Larval dynamics of the sand crab, Emerita analoga, off the central Oregon coast during a strong El Nino period

Populations of the sand crab, Emerita analoga, are well established on the California coast. However, populations in Oregon occur sporadically and appear to be restocked by larvae drifting north from California. Due to increased northward transport in winter during El Nino events, we would expect that larval recruitment to northern populations should be higher during these periods. This hypothesis was tested by comparing larval abundances between non-El Nino and El Nino years, 1997 and 1998, respectively. In 1997, larval abundances and seasonality were similar to historical data from 1969-71. First zoeal (Z1) stage larvae were present during these summers, but in low numbers, indicating th at E. analoga spawned off the coast of Oregon. In 1998, strong larval recruitment from the south occurred, demonstrated by a large number of fifth zoeal stage (Z5) larvae collected off Oregon in April and May. The large numbers of Z1 found in summer 1998 indicate that the Z5, which arrived from, California earlier that spring, successfully recruited to adulthood and reproduced. These data indicate that Oregon E.analoga populations are probably dependent on larvae travelling from California in the Davidson Current. It follows that this species could be used as an indicator of coastal current fluctuations such as those seen during El Nino events.