Interannual variations in vital rates of copepods and euphausiids during the RISE study 2004–2006

[1] The River Influences on Shelf Ecosystems (RISE) program investigated the role of the Columbia River plume in enhancing productivity in the upwelling zone off Washington during four cruises from 2004 to 2006. Measurements of growth rates and brood sizes of euphausiids and egg production rates of copepods were used as indices of secondary production to determine whether these rates differed (1) among cruises as a function of differences in upwelling strength and (2) with latitude, both within the RISE study area and between the coastal waters of Washington and Oregon. Euphausia pacifica growth rates were significantly higher during June 2006 than during July 2004 and June 2005 but not significantly different between the RISE study area and Newport Hydrographic (NH) Line, Oregon. Euphausiid brood sizes were significantly higher during August 2005 than during any other cruise for both E. pacifica and Thysanoessa spinifera; our experiments did not indicate that brood sizes were higher in the northern part of the RISE study region. E. pacifica broods were larger for NH than RISE, but T. spinifera broods were not. Significant differences in egg production rates (EPRs) were found among cruises for both Calanus pacificus and C. marshallae, with higher EPRs during August 2005. EPRs on other cruises were less than half the maximum rates known for these species. EPRs of C. marshallae were similar between RISE and NH; C. pacificus EPRs were significantly higher (lower) in the RISE region in 2005 (2006). Interannual differences in ocean conditions affected zooplankton production more strongly than differences in latitude.