MEPS 215:213-224 (2001)  -  doi:10.3354/meps215213

ABSTRACT: The stability of the species composition of calanoid copepods was investigated off southern California using samples collected during spring by the California Cooperative Oceanic Fisheries Investigations (CalCOFI) from 1951 through 1999. The region was consistently dominated in spring by 3 species, Calanus pacificus, Metridia pacifica and Pleuromamma borealis, which together accounted for 77% of the total on average. Four other categories each usually accounted for 3 to 7% of the total, but were occasionally much more abundant. All other species each generally made up less than 1% of the total. Species composition was compared between pairs of cruises using the percent similarity index (PSI). Species composition was found to be stable over the 49 yr covered by the study. Mean PSI values for each cruise were consistently high, except for 6 anomalous years, 1951, 1977, 1978, 1983, 1992 and 1998. The increased frequency of anomalous years following the 1976/1977 climatic regime shift, rather than an overall decline in similarity, may account for the difference in PSI means before and after the regime shift. Of the 6 anomalous cruises, 3 coincided with strong California El Niño events during the warm-water period of the 1980s and 1990s, while 2 occurred immediately after the 1976/1977 regime shift.

KEY WORDS: Species composition · Stability · Percent similarity index · Copepoda · Calanoida · California Current System