MULLIN ET AL.: VERTICAL STRUCTURE OF PLANKTON OFF CALIFORNIA 



dominated by "large" rather than "small" prey. 

 That these types of zooplankters are less abundant 

 very near surface and below 30 m than at inter- 

 mediate depths is apparently not unusual in 

 spring ( Fiedler 1983:fig. 5). Both types of prey were 

 more abundant after the storm. Total food for both 

 types of larvae tended to be concentrated nearer 

 the surface in the poststorm condition. 



Although the numbers of larval fish in our sam- 

 ples are too small, especially after the storm, to 

 provide a strong test of spatial correlation with 

 their food supplies, the tau coefficients of correla- 

 tion between total larval fish and their food by day 

 were positive in all cases, but somewhat less so 

 after the storm for the nonthecate dinoflagellates 

 and ciliates which dominated the food supply of 

 "anchovy-like" larvae. This was the case even 

 though the poststorm distributions of both larval 

 fish and food were concentrated nearer the surface 

 than were the prestorm distributions. 



SUMMARY AND DISCUSSION 



We concentrated during this study on the con- 

 sequences of the vertical distributions of plankton 

 for the production of zooplanktonic food for larval 

 fish, and on the differences in distributions of food 

 experienced by larval fish at one coastal location 

 before and after a small storm. Since advection 

 surely occurred, we do not intend to imply that the 

 same individual larvae experienced both sets of 

 conditions. 



Conclusions we believe to be ecologically sig- 

 nificant and statistically verified are as follows: 



1. The biotic environment was vertically struc- 

 tured. 



a. Of the 28 zooplanktonic taxa for which the 

 ANOVA was appropriate, 22 had a consis- 

 tently uneven (i.e., stratified) pattern of dis- 

 tribution with depth in the upper 50 m. Of 

 the remaining six taxa, three had regular 

 temporal changes in vertical distribution. 

 Hence, only 3 of the 28 taxa were uniformly 

 distributed both vertically and dielly. 



b. Chlorophyll was stratified in the upper 50 

 m, and 9 of the 18 phytoplanktonic- 

 protozoan taxa examined had stratified dis- 

 tributions in the upper 40 m; the stratified 

 taxa were notably dinoflagellates and the 

 oligotrich ciliates rather than the dia- 

 toms. 



c. Both small prey and total prey for 

 "anchovy-type" larvae were vertically 



stratified, but prey for "mackerel-type" lar- 

 vae was not. 

 d. Though the abundance of Acartia was cor- 

 related vertically with that of chlorophyll, 

 its gut fullness was not. 



2. Several features were different after the storm. 



a. Several zooplanktonic taxa — notably, vari- 

 ous nauplii — were more abundant, while 

 larval fish were less so. Ceratium, Prorocen- 

 trum, and Lohmannlella had increased, 

 while several diatoms had decreased. Evi- 

 dence suggested a poststorm increase in 

 chlorophyll, but contained ambiguities. 



b. Several zooplanktonic taxa — Pleuro- 

 mamma at night, cyphonautes by day, 

 Calanus CII and CIII, larval fish — tended 

 to be concentrated in shallower depths after 

 the storm, as did chlorophyll, but data were 

 insufficient to show that the large-sized 

 phytoplanktonic taxa we studied responded 

 in this way. Food for both types of larval fish 

 was concentrated in shallower water after 

 the storm. The neustonic distribution of 

 Labidocera nauplii and copepodites was 

 less pronounced after the storm, but in gen- 

 eral the poststorm vertical stratification 

 was at least as great as that prestorm, even 

 though the temperature gradient was les- 

 sened. This general conclusion was also 

 true for phji^oplankton (except for some 

 diatoms which were less abundant after the 

 storm) and for the sum of forms represent- 

 ing "large food" for "anchovy-like" larvae 

 and "small food" for "mackerel-like" larvae. 



3. Relations between predators and prey were dif- 

 ferent following the storm. 



a. Several taxa maintained or established 

 abundant populations in those parts of the 

 water column where food was most plenti- 

 ful. However, this was not true for taxa with 

 pronounced diel vertical migrations. The 

 estimated poststorm reproduction of 

 "Paracalanus" was less limited by food than 

 was the prestorm reproduction, and 

 Calanus could obtain sufficient food for 

 growth in a greater fraction of the water 

 column after the storm; but we could not 

 demonstrate a poststorm increase in gut 

 fullness of large herbivores. 



b. Larval fish, both those categorized as 

 "anchovy-like" and "mackerel-like", also 

 were exposed to augmented concentrations 

 of their respective "large" food items, both 

 immediately and perhaps as a result of en- 



163 



