PHYTOPLANKTON OF THE GULF OF MEXICO 



By Charles C. Davis, Western Reserve University 



As late as 1944 Dr. B. F. Osorio Tafall, writing 

 concerning the interesting (iistribution of Bid- 

 dulphia siJiensis Greville, found it necessary to 

 speak of "La carenzia absoluta do estudios sis- 

 temjiticos del plancton en aiios anteriores en las 

 aguas del Caribe y del Golfo de Mexico ..." 

 It is true still that little has been done on tax- 

 onomic studies of Gulf of Mexico phytoplankters, 

 and even fewer ecological studies have been made. 



The earliest published observations on the 

 phytoplanktbn of the Gulf of Mexico appear to 

 be those of Alexander Agassiz (1888) who men- 

 tioned, in very general terms, the occurrence of 

 Coccolithophoridae in the central regions of the 

 Gulf. He mentioned more specifically the occur- 

 rence of large chains and patches "of dh-ty yellow 

 color" of the filamentous blue-green alga he 

 identified as "probably" the same as the Tri- 

 chodesmium erythraeum that is so famous in the 

 Red Sea. Dr. Drouet of the Chicago Natural 

 History Museum has identified the most common 

 filamentous blue-green alga from Florida and Texas 

 marine waters as Skujaella [Trichodesmium] 

 thiebauti (Davis, 1950), and probably this is the 

 species referred to above. Agassiz also referred to 

 the occurrence everywhere, but in small patches 

 only, of a species of Sargassum. 



From the time of Agassiz' (op. cit.) early super- 

 ficial report until 1937 there were no detailed 

 reports on Gulf of Mexico phytoplankters other 

 than individual species records such as that of 

 Taylor (1928) who listed the occurrence of 

 Skujaella [Trichodesmium] thiebauti and of two 

 common pelagic species of Sargassum (S. natans 

 and S. fludtans) near or at the Tortugas Labora- 

 tory. In addition, there were certain other 

 studies made at the Tortugas Laboratory which, 

 however, appear not to have been reported in 

 detail. Thus, Grave and Burkenroad (1928-29) 

 reported diatoms among those plankters that were 

 abundant or that occurred regularly, while Conger 

 (1925-26, 1926-27, 1927-28, 1928-29, 1937-38, 

 1938-39) briefly summarized his work on diatoms, 



259534 0—54 



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some of them plaiiktonic. Conger (1926-27) 

 found that the diatom flora of the Dry Tortugas 

 was sti'ongly local in character and that it had 

 its nearest affinities to the West Indian flora. 

 His (Conger 1937-38) investigations showed that 

 there was Tittle change of quantity or kinds of 

 the planktonic diatoms during his 10-week (sum- 

 mer) stay at the laboratory except that there was 

 "some slight increase" in abundance after a period 

 of heavy wind. He emphasized that the region 

 of the Dry Tortugas is a silica-poor region and 

 that Si is a limiting factor there in diatom pro- 

 duction. For comparative purposes he (Conger 

 1927-28) also studied some samples from Tampa 

 Bay and found the water rich with plankton. 

 He stated that the "richness of this area in diatoms 

 may account for the abundance of marinelife there." 

 Riley (1937, 1938) studied phy to plankton pro- 

 duction in Gulf waters, largely through the plant 

 pigment method. In his former report (Riley 

 1937) he considered the influence of the Mis- 

 sissippi River drainage upon the phytoplankton 

 in the northern portion of the Gulf. A number 

 of stations were established from Galveston to 

 Mobile and south to the thousand-fathom line 

 (fig. 44). Analyses were made of salinity, phos- 

 phate, copper, plant pigments, and weight of 

 organic matter. It was found that the water 

 of the Mississippi River itself was very rich in 

 phosphates and that this water spread over the 

 surface of the northern Gulf both to the east and 

 to the west but especially to the east in the direc- 

 tion of Mobile (fig. 45). Plant pigments were 

 highest in the waters richest in phosphates (fig. 

 46). Samples obtained from completely fresh 

 river water contained higher values for plant 

 pigments than elsewhere, but these values were 

 not especially high for fresh waters. This in- 

 dicated that the high turbidity of the river water 

 was a deterrent to phytoplankton growth, for 

 nutrient conditions were especially favorable for 

 phytoplankton production. Analyses in the open 

 Gulf showed typically low values. 



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