YOUNGBLUTH: VERTICAL DISTRIBUTION OF EUPHAUSIIDS 



ton, daylight penetrates further into the ocean 

 causing the migrating animals to descend deeper. 

 In the turbid water associated with high standing 

 crop, the migrating forms remain closer to the 

 surface." Observations on the vertical distribution 

 and daily movements of one euphausiid species in 

 this study lend support to this hypothesis. In more 

 turbid, upwelled water near the coast where 

 standing stocks of phytoplankton were greater 

 (e.g., CalCOFI 50.80), populations of juvenile E. 

 paciftca were larger and extended over wider 

 vertical ranges but their diel vertical migrations 

 were not pronounced. In clearer, more oligotrophic 

 waters farther offshore (e.g., CalCOFI 50.110; SOE 

 16, 47, 74), populations were reduced in size, 

 occupied deeper, usually narrower depth intervals, 

 and daily vertical movements were more obvious. 

 From these few observations it appears that 

 density levels and migration intensities of this 

 species may be coupled with the standing stock of 

 phytoplankton in surface waters. 



The persistence of nonmigrating forms, e.g., 

 Stylocheiron spp., within the same, relatively 

 narrow depths day and night in waters of varying 

 origin and the recurrence of the finding in this and 

 other studies (Brinton 1967; Youngbluth 1975) that 

 only a portion of a population categorized as a 

 migrating form, e.g., Euphausia spp., may ac- 

 tually make daily vertical movements to surface 

 waters, suggest that factors in addition to tem- 

 perature and light act to regulate the distributions 

 recorded. These observations indicate that more 

 attention should be directed toward sampling 

 those horizons where zooplankton populations are 

 concentrated to determine how distributional and 

 behavioral patterns are structured by the physical 

 and biological fluctuations within their preferred 

 habitats. 



ACKNOWLEDGMENTS 



I thank Malvern Gilmartin, John H. Martin, and 

 Donald P. Abbott for their suggestions and crit- 

 icisms. Pete Davoll, Dan Essin, Mel Malkoff, Tom 

 Malone, and Robie Robison helped set and recover 

 the Bongo nets aboard the RV Proteus. Support 

 for ship time, gear, and data analyses was provid- 

 ed in part by NSF grants GB 8374, GB 8404, GD 

 27254, and GA 28306 and in part by an NSF 

 predoctoral dissertation grant GA 29056. CalCOFI 

 samples were obtained through the program at the 

 Scripps Institution of Oceanography. 



LITERATURE CITED 



Alton, M. S., and C. J. Blackburn. 



1972. Diel changes in the vertical distribution of the eu- 



phausiids, Thyxanoessa spinifera Holmes and Euphausia 



pacifica Hansen in coastal waters of Washington. Calif. 



Fish Game 58:179-190. 

 Alvarino, a. 



1965. Distributional atlas of Chaetognatha in the California 



Current region. Calif. Coop. Oceanic Fish. Invest., Atlas 3, 



291 p. 

 Baker, A. de C. 



1970. The vertical distribution of euphausiids near Fuer- 

 teventura, Canary Islands ('Discovery' SOND Cruise, 

 1965). J. Mar. Biol. Assoc. U.K. 50:301-342. 



Banse, K. 



1964. On the vertical distribution of zooplankton in the 

 sea. Prog. Oceanogr. 2:53-125. 

 Barham, E. G. 



1957. The ecology of sonic scattering layers in the Monterey 

 Bay area. Stanford Univ., Hopkins Mar. Stn. Tech. Rep. 1, 

 182 p. 

 Berner, L. D., Jr. 



1957. Studies on the Thaliacea of the temperate northeast 

 Pacific Ocean. Ph.D Thesis, Scripps Inst. Oceanogr., Univ. 

 Calif., San Diego, 144 p. 

 1967. Distributional atlas of Thaliacea in the California 

 Current region. Calif. Coop. Oceanic Fish. Invest., Atlas 8, 

 322 p. 



BlERI.R. 



1959. The distribution of the planktonic Chaetognatha in 

 the Pacific and their relationship to the water masses. 

 Limnol. Oceanogr. 4:1-28. 



Boden, B. p., M. W. Johnson, and E. Brinton. 



1955. The Euphausiacea (Crustacea) of the North Pacific. 

 Bull. Scripps Inst. Oceanogr., Univ. Calif. 6:287-400. 



Boden, B. P. and E. M. Kampa. 



1967. The influence of natural light on the vertical migra- 

 tions of an animal community in the sea. Symp. Zool. Soc. 

 Lond. 19:15-26. 



BoLiN, R. L. and D. p. Abbott. 



1963. Studies on the marine climate and phytoplankton of 

 the central coastal area of California, 1954-1960. Calif. 

 Coop. Oceanic Fish. Invest., Rep. 9:23-45. 



Brinton, E. 



1960. Changes in the distribution of euphausiid crustaceans 

 in the region of the California Current. Calif. Coop. 

 Oceanic Fish. Invest., Rep. 7:137-146. 



1962a. The distribution of Pacific euphausiids. Bull. Scripps 



Inst. Oceanogr., Univ. Calif. 8:51-269. 

 1962b. Variable factors affecting the apparent range and 

 estimated concentration of euphausiids in the North 

 Pacific. Pac. Sci. 16:374-408. 

 1967. Vertical migration and avoidance capability of eu- 

 phausiids in the California Current. Limnol. Oceanogr. 

 12:451-483. 

 Gushing, D. H. 



1971. Upwelling and the production of fish. Adv. Mar. Biol. 



9:255-334. 

 Day, D. S. 



1971. Macrozooplankton and small nekton in the coastal 

 waters off Vancouver Island (Canada) and Washington, 



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