Ecology
Pycnopodia helianthoides is endemic but not limited to the shallow waters of the intertidal zone. It has been found in depths up to 450 meters and living on a variety of substrates, including mud, sand, and rocky bottoms. As the fastest of all sea stars, moving at a heart stopping rate of up to 160 cm/min, this quick and voracious carnivore feeds on snails, clams, scallops, hermit crabs, sea cucumbers, sand dollars, red, green, and purple sea urchins and sometimes abalone. It has also been seen scavenging subtidal filleted halibut carcasses.
Individual Sunflower Stars have a large range compared to other sea stars. They are commonly and abundantly distributed along the west coast of the United States from San Diego, CA to Unalaska, Aleutian Islands, AK Uniquely, this asteroid has a leading arm, which isn't distinctive physically. When turned in its aboral side the sea star will use the same arm or arms to right itself.
The Sunflower Star is well respected as a predator in the marine community, and many species have extreme defense responses to attack. The normally sluggish California sea cucumber will wiggle and the scallops will speedily swim away with valves tightly closed. Though it can evert its stomach to eke into the small openings between the shells of a bivalve, this sea star prefers to swallow its prey whole. Divers have reported seeing the spines of sea urchins sticking straight through the epidermis of its aboral surface. It is estimated that the Sunflower Star can consume up 44 sea urchins per year.