ARTHUR: DISTRIBUTION AND ABUNDANCE OF MICROCOPEPODS 



average of 13.27/liter. Size distribution as calcu- 

 lated from the data of Yokota et al. (1961) is: 



Width of nauplii 



All sizes 



>50 pm 



>100 pm 



>150 fim 



>200 fxm 



Average number/ liter 

 13.27 

 3.87 

 0.53 

 0.10 

 0.05 



In comparing the Kyushu to the California area 

 it appears that there are fewer very small nauplii 

 but about twice as many larger nauplii. These 

 differences may result from the Kyushu samples 

 being taken at the surface whereas the California 

 samples were collected at varying depths. 



Usual densities of total nauplii and copepodids 

 of all sizes calculated from the several investiga- 

 tions discussed herein are as follows: 



Nauplii/ Copepodids/ 



Source 

 This report, Equation (3) 

 Averaged from Yokota et al. 1961 

 Averaged from Beers and Stewart 1967 

 Averaged from Beers and Stewart 1970 



The calculated number of nauplii of all sizes 

 from this report appears to be somewhat high 

 which may result from being derived by extrap- 

 olating from Equation (3). The average number 

 of copepodids found by Beers and Stewart (1967) 

 appeared to be much higher than the other inves- 

 tigations and may be a result of sampling an un- 

 usually rich but short-lived condition (all samples 

 were taken during a 7-day period). Numbers of 

 nauplii and copepodids of Beers and Stewart 

 (1970) should be somewhat higher than the av- 

 erage for coastal areas because they were taken 

 very close to the beach. In general, the usual den- 

 sities in onshore areas at these latitudes (30°- 

 35°N) is about 1.5 to 4 copepodids/liter and about 

 13 to 30 nauplii/liter. These densities are similar 

 to those found by Allen ( 1939) who, while studying 

 phytoplankton off California by trapping 5-liter 

 samples, found that the combined densities of 

 nauplii and copepodids ranged from 10 to 30/liter. 

 Copepod nauplii average about 20-30/liter in 

 Japanese coastal waters and 10 or less/liter in 

 the warm offshore Kuroshio (Honjo et al. 3 ' 4 ). 



These densities are considerably lower than 

 those usually reported to be required to support 

 growth of marine teleost larvae in the laboratory 

 as is illustrated by a few examples. O'Connell 

 and Raymond (1970) found poor survival of an- 

 chovy larvae in densities of nauplii and copepodids 

 of less than 4,000/liter. Hunter (in press) used 

 100,000 Gymnodinuml liter combined with 8,000 

 to 115,000 rotifers/liter to grow early anchovy 

 larvae. Houde (1975) found best survival of larval 

 sea bream, Archosargus rhomboidalis, was on 

 50- to 100-pm wide nauplii and copepodids in 

 densities of 1,500-3,000/liter, but 10% survived 

 at 100/liter at low larval stock densities. In coastal 

 and offshore areas even the highest densities of 

 nauplii reported do not equal those used in most 

 laboratory rearing experiments. The highest con- 

 centration of larger than 56-/xm nauplii I encoun- 

 tered was 17.28/liter which indicates that, calcu- 

 lating from Equation (1), for nauplii of all sizes 

 there were about 195/liter. Highest concentra- 

 tions reported by others are 524/liter (Yokota 

 et al. 1961), 180/liter (Beers and Stewart 1970), 

 and 134/liter (Allen 1939). 



Gallagher and Burdick (1970) calculated that 

 the mean distance R, between a particle and its 

 nearest neighbor in a random three-dimensional 

 array can be computed from R = 0.553960p ', 

 where p is their mean density in space. At concen- 

 trations of 25 nauplii/liter the distance from the 

 mouth of a fish larva to the nearest nauplius is 

 on the average about 18.9 mm, whereas at 200 

 nauplii/liter this distance is 9.5 mm. 



Concentrations approaching laboratory re- 

 quirements are encountered in localized condi- 

 tions, i.e., Schnack (1974) caught nauplii with a 

 55-pm net in numbers up to 917/liter in a shallow 

 fjord off the western Baltic. Lasker (1975) found 

 the dinoflagellate, Gymnodinum splendens, in 

 the ocean in high enough densities (20,000- 

 40,000/liter) to support life of early laboratory- 

 spawned anchovies. These densities were depen- 

 dent on stable oceanic conditions which were 

 quickly dispersed by a storm. 



The reason for the disparity between the ob- 

 served naupliar densities in the ocean and the 



3 Honjo, K., T. Kidechi, and H. Suzuki. 1959. On the food 

 distribution and survival of post larval iwashi-I-Distribution 

 of food organisms, the food of the anchovy and ecologically 

 related species along the southwestern Pacific coast of Honshu, 



Sept.-Nov. 1958. Reports on the major coastal fish investiga- 

 tions, and the investigations for forecasting of oceanographic 

 conditions and fisheries (Preliminary Report), February 1959, 

 7 p. Engl, transl. by S. Hayashi. 



"Honjo, K., T. Kitachi, and M. Kudo. 1957. Food of the post- 

 larvae of iwashi. Reports of the major coastal fish investigations 

 for 1956 (Preliminary Report) November 1957, 5 p. Engl, transl. 

 by S. Hayashi. 



609 



