4 MEMOIKS OF THE UNIVEKSITY OF CALIFORNIA 



The discoTery of tlie urmsiial amount of material of this group ■which has 

 been made br us in tlie waters off southern California is in part due to the 

 oceanographie conditions prevailing in oui* field of operations. These are seen 

 in the eupelagic area, that is, t^'pical ocean water of the high seas, little modified 

 by tributary streams and free from dominating coastal influences such as are 

 created by a much indented coast line or an extensive archipelago. 



The temiDeratures during the months of July and August at the surface 

 of the sea off La Jolla range from nineteen to twenty-one degTees Centigrade 

 (McEwen, 1916). These are characteristic of warm temperate seas. The 

 salinities are free from disturbances l\v discharge from rivers or by local rains 

 dining this season. The upwelling of waters from below against the coast, and 

 apparently also against the steep slopes of the outer limits of the continental 

 shelf, eni-iches the surface levels off the California coast with nitrogenous com- 

 pounds brought up from the depths of the sea. Evidences of this enrichment 

 are to be seen in the wealth of the pelagic fisheries, in the submarine forests of 

 giant kelps, and in the recurrent outbreaks of red water due to the rapid de- 

 velopment and consequent enormous nmnbers of dinoflagellates, usually of 

 Gonyaulax poli/Jiedra, which recur yearly off the shores of southern California, 

 especially from Jiily to Septemlier. 



An additional oceanographie factor favoring the occurrence of the warm 

 water fauna off southern California during the summer months is the influence 

 of the inshore, north-bound, return current which moves northward along 

 Lower California in an increasing volume and to a higher latitude as the season 

 advances to the culmination of its northward flow in December or thereabouts. 

 This tends to bring more tropical contributions to the offshore plankton, as 

 well as to bring alDOut a rise in temperature. 



This combination of stable, favorable oceanographie features constitutes an 

 ideal environment for these delicate organisms, attuned as they are to environ- 

 mental changes of small amplitude. Owing to the rapid increase in depth off- 

 shore and to the slight modifications of the shore line, the conditions of the 

 littoral zone adverse to pelagic life are confined to a relatively narrow belt 

 off the California coast, so that the pure water of the high seas with its fairly 

 stable conditions of temperature and salinity, and freedom from detritus and 

 continetital wastes, is to he found within a few miles of the laboratory of the 

 Seripps Institution for Biological Research at La Jolla. Few institutions and 

 few localities in the world are so favorably located for the study of this group 

 as is the laboratory at La Jolla. 



Material axd Collectioxs 



The material upon which these studies are based was obtained for the most 

 part in the summer of 1917, from June 1 to August 25. The organisms were 

 obtained in the first place in towings made with a plankton net of Xo. 12 silk 

 towed at the surface along the new pier at the Biological Station, about one 



