COMMUNITY ORGANIZATION: STRATIFICATION 449 



forms tend to occupy higher strata where major community at the self-sustaining level 



there is sufficient Ught for photosynthesis, in which the upper stratum would be 



If this is tlie correct explanation, it af- ecologically comparable to the deciduous 



fords a striking illustration of the biological forest canopy and the sea floor comparable 



effect, by the whole plankton, on tlie verti- to the floor of such a forest, 

 cal arrangements of its constituents, with Klugh and Martin (1927) checked the 



the chlorophyll-bearers reacting primarily p;rowth rate of marine algae against depth 



to the hght gradient and secondarily to jf submergence. The algae were found to 



population pressure. have a specific stratum at which they grew 



These shade species of Ceratium have more rapidly; this increase in growth rate 



their cells thin-walled and crowded with was attributed to adjustments to different 



chromatophores, in contrast with the sun amounts of light. Summarizing their data: 



species. Nielsen compared these shade spe- ScijtosipJwn lomentarius grew more rapidly 



cies with the shade plants of the tropical at 1 meter, Ectocarpus ccnfervoides and 



rain forest which inhabit lower strata of the Enteromorplia linza at 2 meters, while 



forest community and which have the leaf Fucus vesiculosiis grew more rapidly when 



surface increased, the leaf thin, and have just submerged beneath the surface, 

 an increase in the number of assimilating Lastly, this distribution of algae with 



cells. respect to light can be shown by direct 



Graham (1941), using the extensive field methods. Working in the compara- 



Ceratium collections of the Carnegie from tively shallow waters of Puget Sound, Shel- 

 the North Atlantic, North Pacific, and 



South Pacific, presents an analysis of this Table 32. Vertical Distribution of Light In- 

 genus in relation to the environmental in- tensity in Puget Sound (After Shelford 



fluences. His data check and ampUfy the ""^ ^^^^' ^^^^^ 



general conclusions of Nielsen as to verti- Depth in Meters Light Intensity 



cal distribution. Thus, Graham studied in Foot-Candles 



fifty-eight species of Ceratium, and of Above surface 8650 



these twenty were shade species and At Surface 6550 



showed an increase in frequency from sea 1 5400 



surface to the 100 meter fine. | ^^^jj 



Within the range of a group there is usu- . 9=^00 



ally a specific distribution pattern, as shown e 1990 



by the various species of Ceratium in the q X52o 



upper portion of the photic zone. For ex- 7 1397 



ample, within the prawns, Acanthephyra 8 1190 



purpurea is fairly abundant from 1000 9 990 



to 2000 meters, reaching maximal day- ^^ °^0 



time density between 1200 and 1400 ^^ ^^^ 



meters; Systellaspis debilis has the same en 109 



range, but reaches a daytime maximal den- 75 74 



sity at 100 meters; Hymenodora gracilis loo 38* 



becomes increasingly abundant downwards, 120 14 



reaching a maximal daytime density at 



2000 meters * Many plankters, the "shade species," in the 



rrni 1 '. . . r ., XT ii A j^i ^- opeH oceaH reach their general limit at the 



The pelagic strata of the North Atlantic ^^^ ^^^^^^ j^^^ j^^ light intensity, about 38 



discussed here have been treated as biomes foot-candles, in the littoral zone is about the 



by Clements and Shelford (1939, pp. 317- average intensity for the floor stratum of north 



320). This is not tenable if by such treat- temperate mature deciduous or evergreen 



ment these authors suggest that each of forests at noon in midsummer, as well as the 



these strata is equivalent to the grassland Aoor of tropical rain forests at midday. It is 



or the deciduous forest biome. Pelagic ^^"'^"§ ^° T*^ J^* f ^^^. *^!j|g^,* ^P^^^l^* 



1 J. . . J J ii 1 .. 1 1 33 root-candles { Smithsonian Tables for 1918), 



subdivisions depend upon the phytoplank- ^^ ^^^^ ^^^ ^^ ^^ ..^^^^^„ ^^ "tonight" 



ton of the upper few hundred meters for ^^^i^ appear to be fairly unanimous for 



their food. This means that they form in- Ceratium, Homo, and a motley array of 



terdependent portions of a vast marine silvicoles. 



