FISHERY BULLETIN: VOL. 83, NO. 2 



val fish food. Larger zooplankters represent poten- 

 tial competitors with larval fish for dinoflagellate 

 and protozoan prey, or even potential predators of 

 the larvae themselves. 



The vertical distribution of larval anchovy 

 within the euphotic zone is less well known than is 

 that of zooplankton, particularly with respect to 

 the vertical distribution of their food sampled con- 

 currently, because larval fish are so rare that nets 

 with large capacity must be used to capture sig- 

 nificant numbers of them. It was partly to provide 

 such data that we conducted the present study 

 concurrently with sampling by National Marine 

 Fisheries Service personnel from a second vessel 

 to determine the vertical distribution of larval 

 fish. Records of water temperature, concentration 

 of chlorophyll, and abundances of phytoplankton 

 at the depth of the chlorophyll maximum were also 

 taken from the second vessel, and are compared 

 with our results below. 



We were fortunate, intellectually if not physi- 

 cally, to sample a fixed location before and after 

 passage of a local storm (cf. Lasker 1975), and we 

 therefore tried to examine the potential impor- 

 tance for the food web of turbulent rearrangement 

 of vertical distributions. We looked for changes 

 coincident with the storm in overall abundances 

 and in the intensity and patterns of vertical 

 stratification of many planktonic taxa, and in cor- 

 relations between the vertical distributions of 

 predators and their potential prey. We then made 

 predictions concerning the implications of these 

 changes for the nutrition of larval fish. 



METHODS 



From mid-March to mid-April 1980, spawning 

 of anchovy was concentrated in the inner portions 

 of the Southern California Bight, apparently con- 

 fined by plumes of cool water extending south of 

 Point Conception beyond Santa Catalina and San 

 Clemente Islands (Lasker et al. 1981). Between 29 

 March and 6 April, we took 13 vertical series of 

 samples at 5 m intervals in the upper 50 m of water 

 at lat. 33°28.5'N, long. 117°46.7'W (CalCOFI sta- 

 tion 90.28, 3.5 km offshore from Dana Point, 

 California), where the depth of water was —350 m, 

 using the pump and hose described by Mullin and 

 Brooks (1976) and Mullin (1979). Almost all of the 

 larval anchovy at this station occurred in the 

 upper 40 m (Pommeranz^). Because of the re- 



stricted area of the anchovy's spawning at the 

 time, our results may be indicative of conditions 

 experienced by a considerable fraction of the lar- 

 vae produced in late March-early April in the 

 Bight. The volume of water filtered per quantita- 

 tive sample of zooplankton was typically 200-300 1; 

 for comparison, the rate at which a 1.5 cm larval 

 anchovy searches water for food is about 5 1/h 

 (Hunter 1972). In addition to quantitative, net- 

 concentrated samples of zooplankton and 

 fiberglass-filter concentrated samples of 

 chlorophyll, we preserved unconcentrated sam- 

 ples of water in 59c v:v Formalin"* for counts of 

 phytoplankton, and filtered nonquantitative sam- 

 ples of net-caught zooplankters onto fiberglass fil- 

 ters which were then frozen for later analysis of 

 plant pigments in the guts. 



One profile was completed during 0900-1400 h 

 and another during 2030-0030 h each 24-h day 

 except from 0000 on 1 April to 0900 on 3 April, 

 when a local storm kept us in port. Profiles 1-6 

 were "prestorm", 7-13 "poststorm". 



Analytical procedures for chlorophyll and net- 

 caught zooplankton followed Mullin and Brooks 

 (1976) and Mullin (1979). All recognizable zoo- 

 plankters were enumerated. For phytoplankton 

 and protozoans, we prepared a physically inte- 

 grated sample for each profile by mixing 50 ml of 

 water taken from each of the 11 depths. Fifty ml of 

 this integrated sample were settled for 48 h, and 

 cells were counted using the Utermohl method. 

 For cells —20 /u,m or greater (equivalent spherical 

 diameter), half the settled material was counted at 

 160 X magnification (equivalent to a 25 ml sam- 

 ple); for cells <20 /xm, one row across the diameter 

 of the settling chamber was studied at 625 x mag- 

 nification (0.33 ml). 



Subsequently, 50 ml aliquots from each depth 

 for each profile were settled at least 24 h and 

 examined. Since the flora was very diverse, we 

 selected a short list of taxa using the following 

 criteria: Cells were clearly identifiable even 

 after preservation in Formalin, present in suffi- 

 cient numbers to provide reliable data, and (with 

 several exceptions) of interest as possible larval 

 fish food. We believe that all taxa usable as food 

 were satisfactorily preserved and counted. Most of 

 the cells were counted using 160 x magnification, 

 usually in an equivalent of a 12.5, 25, or 50 ml 

 sample. Chaetoceros spp., Nitzschia spp., and 

 Emiliania {Coccolithus ) huxleyi were enumerated 



'Tilman Pommeranz, Institut fiir Meereskunde, Kiel, West 

 Germany, pers. commun. 1984. 



■"Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service. NOAA. 



152 



