FISHERY BULLETIN: VOL. 75, NO. 4 



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MONTHS 



FIGURE 3. — Annual cycle of totaled zooplankton abundance 9 

 and 18 km from the Oregon coast at Newport (NH 5 and NH 10) 

 during the 3-yr study period. 



and a winter low. In addition to that basic cycle, 

 there are peaks in total abundance at NH 1 in each 

 year of the study in either February or March. The 

 25 February 1970 sample had high numbers of 

 copepod nauplii other than Calanus (1,840 m" 3 = 

 27% of the total zooplankton). This indicates the 

 presence of an actively reproducing adult copepod 

 population. A diatom bloom was in progress at 

 that time as well. Our nets were clogged with the 

 diatom Thalassiosira. The 16 February 1971 peak 

 had high numbers of Pseudocalanus sp. (680 m~ 3 

 = 41% of the catch), Calanus marshallae (240 m -3 

 = 15%), and Calanus nauplii (192 m 3 = 12%). 

 The Pseudocalanus sp. population was almost 

 entirely stage I copepodites. These facts again in- 

 dicate actively reproducing adult copepod popula- 

 tions in late winter. In both of these years, abun- 

 dances decreased after the February peak to lower 

 values in March or April. In 1972 no samples were 

 collected in January or February. The 15 March 

 sample at NH 1 had high numbers of Pseudo- 

 calanus sp. (1,844 m~ 3 = 62%), Oithona similis 

 ( 690 m ~ 3 = 23% ), and Acartia longiremis (265 m " 3 

 = 9%). Half of the total catch were immature 

 Pseudocalanus sp. and half of the A. longiremis 



were immature. Again, there is some evidence of a 

 late winter cycle of reproduction of the species of 

 copepods permanently resident in the nearshore 

 zone and dominant later in the year. There is evi- 

 dence of this late winter peak in copepod abun- 

 dance at NH 3 only in 1970, and it is not seen at all 

 in the data for NH 5 and NH 10. 



The months of April and May are periods of 

 transition in the direction of the prevailing wind. 

 An atmospheric high pressure cell begins to form 

 over the North Pacific Ocean, and the winds begin 

 to blow from the north with greater frequency. In 

 all years of this study, heavy phytoplankton 

 blooms were observed at NH 1 during this period. 

 The blooms are probably associated with the re- 

 plenishment of nutrients within the photic zone by 

 the earliest brief episodes of upwelling. Dates with 

 dense blooms were 27 April 1970, 3 and 14 May 

 1971, 20 April 1972, and 22 May 1972. Zoo- 

 plankton abundances were low at these times. 



Seasonal Cycle of 

 Relative Species Abundance 



The seasonal cycle of relative abundance of the 

 most abundant species of copepods is shown in 

 Figure 4 for all four stations. The graphs for each 

 station represent cumulative percentage of the 

 total catch for the species as labelled. The result is 

 complex but deserves careful study because some 

 interesting patterns are present. The simplest 

 pattern is the sinusoidal annual cycle. This pat- 

 tern is in phase with the seasonal cycle of total 

 abundance. It can be concluded from comparison of 

 the zooplankton abundance plots (Figures 1, 2, 3) 

 and from the relative species abundance plot (Fig- 

 ure 4), that low numbers during winter months 

 are coincident with 1 ) a decrease in relative abun- 

 dance of the endemic copepod species and 2) an 

 increase in importance of warmwater species and 

 noncopepod taxa. In addition to copepods with 

 southern affinities, Oikopleura spp. and chaeto- 

 gnaths become important during the winter. 



There is marked seasonality in the relative 

 abundance of each taxon. This will be discussed 

 station-by-station. At NH 1 Pseudocalanus sp. 

 were numerically important during the upwelling 

 season, usually through August. Acartia clausii 

 and A. longiremis were always important during 

 the autumn after the cessation of upwelling. Cen- 

 tropages abdominalis was never a major compo- 

 nent after August, with the exception of 1971. 

 Calanus marshallae copepodites and nauplii were 



720 



