Abstract
The occurrence of marine organisms northward of their known range limit along the eastern Pacific during El Nino Southern Oscillation (ENSO) events is an increasingly well-studied phenomenon. However, in addition to ENSO related range extensions, there are several mechanisms potentially contributing to the occurrence and persistence of extralimital populations. We report 12 new records of intertidal or shallow subtidal marine invertebrates (1 1 mollusks and 1 brittle star) along the southern and central coast of California. The 1997-98 ENSO event accounted for only one of these records, although previous ENSO events presumably contributed to the nine remaining northward records. Other mechanisms, such as thermal refugia and sampling artifacts, provide more likely explanations for nine of the northern and both of the southern new records.
