Rapid shift in zooplankton community composition on the northeast Pacific shelf during the 1998–1999 El Niño – La Niña event

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Zamon, Jeannette E, Welch, David W
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2005
• Subjects: Aquatic Science; Ecology, Evolution, Behavior and Systematics; Pacific; Alaska; Copepods
• Online Access: http://dx.doi.org/10.1139/f04-171; http://www.nrcresearchpress.com/doi/pdf/10.1139/f04-171

The 1997–1998 El Niño was one of the strongest ocean warming events in the historical record followed by an equally strong cold La Niña event in 1999. We observed a rapid shift in the marine zooplankton assemblage found in the transitional area between the California Current domain and the Alaska Gyre domain. Nonmetric multidimensional scaling revealed that the shift in species composition was caused primarily by changes in the relative abundance of subtropical neritic copepods normally found in the California Current domain. In 1998, the subtropical neritic copepods Paracalanus, Ctenocalanus, and Corycaeus were found as far north as 56°N and occurred in 100%, 96%, and 51% of 1998 samples versus 16%, 5%, and 3% of 1999 samples. The type and magnitude of change were similar to those observed off central Oregon but differed from those observed in southeast Alaska. Results support the hypothesis that anomalous poleward transport can inject significant California Current water into the coastal circulation of the Alaska Gyre and suggest that alongshore connectivity between the two domains may extend farther to the north than previously thought.