ARTIU'K DISTRIBUTION AND AHI'NDAM 'K OK Ml( 'RO( 'OI'KPODS 



was accomplished by first measuring the total 

 fluid volume of the sample, then stirring it vigor- 

 ously to disperse the material, then drawing off 

 a convenient amount for examination, and finally 

 measuring the remainder in order to determine 

 what percentage the subsample was of the orig- 

 inal sample. 



FAUNAL AREAS IN THE 

 CALCOFI SECTOR 



Although the primary purpose of the micro- 

 plankton program was a quantitative appraisal 

 of the microcopepod fauna, a few prominent cope- 

 pod species were routinely recorded. One of these, 

 Mecynocera clausii, proved useful as an indicator 

 organism allowing the CalCOFI sector to be 

 roughly divided into two plankton faunal areas, 

 onshore and offshore. 



Mecynocera is a monotypic genus. It can readily 

 be distinguished from other copepods by its excep- 

 tionally long first antennae (Mori 1964). Its small 

 size (about 1 mm) places it within the micro- 

 copepod range. These attributes make it conve- 

 nient and useful as an indicator of conditions 

 affecting the microcopepod fauna. Mecynocera 

 clausii has been reported near the surface 

 throughout tropical areas of the oceans, as well 

 as in temperate areas such as the Mediterranean. 

 In the CalCOFI area its presence may be consid- 

 ered as indicating the more tropical offshore and 

 southern waters. 



A typical distribution of M. clausii off southern 

 California and off northern and central Baja Cal- 

 ifornia is illustrated by data for February 1951 

 (Figure 1). Mecynocera is characteristic of off- 

 shore water whereas the occurrence of plutei of 

 benthic echinoderms may indicate coastal water. 

 The two boundaries tend to interdigitate, which 

 must imply alternating tongues of warm offshore 

 water penetrating toward the coast and jets of 

 cold onshore water moving out to sea. The 15°C 

 isotherm supports this interpretation. 



Submergence of the water of the California Cur- 

 rent under the offshore subtropical water may be 

 indicated at stations where Mecynocera and 

 plutei were taken together. This would result if 

 the net in its 130-m deep track caught Mecynocera 

 near the surface and plutei at some depth where 

 the submerging water had carried them. 



The shoreward boundary of Mecynocera, as 

 determined by the various cruises, is presented 

 in Figure 2. In general, the average boundary is 



•35° 



-30° 



120° 

 _i_ 



• ' 



FIGURE 1. — Distribution of Mecynocera clausii and pluteus 

 larvae during CalCOFI cruise for February 1951 off California 

 and Baja California. 



found about 400 km offshore in the San Francisco 

 area and inclines toward the coast farther south. 

 In the northern Baja California area it may im- 

 pinge upon the shoreline, but it becomes erratic 

 in the turbulent Punta Eugenia area. 



ZONE OF COPEPOD 

 NAUPLII MAXIMUM 



For a given cruise, if each line is examined and 

 the station which contained the greatest concen- 

 tration of nauplii is circled and the circled stations 

 for the various lines are connected, one obtains a 

 line of maximum copepod nauplii concentrations. 

 Figure 3 presents a typical distribution of copepod 

 nauplii and their maximum zone in the Channel 

 Island area. Two stations have been circled for the 

 line extending offshore from San Diego. It is com- 

 mon to find a high local concentration at stations 

 near the coast and a second high offshore particu- 

 larly in the area north of Point Conception. Had 

 the station pattern extended closer to the beach, 

 higher concentrations of nauplii probably would 

 have been encountered there. During a 5-mo 



603 



