GULF OF MEXICO 



229 



prepared to give consistent attention to the 

 studies of diatoms and were primarily concerned 

 with other problems. Mention may be made here 

 of the observation by Willis Hewatt of Texas 

 Christian University (personal communication) 

 that Biddulphia mobilensis periodically produces 

 very heavy concentrations off the Louisiana coast 

 near Grand Isle. This area, and probably also 

 the coasts of Alabama to Texas, would seem to be 

 optimum environment for this species. 



DIATOM FLORAS OF GULF AND 

 ADJACENT WATERS 



At the present state of our Imowledge there is 

 no basis for correlating diatom floras of the Gulf 

 and adjacent areas or for discussing theii- mutual 

 effects. Currents that swing into the Gulf from 

 the Caribbean on the southeast and out through 

 the Florida Straits on the northeast must, of 

 course, carry their complement of plankton dia- 

 toms; but, until more is known of both the Gulf 

 diatom flora and that of the adjacent waters 

 outside, no definite information can be given 

 regarding the effect of one on the other. As has 

 been said, practically nothing is known specifically 

 of the Gulf diatom plankton or, for that matter, 

 of that in adjacent tropical waters. 



The mere presence of similar population con- 

 stituents in the adjacent areas does not necessarily 

 imply any direct relationship between them. It 

 is quite possible that the greater sweep of the Gulf 

 Stream tends to some extent to isolate the Gulf 

 of Mexico from the adjacent seas despite the 

 movement of some of the Atlantic and Caribbean 

 waters through the Gulf. 



With the bottom-living and attached species 

 seemingly not so readily subject to dispersion, 

 there is not enough difference of conditions, say, 

 on the east and west coasts of Florida or the 

 envu'ons of Cuba, and there is so much correspond- 

 ence in certain conspicuous species, such as 

 Terpsinoe musica, T. americana, Nitzschia para- 

 doxa, Grammatophora marina, Biddulphia penta- 

 crinus, Baphonevt surirella, Surirella reniformis, 

 and members of the genera Coscinodiscus, Cam- 

 pylodiscus, Biddulphia, Navicula, that in our present 

 state of limited knowledge it is not feasible to give 

 any general statements of significant relationship. 

 It would seem that a very large variety of species 

 find the waters both inside and outside the Gulf a 

 suitable habitat, but it will take a great deal of 



more detailed collecting and comprehensive study 

 to disclose any significant floristic differences or 

 migrational influences within these areas. 



ECOLOGY 



The literature on the diatoms of the Gulf area 

 contains practically nothing concerning their 

 ecology and economic importance. The designa- 

 tion of species as fresh water, brackish, or marine 

 is about the extent of ecological data. Yet, both 

 subjects should be of great interest. One may 

 expect that careful studies of many diverse habi- 

 tats represented along the shorelines of the Gulf, 

 and in its open waters could give valuable data 

 regarding habitat characteristics, optimal range 

 of the different species, and their seasonal occur- 

 rences. 



The effects of the discharge of particulate matter 

 by the Mississippi and other large rivers on the 

 distribution and productivity of diatoms in the 

 open waters constitutes another important 

 problem. 



Relation of the diatoms as a vital chain in the 

 marme food cycle is also of great interest because 

 of the extensive shi'imp. oyster, and fishery 

 industries of the area. 



Such ecological studies of the diatoms correlated 

 with theu- floristic survey may well contribute to 

 general knowledge of the Gulf and will be helpful 

 in understanding its specific problems. 



PRODUCTIVITY 



It has long been held that productivity of plank- 

 ton diatoms in tropical and subtropical waters is 

 in general lower than in colder regions. This, in 

 the writer's experience, appears to be generally 

 true, but the statement should be taken with 

 some qualifications for there are instances in 

 which, owing to a particular combination of local 

 conditions, it does not hold. Even in tropical 

 waters certain areas may contain heavy concen- 

 trations of diatoms. There is for instance evi- 

 dence of occasional unaccoinitable surges of cer- 

 tain species, as Hemidiscus. Biddulphia mobilensis 

 and Isthmia capenms about Tortugas and in othei' 

 places for which the causative factors are not 

 known. Because of the presence of very delicate, 

 transparent and minute forms that pass through 

 the meshes of the plankton net, the Gulf plankton 

 may at times contain a greater number of indi- 

 vidual diatoms and be more productive than 



