OWEN ET AL.: SPAWNING AND SURVIVAL OF LARVAL ANCHOVY 



cm/s and 18.8 cm/s to 48.2 cm/s. Drift direction at 

 Site 2, predominantly longshore, indicated that 

 Site 2 larvae had been spawned offshore rather 

 than drifting out from an onshore spawning area. 

 The degree to which drifter displacements 

 paralleled one another at each site (Fig. 2) in- 

 dicated homogeneous, nondivergent flow of the 

 surface layer and general integrity of each water 

 corpus being investigated. Similar rates of sep- 

 aration of drifter pairs indicated no differences 

 between rates of lateral diffusion between sites. 



Vertical Structure 



Physical structure of the upper lOU m at both 

 sites exhibited no overall trends for the duration 

 of the study (Fig. 3). Variations of isopleth 

 depths in the pycnocline at Site 1 were greater 

 during the second half of the period, perhaps 

 owing to increased internal wave activity. 



A slight warming trend over the course of the 

 studies was indicated by increased surface layer 

 temperatures at both sites. The trend was likely 

 due to local heating of the mi.xed layer. Heat 

 content of the upper layer increased at Site 2 but 

 no trend was detected at Site 1. 



Local diurnal heating was apparent at Site 1 

 from continuous temperature records at 3 m 

 depth as well as from CTD casts. Higher winds 

 and a thicker mixed layer at Site 2 obscured 

 diurnal temperature variations. 



Vertical sections of phytopigments (Fig. 3) 

 gives a less conservative picture of variations. 

 Intensification of the maximum chlorophyll and 

 phaeopigment layers over the course of studies 

 occurred at both sites. In view of the lack of 

 change of temperature, salinity, and density 

 structure, the increase in pigment concentration 

 was likely due to local processes rather than to 

 advective processes. The change thus expressed 

 the net product of primary production and 

 grazing. 



Composite T-S diagrams (Fig. 4), constructed 

 from CTD cast data at each site, indicate that 

 the drifters were set into waters of different 

 structure and composition at the two sites. Site 2 

 water, closer in character to California Current 



core water (Lynn and Simpson in press), was 

 cooler and less saline than Site 1 water. Site 1 

 water was likely derived from a mix of California 

 Current core water (from the north, offshore) 

 and coastal countercurrent water (from the 

 south, nearshore), further modified by local 

 warming of the surface layers in transit. 



Plankton Quantity and Composition 



Within sites, no major differences were appar- 

 ent in plankton quantity or community composi- 

 tion along drifter paths. Over twice as many 

 plankton organisms were caught by 333 ixm 

 mesh nets at Site 1 than at Site 2, and predatory 

 copepods were 5 times more numerous at Site 1 

 than at Site 2 (Table 1). Plankton diversity was 

 somewhat higher at Site 1 than at Site 2: on 

 average. Site 1 tows yielded 144 invertebrate 

 species, whereas Site 2 tows yielded 130 species. 

 Perhaps the most striking difference in the zoo- 

 plankton was the high abundance of salps at Site 

 2. No direct interactions are known between fish 

 larvae and salps. 



In terms both of rations and numbers, over 

 twice as much larval anchovy food was caught by 

 75 iJim mesh nets at Site 1 than at Site 2 (Table 

 1). 



Summary 



To compare habitats at the two sites, Table 1 



^Lynn, R. J., and J. Simpson. 1989. The influence of bathy- 

 metry upon the flow of the undercuj-rent off Southern Cali- 

 fornia. Unpubl. manuscr. 



Figure 3. — Vertical time sections of temperature (t), 

 salinity (%c), density (cr,), and stabihty (E) at Sites 1 and 

 2. Vertical time sections of chlorophyll-a and phaeopig- 

 ment at Sites 1 and 2. 



33.4 33.5 33.6 33.7 33.8 

 SALINITY (%o) 

 Figure 4. — Composite T-S diagrams at Sites 1 and 2. 



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