MULLIN ET AL.: VERTICAL STRUCTURE OF PLANKTON OFF CALIFORNIA 



ably greater fraction of total reproduction oc- 

 curred at maximal (i.e., nonfood-limited) rates 

 after the storm. 



A similar quantitative example of augmenta- 

 tion of zooplanktonic nutrition related to the 

 storm can be calculated for CIV-adult Calanus, 

 though the vertical distribution of these stages 

 was not well correlated with that of chlorophyll. In 

 June 1980, Cox et al. (1983) estimated the carbon 

 budget of Calanus at various stations and depths 

 in the Southern California Bight, and concluded 

 that gain in biomass of these copepods was possi- 

 ble where the concentration of chlorophyll ex- 

 ceeded 0.9 Mg/1- By this standard, the fraction of 

 the upper 50 m where some gi-owth was possible 

 (nighttime only, because of diel migration) was 

 36% before and 58% after the storm. 



A third test of the significance of vertical dis- 

 tributions and the effect of the storm on them was 

 based on the plant pigments in the guts of the 

 large copepods caught at various times and 

 depths. The measurement of fluorescence of gut 

 contents can be used as a quantitative estimate of 

 the rate of ingestion of plant material if the break- 

 down of pigment, the gut passage time, and the 

 background fluorescence due to an animal's own 

 pigmentation are known (Mackas and Bohrer 

 1976). We chose to ask two simpler questions based 

 on changes in fluorescence: 1) Were the total gut 

 pigments (chlorophyll -I- phaeopigments) of 

 copepods caught at specific depths correlated with 

 the concentration of chlorophyll measured at the 

 same depths, before or after the storm or both? 2) 

 Did the amount of gut fluorescence of a tax on, 

 independent of specific depths, change coincident 

 with the storm? The first question addresses the 

 issue of whether the copepods can be shown to have 

 fuller guts at depths where phytoplanktonic food 

 (as measured by chlorophyll) is more concen- 

 trated. If copepods move frequently from the 

 depths at which they feed, such correlations would 

 be difficult to establish (cf. Dagg and Wjmian 

 1983). The second question is the more general one 

 of whether the copepods were better nourished 

 after the storm. 



We tested data concerning female Acartia, 

 female and CV Calanus, female Metridia, and 

 female Pleuromamma in this regard, with 6-28 

 pre- or poststorm data points per taxon. Of these 

 taxa, only Acartia's abundance was significantly 

 positively associated with the vertical distribution 

 of chlorophyll (see above). 



The gut pigment per Acartia showed no relation 

 to the ambient concentration of chlorophyll, how- 



ever, while that of Pleuromamma was positively 

 correlated with chlorophyll. In no case was the 

 poststorm correlation (tau coefficient) between gut 

 fluorescence and chlorophyll stronger than that 

 prestorm. Hence, we could not show that for these 

 taxa the distribution of degree of satiety became 

 more strongly associated with the vertical dis- 

 tribution of chlorophyll after the storm, even 

 though the range of chlorophyll concentrations 

 available in the upper 50 m had increased. 



Nor for any of these taxa was the poststorm 

 amount of gut fluorescence significantly greater 

 than that prestorm. Based on comparison between 

 field-caught female Acartia and Calanus, and 

 these same taxa fed to excess or starved in the 

 laboratory, we conclude that both these popula- 

 tions were well fed in general both before and after 

 the storm, and animals had plant food in their guts 

 at all depths sampled. Hence, we could not demon- 

 strate a change in nutritional status of the taxa as 

 a result of the storm, even though the overall con- 

 centration of chlorophyll increased. All these taxa 

 have been shown to feed on nauplii as well as 

 phytoplankton (e.g., Haq 1967; Lonsdale et al. 

 1979; Landry 1981), but we could not test whether 

 their nutrition from animal sources had improved 

 coincident with the increase in abundance of 

 nauplii following the storm. 



D. Abundance and Vertical Distribution of 

 Food for Larval Fish 



Because larval fish are visual predators, it is the 

 diurnal distributions of potential prey which are 

 particularly relevant. Different species select (or 

 are physically able to ingest) different prey, and of 

 course different types of prey differ in their catch- 

 ability, digestibility, and nutritive value. We will 

 consider the distributions of food for two prototyp- 

 ical larvae representing extremes in a continuum 

 of actual types. One is a small-mouthed larva 

 which we v^dll call "anchovy-like", based on Bemer 

 (1959), Lasker et al. (1970), O'Connell and 

 Raymond (1970), Arthur (1976), and Lasker and 

 Zweifel (1978). For these larvae, "large" prey con- 

 sists of all copepod nauplii and lamellibranch and 

 cyphonautes larvae (Appendix); "small" prey con- 

 sists of all ciliates and all nonthecate, large di- 

 noflagellates. Laboratory studies suggest the crit- 

 ical concentrations for both good survival and 

 rapid grov^rth are ^ 5 x 10^ large or s: 5 x 10^ small 

 prey 1~^ , or an equivalent combination. 



The other prototypical larva has a larger mouth 

 and is more active; based on Arthur (1976), Hunter 



161 



