GULF OF MEXICO 



185 



B. binderi, more or less intermixed with Entero- 

 morpha (fig. 48-c) and Rkizoclonium. Green turfs 

 of Cladophoropsis membranacea and darker ones 

 of Cladophora f'uliginosa may be close by, with 

 mats of Wiirdemannia miniata and closer-attached 

 Gelidium pusUlum, but Catenella and Caloglossa 

 are less important than in localities discussed 

 earlier. Seasonal growths of Colpomenm sinuosa 

 (fig. 49-d), Hydroclathrus clathratus and perhaps 

 Codium intertextum are to be expected near the low- 

 tide line, with Laurencia papillosa and Sphacelaria, 

 stunted Sargassum, Amphiroa, and Centroceras. 



At levels primarily submerged or laid bare only 

 bj* the backwash of the waves, we have a richer 

 and sometimes spectacular vegetation. Near the 

 surface a new group of Chlorophyceae appear: 

 CauJerpa racemosa and C. verticillata, C. sertu- 

 larioides, C. cupressoides, Dictyosphaeria cavernosa. 

 and Dasycladv^ vermicidaris on the rock faces, 

 Anadyomene stellata and Valonia macrophysa more 

 in crevices or other protected spots. We also 

 have such Phaeophyceae as Ectocarpus duchas- 

 saignianus, Pocockiella variegata, and Dictyotas. 

 Somewhat deeper, we may have the brilliant 

 peacock colors of great masses of Zonaria zonalis, 

 and at this level, abundant Padinas, Sargassums, 

 Cladophora Jasciculari^iHg. 48-b),and more Dictyo- 

 tas, among which D. cervicornis (fig. 49-a), may be 

 the most common, but D. ciliolata and D. dentata 

 will reach the greatest size and are often irridescent. 

 Here, also, come a few species of conspicuous 

 Rhodophyceae, Galaxauras, and Liagoras, with 

 lower down Heterosiphonia wurdemanni, Centro- 

 ceras, and Spyridia in masses, and some showy 

 Halymenias. The number of other kinds at this 

 and nearby levels makes continued detailed 

 listing unprofitable. 



PELAGIC SEAWEEDS 



The fact that the term "gulf weed" for our drift- 

 ing algae has arisen at all is suggestive of the 

 conspicuousness of these plants in our area. 

 Although the term has long been known, one has 

 come to think of these plants more in relation to 

 an ill-defined "Sargasso-Sea" in the North Atlantic. 

 However, while the abundance of the "weed" in 

 the Sargasso Sea is perhaps greater than in the 

 Gulf of Mexico, the amount is nevertheless con- 

 siderable in the northwestern parts even if less 

 conspicuous in the literatxu"e. The best general 

 account of the distribution and ecology of the 



gulf weeds is that of Parr (1939), and it particularly 

 deals with Sargassum as found in the Gulf. The 

 taxonomic segregation of the Gulf and the Carib- 

 bean benthonic and pelagic species is far less 

 difficult than that of the Pacific species but still 

 is exceedingly confusing to an inexperienced 

 student of them. The books mentioned for the 

 general flora will clear up most points; the sum- 

 maries of information regarding the species of the 

 world in DeToni (1895) and Grunow (1915-16) 

 will be necessary to the advanced student. 



First of all, it is to be recognized that the 

 benthonic sargassums are particularly suited to 

 transport by currents once they come adrift, and 

 any such species may travel among the driftweeds 

 for a long distance from their origin. Thus, 

 Sargassum hystrix v. buxijolium has been collected 

 on the coast of Nantucket among gulfweeds as 

 a very exceptional occurrence (1938, for example). 

 However, the new growth on these plants is not 

 so altered from the parts developed during the 

 attached growth period as to resemble the pelagic 

 species. Of these, there are two: The classic 

 Sargassum natans (L.) J. Meyen (fig. 50-a) and 

 S. fluitans B0rg., each somewhat variable. How- 

 ever, the former has much narrower leaves with 

 more terete teeth than the latter, and the vesicles 

 are characteristically long-apiculate. While the 

 leaves of S. natans never have cryptostomata, 

 rudiments of them may occasionally be seen in 

 the latter species. Neither has been convincingly 

 reported in fruit, contrary to the common state 

 of mature benthonic plants. Parr (1939) re- 

 ports that significant amounts of drifting gulfweed 

 are not found south of a line extending from 

 approximately the latitude of 16°-17° near the 

 Lesser Antilles to 14° near the Central American 

 coast. We may accept it that there is very rapid 

 growth and fragmentation of the floating plants 

 north of this line, and there is no evidence that 

 the pelagic flora needs to be initiated by a con- 

 stantly replenished nucleus of benthonic origin. 

 Both species of gulfweed, passing out thi-ough the 

 Straits of Florida, continue in excellent health 

 into the drift area called the "Sargasso Sea" and 

 multiply vegetatively there. The wind and the 

 water currents also bring the sargassums into the 

 Gulf of Mexico. While there seems to be some 

 growth of the plants within the Gulf, especially 

 during the summer, it is clear that it is not very 

 considerable, and the flora comes to consist of 



