244 w - c - ALLEE. 



sewage wastes, so this possible factor in distribution may be 

 dismissed. 



The effects of tidal currents are well illustrated in the gutters 

 and creeks of Hadley Harbor. These protected channels, sup- 

 plied with constantly changing water which differs from open 

 water only by the effect of coming over large tracts of submerged 

 vegetation, support a wholly different animal life from that 

 present where such currents do not enter. These locations are 

 in the exposed rock or the rock-rockweed stage of development, 

 in place of the Mya or Melampus stage which they would occupy 

 if the currents were absent. In addition to these scouring effects 

 of tidal currents, they have the well known function of oxygen 

 and food carriers. They also eliminate the depth gradients in 

 oxygen and pH found commonly in the stagnant water of the 

 older associations. 



The relation of oxygen and pH of the sea water to animal 

 distribution has received no attention in the Woods Hole region. 

 Both depend (i) on the supply of offshore water, (2) the amount 

 of photosynthesis being carried on nearby, and (3) the character 

 of the bottom. In the open water these factors depend upon 

 currents and the proximity to vegetation. In the presence of 

 vegetation oxygen is given off and the pH is increased. Muck 

 absorbs oxygen and lowers the pH while sand has no effect on 

 either unless it has been laid bare, when it, as well as rocks under 

 similar conditions, decreases the pH without affecting the 

 oxygen supply. Wave action has the converse effect. 



From examining data from such regions as the rockweed or 

 eel grass one might be tempted to generalize and say that as the 

 oxygen increases the pH likewise increases and vice versa. Such 

 a conclusion at best holds only in regions of abundant vegetation 

 or of muck, and there the pH changes lag behind changes in 

 oxygen concentration. 



If the invertebrates are as sensitive to pH variations as Powers 

 found herring to be, this correlation of high hydrogen ion con- 

 centration with the low oxygen regions of the muck must serve 

 to keep free moving animals out of such conditions. Such 

 action, combined with its greater regularity of distribution and 

 slower fluctuations, makes the pH of the water more important 



