382 Pnh. Puget Sound Biol. Sta. Vol. 2, No. 54 



place. The range perhaps varies for different species of animals. Mc- 

 Clendon (1918) claims that there is no optimmn pH for plants but that 

 the range of pH compatible with the life of sea weeds is rather broad and 

 may be different for different species. The foregoing observations show 

 that the range of the pH differs markedly for different habitats or rather 

 different classes of habitats. The fixed plants and the animals of this 

 plant habitat, unless they have a diurnal migration, must tolerate large 

 and sometimes very rapid changes of the pH every 24 hours, at any rate^ 

 during the most vigorous growing season of the plants. Perhaps the ani- 

 mals that have to tolerate the greatest as well as the most rapid change 

 in both the pH and the oxygen content of the water are those which 

 live in burrows among the Ulva above low tide level. P'or example, whea 

 the tide comes in, the first water that comes in contact with Upogebia 

 pugeteii^is, which is bathed with water perhaps with as low a pH as 7.22 

 and oxygen content of 0.15 cc. per liter, may have a pH as high as 9.3 

 and be supersaturated with oxygen. Or the change in pH may be as 

 great as 1.98, and in oxygen content sufficient in itself to supersaturate 

 the water. However, the rapidity with which these changes take place can 

 be controlled largely by the burrow-living animals. Tht; animals of the 

 open water or the plankton do not have to tolerate such great variations 

 in i^H and oxj'gen content. Bethe (1909) found that the rhythmic move- 

 ments of medusae are hastened if the reaction of the water is changed 

 from a Ch of 10"^ to 10"' or 10"'"', while a concentration of 10"" or 10"^ 

 will diminish or paralyze the movements. McClendon (1916) found that 

 all marine animals tested by him died more quickly if the pH was changed 

 beyond the limits of 6 to 8.25. Tlie oxygen consumption of certain marine 

 invertebrates is known to vary with the pH (McClendon 1917) and the 

 oxygen tension (Moore, Roaf and Whitley 1905, Henze 1910. I.oeb and 

 Wasteneys 1911, McClendon 1917b and 1918, and others). While an 

 exhaustive study has not been made of the fauna of the Puget Sound 

 region by the writer, the luxuriance of the fauna at certain localities, and 

 the comparative average sizes of individuals of the same species, as for 

 example the barnacles at different localities, seem to suggest that the 

 specific pH range has more to do with the compatability of their habitat 

 than other factors such as the oxygen content of the water. This needs 

 further investigation. The foregoing observations also suggest that Puget 

 Sound and similar regions are ideal natural laboratories for the study of 

 the causes of vertical migrations of plankton organisms. Here are found 

 natural variations in the relations of light, carbon dioxide and oxygen 

 tensions of the water without the objections used as argument against 

 purely laboratory observations. 



