In the July issue of Ecology Letters, Paine and Trimble describe a dramatic assemblage shift on a rocky intertidal shore in Washington State (USA). The change was initiated during the extreme 1997/98 El Niño and has involved replacement of the original algal dominated assemblage by a mussel bed.
Starfish are capable of controlling the distribution and abundance of these mussels. The authors argue for two possible outcomes: gradual recovery of the algal assemblage as the mussels are consumed, or formation of a persistent alternative state if the mussels grow to a sufficient size to escape further predation.
The study emphasizes the ecological importance and generality of size escapes, a mechanism also characterizing potentially permanent transformations of terrestrial grasslands to forests.