Rocas Alijos lies 180 nautical miles west of Baja California. It comprises several exposed rocks that surmount a large oceanic volcano rising from the ocean floor well off the continental shelf. It is located at the transition zone between two major biologic provinces, at a latitude where the Pacific Current turns westward to form the north Pacific trans-oceanic current. In spite of its obvious importance for biogeographical studies, the remoteness of Rocas Alijos and its small size thwarted any major scientific work until very recently, and the topography, biota, and oceanographic conditions...