GULF OF MEXICO 



165 



SURFACE CHLOROPHYLL CONTENTS 



H»«Vi» ONUS nn tlTER 



Figure 46. — Distribution of plant pigments in the waters of the northern portion of the Gulf of Mexico. 



was much less than that to be found in most 

 higher latitudes, the net plankton being ap- 

 proximately 1 percent of the spring bloom con- 

 ditions in the English Channel. The total 

 chlorophyll at the station that lay closest to 

 Loggerhead Key (it was the less productive of 

 Riley's two main stations) was only about 4 

 percent of the summer crop determined by the 

 same author in Long Island Sound by similar 

 methods. 



Riley (1938) also attempted to study produc- 

 tivity and limiting factors in productivity by 

 means of oxygen determinations in sea water 

 samples that had been confined in white and dark 

 bottles. To some of these, nitrates and phos- 

 phates had been added. He found that in the 

 waters of the Tortugas region the nitrates were 

 more important than the phosphates as limiting 

 factors in phytoplankton production. 



Parr (1939) made a quantitative study of 

 pelagic species of Sargassum in the western 

 North Atlantic, the Caribbean Sea, Cayman Sea, 

 and the Gulf of Mexico. Samples were obtained by 

 dragging a special net at the surface of the water 

 while the Atlantis was traveling from station to 

 station on hydrographic cruises. For each sample, 

 the catch was sorted as to species and weighed on 

 board ship. Within the Gulf of Mexico proper, a 

 total of 26 samples was obtained during the spring 

 months (February 16 to April 12) of 1935. To 

 obtain these samples, the net was dragged through 



the water for 1,230.5 miles. Sargassum was not 

 uniformly distributed in the Gulf. The outer 

 portions of the Gulf had a very sparse population 

 of the weed, whereas, the concentration in the 

 inner portion was second only to that of the 

 Sargasso Sea itself. Parr (op. cit.) calculated that 

 within the region of abundance, which he thought 

 to occupy about 90,000 square miles, the crop of 

 Sargassum amounted to approximately 1 ton per 

 square mile. 



The Sargassum crop, at the time of sampling 

 in the Gulf of Mexico, was in very poor physical 

 condition, the plants being small and moribund. 

 The occurrence of the maximum in the inner 

 portion of the Gulf, completely isolated as it 

 was from the primary maximum in the Sargasso 

 Sea by a wide expanse of Sargassum-poor water, 

 agrees with the results of hydrographic work 

 published by Parr (1935) and reported on else- 

 where in this book, to the effect that there ap- 

 pears to be no great volume of surface water 

 floating from the Gulf of Mexico to Florida 

 Strait during the period of examination. The 

 nearly complete isolation of the Gulf maximum 

 from the maximum of the Sargasso Sea is also em- 

 phasized by the fact that the epizoan fauna in the 

 two regions is very different. From his ob- 

 servations. Parr (1939) believes, however, that 

 the Gulf community is not a self-sustaining com- 

 munity in the same way that the Sargasso Sea 

 community is. He based this belief on the com- 



