MARINE AIXJ^B OF BEAUFORT, N. C. 39! 



DISTRIBUTION OF ALG^E AT BEAUFORT. 



REGIONAL. 



The regional distribution of algae, their occurrence throughout the world, is, like 

 that of other plants, determined largely by temperature. Whether a given algal species 

 is able to exist in a given locality will depend absolutely on its ability to endure the 

 maximum and minimum water temperatures occurring in that locality. It need not, 

 however, be obliged to endure these extreme temperatures in its vegetative condition, 

 but may exist for long periods by means of spores or fragments, resuming its vegetative 

 state with the return of more favorable temperatures. Setchell (1915) has shown that 

 the majority of the species of algae occur in regions having a range of not more than 10 C., 

 and that those occurring in regions having a greater range than this accommodate them- 

 selves to the general law by their seasonal distribution, etc. 



Of the species which are able to exist in any given locality, some will thrive and will 

 predominate, others will barely maintain a foothold, while others will appear and 

 disappear at different times. The relative abundance of the different species occurring 

 in any locality will be determined by the ability of these species to thrive under the 

 conditions found there and to compete under these conditions with the other species 

 growing in the region. To become abundant, a species must be able not only to endure 

 the extreme conditions, but also to grow luxuriantly under the usual conditions. The 

 factors most affecting the relative abundance of the species of marine algae seem to be 

 the temperature, density, and turbidity of the water, and the intensity of the light 

 occurring, not on single days, but throughout the growing season. 



As has been mentioned, the intermediate position of Beaufort makes its flora 

 particularly interesting. Here Codium tomentosum, Dictyota dichotoma, Padina -vickersiaz, 

 and other strictly southern forms grow along with the more northern Fucus vesiculosus 

 and Polysiphonia harveyi. As a rule, however, the northern and southern species do 

 not grow together, the former occurring in the spring and the latter in summer. 



Setchell (1915), in considering the effect of temperature on the distribution of algae, 

 distinguishes the following regions, based on the average temperature of the water 

 during the summer expressed in degrees centigrade : 



'C. 



'C. 



South subtropical 20 to 25 



South temperate 15 to 20 



Lower austral 10 to 15 



Upper austral o to 10 



Upper boreal o to 10 



Lower boreal 10 to 15 



North temperate 15 to 20 



North subtropical 20 to 25 



Tropical 25 N. to 25 S. 



Since the average water temperature at Beaufort during the months from June to 

 September is 26.35 C., this classification would place the Beaufort area at the northern 

 limit of the tropical region. It would seem, however, that the Beaufort flora should 

 more properly be included in the subtropical region, and the limits given by Setchell 

 should be modified. 



SEASONAL. 



As is shown in Table i , the flora of spring and summer are very different. Of the 77 

 species and varieties growing in the harbor, only 15 (19.5 per cent) are found at both 

 seasons, 1 1 of these being perennial and 4 having been found from April to October. 



