MARINE ALG OF BEAUFORT, N. C. 391 
DISTRIBUTION OF ALGA AT BEAUFORT. 
REGIONAL. 
The regional distribution of alge, 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 alge 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 algee 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 Codiuwm tomentosum, Dictyota dichotoma, Padina vickersia, 
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 alge, 
distinguishes the following regions, based on the average temperature of the water 
during the summer expressed in degrees centigrade: 
Lipperisboreal sp aicsi- Fyn shrewd oraryetia- 4 o to 10 | South subtropical. ..............0000000s 20 to 25 
Lower horeal ss. 26/02. 50 |. gras tesa s+ To to.r5 | \So1thtemperates vo ose. csiers sisjasogte =~ 15 to 20 
North temperate yet core cies og cise vis eke De tO zon LOWER AUSIR A cc mace ec eaericleltoemay ond eer to to 15 
INGIiLSMULOpICdl ener arc et crea ices BOWOTAG | MUPPEL AUS AL yc cents oo eaten ee isteisiete ts o to Io 
Tropical’; 212 SIQEL i. Dah. ee 25 N.to25S. 
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 1, 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, 11 of these being perennial and 4 having been found from April to October. 
