410 JOHNSON AND BRINTON [CHAP. 18 



within limits. Some information is, therefore, provided that can be of aid in 

 considering the source, direction, time lapse or complexity of currents. During 

 the growth of larvae there is often a succession of well defined stages (or sizes) 

 which, when well known, are further aids in considering the source and time 

 of larval entrance into the waters as floating organisms. The information on 

 water currents that can be gleaned from a study of the distribution of these 

 larvae cannot, as a rule, be expected to indicate a direct line of flow, and thus 

 to provide a clear-cut answer as to the source and time involved. More often, 

 the occurrence of the larvae gives only partial answers and poses problems that 

 need clarification through more detailed oceanographic investigations. They 

 often bring to light oversimplifications that are likely to be introduced in 

 dynamic computations of flow. Thus, more questions about water currents 

 may often be asked than are answered; but this is an important contribution, 

 for it is widely recognized that in oceanographic research questions must first 

 be asked of the sea before answers are obtained. 



The implications of a study of this kind are well illustrated by a seven-year 

 investigation of the occurrence of the floating larvae of the California spiny 

 lobster (Panulirus ivJerruptus). In this survey it was found that it requires 

 about 7f months to complete the planktonic larval life in which there are a 

 succession of 11 larval stages (Johnson. 1960). During this relatively long, 

 hazardous time, the larvae are at the mercy of prevailing currents. A charac- 

 teristic picture of the geographic distribution of various larval stages is given 

 in summary form in Fig. 13. 



In the light of this long larval period, it is remarkable that the lobster fishery 

 on the California coast remains as stable as it does. Precisely what are the details 

 of circulation that enable retention of sufficient numbers of larvae to bring 

 about restocking in the area? A priori, it appears that the system of eddies and 

 countercurrents that retard outflow from the area is far more complicated than 

 usually pictured on the basis of computations giving dynamic topography. 

 Although major eddies are usually clearly detected by this method, the direc- 

 tion and rate of surface flow suggest that it would be unlikely that any con- 

 siderable packet of water and its contained larvae would remain for seven to 

 eight months within the distributional area of the adult lobster on the Southern 

 California and Baja California coasts. Only a few drift bottles set adrift 40 

 miles from the coast to test the currents have been recovered, and the inshore 

 current is said to flow southward from March through October (Reid, Roden 

 and Wyllie, 1958). Nevertheless, the biological data, although evidencing a 

 dispersal from the shore where the larvae are hatched, do show that there must 

 be a fair retention of larvae, and in addition to this retention within the 

 area, a mixture of larval stages does at times occur in a single sample. 

 This would indicate a great deal of mixing within the water by eddy dif- 

 fusion . 



In the interpretation of the meaning of the distribution of these larvae (and, 

 indeed, also of the holoplankton) in terms of water movements, it is important 

 to have in mind at all times that here one is dealing with living creatures that, 



