Some Aleutian Islands are surrounded by urchin barrens while others are surrounded by kelp forests. Which statement gives the primary explanation for these differences?

A) Kelp forest islands and urchin barren islands differ with respect to oceanic currents.
B) Kelp eat urchins, thus preventing their establishment.
C) The kelp forest islands experience a substantially warmer climate than do the urchin barren islands.
D) Grazing by urchins prevents the formation of kelp forests.