STUDIES IN MARINE ECOLOGY. 225 



2. Associations of Depositing Shores. 



Notwithstanding the slight amplitude of tides in the Woods 

 Hole region, there are a number of fairly extensive tidal flats 

 which furnish the basis for the associations of the depositing 

 shores. The best of these near the Laboratory is the flat opening 

 off Northwest Gutter just before it enters Buzzards Bay. The 

 majority of collections to be reported were made at this place. 

 Verification studies were carried on in Lackey's Bay, at Gansett, 

 and in Southwest Gutter Creek. 



The different animal habitats to be found on the flats grade 

 slowly from one to another so that it becomes impossible to get 

 hard and fast limiting lines. This is true even of the more 

 extensive flats, those at North Falmouth for example, but it is 

 particularly marked in regions such as Gansett where the water 

 deepens fairly rapidly, leaving only narrow zones along the 

 margin. Similar jumbling of habitats is to be found in the salt 

 water creeks of Hadley Harbor and is more characteristic of the 

 Woods Hole coasts than are the more gradual transitions found 

 on the flats proper. 



Theoretically the youngest stage in this series is that shown 

 in (a) the association of the open water. The conditions in such 

 positions have already been discussed so we shall proceed imme- 

 diately to the associations of the flats. 



b. The Sand Bar Association. — In this region tidal flats are 

 typically separated from the open water by sand bars which 

 may be much exposed at low spring tides, or just covered at low 

 neap tides. The outer part of the bar is relatively pure sand 

 which gradually becomes mixed with humus as one moves back 

 on the flats. The characteristic animals of such an association 

 are given in list 6. 



In places practically pure cultures of Scoloplos fragilis occur 

 in the sand and if an animal name for the association is desired 

 it might well be called the Scoloplos fragilis association. 



Where the sand bar extends out to the margin one finds the 

 expected evidences of vertical distribution depending on tide 

 level. At the upper tidal limit congregating under the eel grass 

 occur great numbers of the beach flea, Orchestia agilis; burrowing 

 in the sand are the Talorchestia longicornis and locally, Hippa 

 talpoida. 



