Results of a 50yr study on population changes in ochre stars Pisaster ochraceus in Monterey Bay, California are presented by a consortium of west-coast researchers.  The study focuses on 3 sites, one dominated by mussels Mytilus californianus and the other sites being relatively mussel-poor.  Major observations are: 1) sea-stars are much smaller now at the mussel-dominated site, but in greater abundance, and 2) the reverse is true at the other 2 sites.  In fact, in 2005 only a few relatively large individuals are seen at these last sites.  The authors speculate on causes of these changes, such as the possibility of size-selective predation by sea otters at the first site, but are unclear on what factors may have been involved at the other 2 sites.  Pearse et al. 2010 p. 633 In, Echinoderms: Durham (Harris et al., eds) Taylor & Francis Group, London.

Ochre stars Pisaster ochraceus forage
in a mussel bed at low tide 0.25X