Chapter II.— SOME FACTORS AFFECTING THE DISTRIBUTION OF ALG/E AT 



WOODS HOLE AND VICINITY. 



I. THE COAST. 



The shore line of Woods Hole, of the Elizabeth Islands, and of neighboring regions 

 along Vineyard Sound and Buzzards Bay is in some respects remarkably varied (see 

 chart 225), but lacks certain important physical features present in other localities. 

 The coast, wherever exposed to wave action or tide currents, is composed of bowlders 

 and stones or consists of sandy and stony beaches. This is because the bowlders and 

 stones have remained at the shore line as the finer material of the glacial deposits covering 

 this region was washed away by the erosion of the coast. The sheltered coves, bays, 

 and harbors will generally have a sandy or muddy shore, sometimes gravelly, with scat- 

 tered groups of stones or bowlders. There are also small salt marshes connected with 

 some of the coves, as at Quisset and Hadley Harbor. There are no outcroppings of 

 rock, except in the vicinity of New Bedford Harbor, to make possible perpendicular 

 or slanting ledges and rock pools. An account of the geography of the region, together 

 with the character of the shores, is given in section i, chapter 11, pages 28 and 29. 



For the reasons stated above one misses some of the very characteristic associa- 

 tions of algae which may be noted in tide pools and along the sides of rock masses where 

 there is opportunity for the development of conspicuous bands or zones of vegetation 

 between tide marks and below — associations that are well illustrated in such localities 

 as Newport and at Nahant, near Boston. A shore of bowlders presents a broken line 

 at the water's edge which can not show to full advantage the distribution of algae in 

 zones. There are good illustrations of zonation in places, but they are on a comparatively 

 small scale and become evident only as groups of rocks or parts of the shore are studied 

 in detail, as was done for Spindle Rocks in the harbor of Woods Hole, to be described 

 later (pages 476-479) . Another factor that works against the conspicuous zonation 

 of algae in this region is the relatively small tide, which does not give much opportunity 

 for the development of broad zones of differentiated algal growth. 



2. THE BOTTOM IN DEEPER WATER. 



As would be expected in an area of glacial drift, the bottom offshore and in the 

 deeper portions of Buzzards Bay and Vineyard Sound may consist of sand, gravel, or 

 stones, with or without deposits of mud, but is frequently of a more or less mixed or 

 spotted character. Channels swept by swift tides are likely to be stony and sandv, 

 while sheltered coves, bays, or other regions, free from the scouring action of tidal 

 currents, usually have a muddy bottom. The ledges or other areas composed of bowl- 

 ders are simply pi'°s of stones heaped together where they were laid after the finer 

 matrix of the glacial drift had been washed away. The muddy bottoms are due to 

 deposits of silt where the water is sufficiently quiet because of its depth, or because of 

 the absence of tidal currents or wave action sufficiently strong to prevent the accumu- 



445 



