NO. 10 DAWSON : MARINE ALGAE, GULF OF CALIFORNIA 195 



of being able to work casually at the water's edge when choosing desirable 

 specimens, must scan and pick hurriedly from exposed rocks or sustain 

 frequent immersions. 



EcoLOGic Considerations 



Setchell, in a series of papers (1915, 1920, 1922) on the temperature 

 relations of marine algae, has shown the primary importance of tempera- 

 ture in ecologic and distributional considerations of these plants. He rec- 

 ognized that the ranges of temperature to which marine plants are sub- 

 jected are in general much narrower than are those of land plants. Also, 

 in contrast to terrestrial plants, whose various parts are subjected to quite 

 different temperatures at a given time, the marine plants are completely 

 surrounded by a medium of uniform temperature. The problems of tem- 

 perature for marine plants, thus, are relatively simple, and the ease with 

 which temperature can be measured makes some interesting correlations 

 possible. 



The seasonal variation in the temperature of surface waters along the 

 outer coasts of California and Mexico does not exceed 10° C. and is usu- 

 ally considerably below that figure. This coincides with Setchell's gen- 

 eral thesis as to temperature amplitudes in ocean waters (1915, 1920). 

 In the Gulf of California, however, we have not only latitudinal temper- 

 ature differences from south to north but exceptionally pronounced sea- 

 sonal differences far exceeding those known for any other waters of our 

 coasts (see p. 339). From winter to summer, amplitudes of tempera- 

 ture variation may reach as high as 25° to 28° C. Records made on the 

 Velero cruise, January 20-30, 1940, showed a gradual decrease in tem- 

 perature of surface water from San Jose del Cabo, 23° C, to San Felipe, 

 14° C. Scripps Institution data obtained over the same course from Feb- 

 ruary 13 to March 19, 1939, showed a range from 21.5° in the south to 

 between 15° and 17° in the north. A recording of the Zaca Expedition at 

 San Jose del Cabo, August 4, 1932, gave 26°-27° for surface water. The 

 writer's surface readings for July 18, 1940, were 31° on the reef at Tur- 

 ner's Island and 32°-33° along shore and in bays of adjacent Tiburon 

 Island. The highest temperature known to have been measured is a figure 

 of 36° C. obtained by the author in shore waters of Concepcion Bay, 

 Lower California, in mid- July, 1934. 



As soon as the extent of these seasonal temperature changes was re- 

 alized, it was strongly suspected that investigation would reveal a marked 

 seasonal alternation in the marine floras of northern parts of the Gulf. 



