Zooplankton community composition along the inner portion of Line P during the 1997–1998 El Niño event

The 1996–1999 zooplankton samples from oceanic waters off southern British Columbia provide time series descriptions of biomass and community composition before, during, and immediately after the 1997–1998 El Niño event. Our most frequent sampling (every month in 1998 and three to four times per year in other years) was off southern Vancouver Island, and extended seaward from the shelf-break to approximately 200 km offshore along and adjacent to the inner third of the long-term Line P/Station P section (48°30′–49°N, 126–130°40′W). El Niño-associated changes in the zooplankton community were most apparent over the shelf-break and slope, and weaker further offshore. At the nearshore portion of this line (P03–P06), the 1997–1998 differences from long-term seasonal averages included both lower total biomass and shifts in community composition (reduced abundance of endemic boreal–temperate species, increased abundance of mid-California neritic and oceanic species). Toward the seaward end of the section (P08–P12), changes of zooplankton species composition were much less apparent, and the main signal associated with the 1997–1998 event was an early and narrow spring peak of Neocalanus spp. Although most extreme in 1998, both the nearshore and offshore sets of anomalies were continuations of trends that had developed progressively off British Columbia through the 1990s. A few taxa, normally endemic to southern parts of California Current and previously absent or very rare off British Columbia, appeared in our samples in 1997–1998 and persisted through summer of 1998 and at some locations into 1999. The changes observed over the continental slope of Vancouver Island were very similar to the observations of 1970s versus late 1990s differences in the zooplankton of the central Oregon coast continental shelf (PICES Sci. Rep., 10 (1999) 45; Prog. Oceangr. (2002)), suggesting that there was alongshore continuity of both oceanic forcing and zooplankton response.