PROCEEDINGS OF THE ACADEMY OF 



[June, 



irudis 

 palliata 

 liltorea. 



V 



Young Gull 



Chemical compounds. 

 . dissolved in sea water 



'hyxorplanktor 



oo-plankton 



'Balanus 



ult Gulls 



(Pollack and cunner) 



Fig. 



1. — Diagram illustrating the principal relations of Thais to its organic 

 environment in the Rock Association. To be complete this diagram should 

 show an entire cycle of the material. Each one of the organisms listed 

 above gives off liquids to the sea water that may be again used. They also 

 furnish solids either as waste products or by death, which, when acted on 

 by bacteria, will give more soluble matter as well as a residual solid that 

 will help contribute to the sea bottom in other localities. The dead animals 

 will supply food for amphipods, the amphipods food for fishes like the 

 sculpin, and so relations are established with other associations. This 

 diagram shows that the biota of the Rock Association is dependent alone 

 on the palagic formation. The relationships with other associations are 

 destructive to it rather than constructive. 



The young snail has enemies in the shape of fish, so those which 

 fail to take refuge in small cracks in the rocks are destroyed. At 

 this time the food consists of young mussels which grow abundantly 

 in the joints in the rocks. If one does not know where to look for 

 the young snails, none will be seen, so far are they crowded into the 

 cracks. 



A few pollack that were caught at high water over a Thais 

 habitat had their stomachs full of young Littorina palliata which 

 they had eaten from the same locality in which Thais lives. L. 

 palliata cannot hide in the rock cracks, as their food is on the Fucus 

 stems. If the fish could find young Thais, there is no reason why 

 they should not be eaten as well as Littorina. 



Although the young snails are hatching throughout the greater 

 part of the summer, most of them hatch out in August and reach 

 between 10-15 mm. in the first winter. This is measured by large 

 ridges on the shell, which indicate periods of rest in the growth of 

 the shell. These rest periods are assumed to indicate the winter, 

 but are not proved to correspond to it. 



