The Western Sea Slater (Ligia occidentalis) is an isopod closely related to pillbugs, typically 15–25 mm long with a flattened, gray-to-brown body and long, sweeping antennae. They range along the Pacific coast from British Columbia to Baja California, and here in the Bay Area they occupy the splash zone just above the high tide line, tucking into rocky crevices and algal mats by day and emerging at night or in foggy conditions to feed on decaying algae and organic debris. As detritivores, they play a key role in breaking down material along the shoreline, and their presence is often used by researchers as an indicator of rocky intertidal ecosystem health.
Photo credit: Eric Bing