Santa Monica city councilman Richard Bloom was sworn in today as the south coast representative on the California Coastal Commission, succeeding Larry Clark of Rancho Palos Verdes. More than a dozen other Southern California representatives in two counties had been angling for the slot, which is filled by the state Senate Rules Committee. Bloom, appointed yesterday, had the backing of several environmental groups. With Bloom quickly seated, I'm hearing that Wiliam Burke lost a bid to remain vice chairman of the commission at today's meeting in San Francisco, with Mary Shallenberger of San Francisco getting the post.