Sea stars can be important keystone species in marine ecosystems. They are efficient predators of prey that may otherwise dominate space, thus promoting species diversity. Yet, little is known on the ecological role of sea stars in southern Australia. This study aimed to understand whether Uniophora granifera could play a keystone role in temperate waters of South Australia. Abundance, size, feeding rate, and prey selection of U. granifera were investigated at two sites in Coffin Bay, which differed in habitat complexity. Underwater surveys were conducted through winter and spring. Abundance of U. granifera was highly variable and ranged from an average density of 10 to 63 individuals per 20 m2 across three surveys. Size ranged from 2 to 22 cm in diameter, average size was smaller (7.3 cm) at the site which included rocky substrate, compared to the seagrass/sand site (average size 15.4 cm). The diet comprised bivalves, gastropods, barnacles and amphipods, and reflected prey availability. Smaller sea stars consumed mainly barnacles, and at a higher feeding rate than larger U. granifera which preyed primarily on the mussel Brachidontes rostratus. Based on the main prey items, U. granifera has the potential to be a keystone predator, which invites further study.