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EDGAR NELSON TRANSEAU 



nant. From the stand point of elevation this habitat might be 

 classified under the Lower Beach, for these creeks are usually well 

 above low tide. They owe their existence to the cutting off of a 

 lagoon by the building of a barrier. The lagoon sooner or later 

 develops into a salt marsh covered with water only at high tide. 

 The run-off of water during low tide leads to the maintenance of 

 these channels or creeks. Where the creek enters the sea there is 

 usually an area in which the substratum is almost continually in 

 motion. The tendency of the creek to form a bar across its mouth 

 by the deposition of materials held in suspension is opposed by 

 the waves and the shore currents. Upon the relative efficiency 

 of these agents depends the amount and the configuration of the 

 deposit. The agitation of the substratum is usually sufficient to 

 prevent the growth of vegetation. Consequently there is a mini- 

 mum of vegetation at the debouchure. The amount and variety 

 increase as we go up the creek until a point is reached where the 

 Zoster a completely fills the channel. Here the conditions are not 

 so favorable for the algal constituents and they decrease rapidly 

 in number. The presence of a large number of red algae is prob- 

 ably to be correlated with the perfect aeration of the water. When 

 the tide rises the water which flows inward is fresh from the Sound 

 or outer harbor. When it falls the water which has been spread 

 out in a thin layer over the marsh rushes out with a current suffi- 

 cient to afford rapid change. During low tide the light conditions 

 are nearly the same as above the water level. It was noted in 

 this connection however that where the red algae attained their 

 best development the creek was shaded b}' high banks or by the 

 adjoining growth of Spartina cynosuroides. 



The Dasya Association. At the mouth of the creek on Cen- 

 ter Island, outside the bar, scattered specimens of Dasya elegans, 

 Grinnellia americana, Griffithsia bornetiana, and Callithamnion 

 americanum occur attached to the sandy bottom. A short dis- 

 tance up the creek from its mouth where rocks afford a stable 

 foothold Ulva laduca, Enteromorpha clathrata, E. intestinalis, and 

 Ceramium rubrum appear. Zostera appears first on the concave 

 side of the curving channel where the water is shallowest and 

 the current weakest. At first it supports an abundant growth 

 of Melosira. Then Ceramium rubrum, C. strictum, and Entero- 



