STUDIES IN MARINE ECOLOGY. 



209 



finding temperatures from some depth below the surface. All 

 determinations were ordinarily made in duplicate and, oxygen 

 excepted, frequently in triplicate. 



Table I. 



Showing Comparative Results of Using Three Indicators in 

 Determining the pH of Sea Water. 



III. Series of Associations. 



The animal associations of the Woods Hole littoral can be 

 divided into two series either on the basis of the character of the 

 bottom, or of physiographic action. On either .basis the resulting 

 series are the same, for the eroding shores of the region are all 

 rocky and the depositing shores have a shifting bottom composed 

 of mud or sand. Within these series the associations may 

 readily be arranged in the order of their physiographic age. 



The associations of the rocky eroding shores as studied are: 



(1) open water; (2) wharf pilings; (3) exposed rocks; (4) pro- 

 tected rocks. The associations of the depositing shores likewise 

 begin with (1) the open water and typically continue as follows: 



(2) those of the sand bar; (3) with the deposition of mud this 

 becomes the muddy sand association in which eel grass begins; 

 (4) with further deposition of mud and as the eel grass grows 

 longer one finds the Cumingia association and in deeper water 

 where still more muck has been deposited, the Scoloplos acutus 

 association. These make up the two main associations of the 

 eel grass and muck, which extend to the margin of the eel grass 

 in about a foot of water at low tide. Between this level and the 

 shore at about low tide lies the marginal muck association (5) 

 which gradually gives way to the intertidal associations, the 

 lower of which may be called the Mya association and occupies 

 the region from just below low tide to about the half tide mark. 

 The upper association is marked by the abundance of the snail 

 Melampus and may well be called by that name. In places the 

 Ucas are more abundant, but such localities have not been 

 studied in this report. 



