EPOW - Ecology Picture of the Week

Cushion Star of the Southern Seas

Cushion Star (Patiriella regularis), Family Asterinidae
Takaka, New Zealand

Explanation:   Washed up along this dark-sand beach in southern New Zealand is a radially-symmetrical predator of the intertidal ecosystem -- a cushion star (more erroneously called a starfish, although it is not a fish ... and, strictly speaking, not a star either ...).

Cushion stars seem to vary in color and genetics along their range of North and South Islands in New Zealand.  The variation in colors may have arisen from isolation of local populations caused by geographic barriers to dispersal of larvae such as the upwelling zones south of Cook Strait.  Whether the colors have local adaptive significance apparently is unstudied.  The usual colors are grayish-green and dark blue, but less commonly orange, purple, and -- in this week's photo -- yellow forms also occur.     

Cushion stars are the most common star found throughout New Zealand, and can grow to 100 mm (4 inches) across.