6 The Animal Ecology of the Cold Spring Sand Spit 



i. fauna of the submerged zone 



The animals that live below the high-tide line may be considered under four 

 heads : (a) sessile species, (6) crawling species, (c) burrowing species, and (d) swim- 

 ming species. 



a. The sessile species of animals, inhabiting the lower beach, include certain 

 molluscs, especially bivalves, or Lamellibranchiata. All the lamellibranchs feed on 

 minute particles of organic matter : Algae, Infusoria, and decaying bits of organisms. 



Fig. 4. — Photograph of lower beach, north side of sand spit, near the eastern end, at very low tide. The gut is 

 seen in the background. At the water's edge (submerged zone) is a dense growth of the alga Enteromorpha. The naked 

 lower beach is thickly peopled with the mud snail, Nassa obsoleta, visible as dots in the photograph. 



The silt brought down by the creek is rich in such material and the algae thrive on 

 the mud flats, consequently these flats and the shallow sea around the flats are espe- 

 cially favorable feeding-grounds for these molluscs. Here occur oysters (Ostrea vir- 

 giniana) in a semi-domesticated state. They normally attach themselves to some solid 

 object while still young, but those of Cold Spring Harbor have been mostly trans- 

 planted and lie loose in the shallow waters, but altogether incapable of movement or 

 of any other defense than that provided by their two thick valves. Here also occurs 

 the scallop (Pecten irradians), which attaches itself while yet less than two weeks old, 

 in the middle of August. The attachment is chiefly to eel-grass or to small stones. 

 About the middle of September the scallops migrate into the inner harbor to live on 



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