296 AQUATIC CLIMAX COMMUNITIES 



ered is the material carried in suspension in water. This includes 

 mineral matter, floating and swimming plants and animals, together 

 with dead bodies and parts and the feces of animals. A portion of 

 the detritus originates from pelagic and part from benthic organisms. 

 The amount of this is great, and it is often carried some distance from 

 its origin. However, the terrigenous material carried in suspension in 

 the sea is small in amount when compared with that of rivers, and on 

 the whole is less than in most lakes. It has been demonstrated that 

 lake waters are stained with brown coloring matter resulting from the 

 decomposition of vegetation (Pietenpol, 1918). A similar condition 

 undoubtedly exists in the sea, especially in coastal water (Knudsen, 

 1922). 



Light and Temperature. Radiant energy is transformed into heat 

 in water; essentially all the seasonal differences due to the sun's rela- 

 tive position are felt in waters as variations in light penetration and 

 heat. The climatic zones are, however, even less recognizable than on 

 land, owing to the high specific heat and general lag of a dense me- 

 dium. In shallow water, differences in temperature, light, etc., are 

 great in proportion to differences in depth. In deep water, however, 

 the reverse is true, variations in temperature being small, but animals 

 proportionately more sensitive. All the swimming and floating objects 

 obstruct radiant energy and thereby heat. They also affect light in- 

 tensity in proportion to their abundance, and at the same time the 

 penetration of various wave lengths is a function of their selective 

 absorption. Through the obstruction of radiant energy, the pelagic 

 community, including plankton, produces a reaction similar in some 

 respects to the shade cast by an open leafy canopy (Shelford and Gail, 

 1922; Shelford, 1929, b; Williams, 1929; Oster and Clark, 1934). De- 

 tritus and terrigenous matter are comparable in some respects to 

 dust in the air (cf. Humphreys, 1920). 



Dissolved Substances. Another striking difference between air and 

 water is the marked variation in solutes from point to point in the 

 latter, especially the products of metabolism and of decomposition of 

 organic matter. Dissoh'ed oxygen is an important feature of hydro- 

 climates, largely because of the variation in amount. Birge and Juday 

 (1911) have considered it in detail for glacial lakes, and the horizontal 

 and vertical distribution in the Atlantic has been outlined by Murray 

 and Hjort (1912:255-256). Its consumption is primarily affected by 

 the respiration of living organisms, and especially the decay of dead 

 bodies. It is added to the water by chlorophyll-bearing organisms 

 only near the surface and during the day. The open waters of Wash- 

 ington Sound always show a deficiency of at least 1-2 cc. per liter as 



