Zoster japonica (Dwarf Eelgrass; Japanese Eelgrass) typically grows in shallow water, (> 1 m depth, sometimes 3-7 m), and is often exposed to the air at low tide. It has a broad native range, from Vietnam to Kamchatka, and consists of warm-adapted and cold-adapted populations,. Leaves reach 200-250 mm, compared to 1,100 mm for the native Z. marina, which grows in the lower intertidal and subtidal. On the West Coast, it was first identified in 1975, in Padilla Bay, Washington, and now ranges from Kitimat, British Columbia to Humboldt Bay, the Eel River estuary, California. It may have been introduced in the 1950s, or earlier, with transplants of Pacific Oysters from Japan. Extensive mats of Z. japonica can reduce water flow over mudflats, reduce abundance of benthic invertebrates, and the abundance and condition of commercially important introduced clams (Mya arenaria, Ruditapes philipinarum). An eradication program for this seagrass was started in Humboldt Bay, but the results of this project are not known.