone predator, mussels become
   a dominant species in intertidal communities.

   Another  example  of  keystone species is the sea otter in kelp forest
   communities.