Variability in northwards extension of warm water copepods in the NE Paci���c

The Continuous Plankton Recorder has been deployed in the NE Paci���c on two intersecting transects since 2000. Many deployments included a temperature sensor providing in situ temperature data to supplement the species abundance data for 1300 samples. Twenty-nine copepod taxa were suf���ciently abundant to examine their temperature-related distributions. Groups of warm- and cold-water species were identi���ed, with overlapping distributions between 48 and 588N. Recent ���uctuations in ocean climate, from the warmest year on record in 2005 to one of the coldest in decades in 2008, provided ideal conditions to observe temperature-related interannual variability. The abundance and northwards extension of warm water species were signi���cantly positively correlated with mean annual temperature and the Paci���c Decadal Oscillation. The cold water species showed no correlations with temperature/Paci���c Decadal Oscillation (PDO) within the study region; however, if the 4 years of sampling that extended south to 398N were examined separately, there was a strong relationship between temperature/PDO and the southern extent of subarctic copepods. Under warm ocean conditions, the range overlap of the two groups will increase as warm water species extend northwards, causing an increase in copepod diversity. Since warm water species are generally smaller and nutritionally poorer, this has implications for higher trophic levels