GULF OF MEXICO 



179 



1928, an account of the al^ac of Florida, now 

 urgently in need of revision but giving keys, 

 descriptions, and many illustrations. Some of 

 the needed changes were incorporated in his notes 

 on Caribbean Marine Algae . . . (1942), where 

 keys and additional illustrations are given. For 

 My.xophyceae, Tilden's volume (1910) is still the 

 only general American source, but this will need 

 to be supplemented and corrected by that of 

 Geitlcr (1932) and the current publications of 

 Drouet. Outside of these few works, the in- 

 vestigator must rely on the great Sylloge Algarum 

 of De Toni (1889-1924) and on a few score of 

 brief papers scattered through botanical journals. 

 The chief reference collections containing algae 

 of the species found in the Gulf are easily desig- 

 nated. Most generally available are those dis- 

 tributed in Colhns, Holden, and Setchell's Phyco- 

 theca Boreali-Americana (1895-1919), of which 

 numerous sets are held in institutions about the 

 country, but in the use of these exsiccatae the 

 usual attention must be given to corrections in 

 nomenclature and identification. Many Florida 

 algae appear in this series. The main Curtiss 

 collection is in the U. S. National Herbarium. 

 Because of his early dominance of phycological 

 studies in America, Farlow accumulated valuable 

 early reference materials at Harvard University. 

 Howe did far more field work himself and acquired 

 CoUins' personal herbarium for the New York 

 Botanical Garden so that the Gulf collections 

 there are the most extensive in the country. The 

 writer in his personal collections and the herbar- 

 ium of the University of Michigan has a most 

 valuable resource. Wliile no other collections 

 in this country contain many specimens from this 

 area, one may list the very important herbaria 

 at the University of California and the Chicago 

 Natural History Museum, both of which have use- 

 ful auxiliary collections. 



CHIEF TYPES OF ALGAL VEGETATION 



Since for great stretches of the Gulf coast no 

 lists have been published, it is impossible to 

 tabulate known floras. By describing here the 

 more striking floristic elements of a few selected 

 types of locality, it is hoped that future students 

 may, through these characterizations, be guided 

 in what to expect under similar conditions. 



SHIFTING SANDY BEACHES AND ESTUARINE 

 MUD FLATS 



The great extent of the Gulf coast line which 

 consists of unconsolidated sand and mud militates 

 against the production of a complicated flora. 

 Where every wave turns over the sand or stirs up 

 a cloud of mud, algae do not colonize. Few 

 microscopic forms are able to live mixed with the 

 unstable sediments; few large species long survive 

 adrift above them, and these accidental elements 

 constitute no real flora. Such a region, regardless 

 of the chemical nature of the sediments, is con- 

 sistently an algal desert. The great areas of 

 recently transported silt in estuarine regions and 

 deltas are equally barren. 



STABLE SAND AND MUD; POOLS, SMALL 

 LAGOONS, AND COVES 



Wlien such sediments become stabilized, a 

 different situation is presented. If the tidal rise 

 and fall is considerable, broad zones of beach 

 which were immersed at high water of spring tides 

 are exposed at times of neap tide and such zones 

 may show an algal flora. If they receive enough 

 moisture from salt-marsh pools by percolation, 

 or from rain or by other means, they may support 

 a considerable and recognizable vegetation of such 

 Myxophyceae as Lyngbya aestuarii and Micro- 

 coleus chfhonoplastes, or on the surface mats of 

 Rhizoclonium riparium. Such a vegetation may 

 even be able to survive a little gentle wave action 

 undisturbed. Wliere silt transported by stream 

 movement in flood is left stable by recession, it, 

 likewise, may develop similar colonies in brackish 

 estuaries. 



When waves throw up barrier beaches of 

 calcareous sand and coral rubble, pools, or lagoons 

 are cut off in which surf action is absent and 

 tidal action greatly reduced or eliminated. Rains 

 serve to dilute the water, especially at the surface. 

 On sunny days, the temperature rises greatly. 

 Under such circumstances, few algae except 

 Myxophyceae can survive, but at times these form 

 a heavy sludge over the bottom, where Chroococ- 

 cus turgidus, Gomphonphaeria aponina, Oscilla- 

 torias, and Lyngbyas dominate. If there is a 

 direct communication with the sea and some 

 circulation, if the area is relatively large, and 

 especially if there is a moderate depth of 3 to 12 



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