MARINE ALGAE OF NHATRANG BAY, VIETNAM 491 



are found. Conversely, except for a few cosmopolitan species, very few 

 occur whose ranges extend into temperate climates. 



In contrast, only three miles from the Institut is an intertidal lo- 

 cality of markedly divergent ecology and distinctive flora. A short sea 

 wall and associated small area of rough rocks is exposed to the open 

 South China Sea through the broad entrance to Nhatrang Bay, and is 

 subject to heavy surf. This violently agitated locality is densely vege- 

 tated with about 25 species of green and red algae. (Phaeophyta were 

 essentially absent). Of these, all but four species, of which three are 

 cosmopolitan, were not found elsewhere in the Nhatrang area. Fur- 

 thermore, most of the dominant species are of special distributional 

 interest. Of the four most abundant and luxuriant species, all of the 

 genera Gymnogongrus and Grateloupia, three are characteristic of south- 

 ern Japan. Also present and of northern distribution centering in 

 southern Japan are Porphyra crispata and Gymnogongrus japonicus. 

 Another dominant species was Cladophora perpusilla which is hitherto 

 known only from equally high southern latitudes at the Juan Fernandez 

 Islands. 



The occurrence of this assemblage of species characteristically in- 

 habiting the cooler waters of latitudes higher than 30° seems clearly to 

 reflect the importance of violent agitation in counteracting the lati- 

 tudinal effects of warming. Thus, the effect of the surf in increasing the 

 amounts of carbon dioxide and oxygen available to the plants appears 

 to compensate for the lower solubilities due to warming. 



Another locality of more than ordinaiy interest in Nhatrang Bay 

 is an exposed ryolite rock about 25 yards in extent lying in the entrance 

 to the bay. It is awash at high tide and subject to constant surge. Its 

 algal flora consists of about 17 species of which all but three were found 

 in no other place in the Nhatrang region. The dominant plants were 

 Chnoospora pacifica, Dermonema frappieri, Chaetomorpha antennina 

 and Ectocarpus breviarticulatus, all of which are of more or less wide, 

 but discontinuous tropical distribution, being characteristic of just such 

 exposed, surge-swept habitats as obtain on this rock. Such species as 

 Gigartina intermedia and Laurencia tenera represent a northern com- 

 ponent in this flora, while Ceramium taylorii of Pacific Mexico and 

 Mesothamnion caribaeum of the Caribbean add an interesting but un- 

 explained exotic element. 



At this point it should be made clear that the collections at hand 

 represent only the winter flora occuring from January to mid-March. 

 During this season the surface temperatures in Nhatrang Bay range 

 relatively low, from 24° to 26°, compared to the average surface tem- 

 perature for this north latitude in the Pacific and Indian Oceans which 



