472 BULLETIN OF THE BUREAU OF FISHERIES. 



covering the years 1902-1906), passes 6o° F. about June 1, holds between 69 and 71 

 from about July 11 to August 28, and passes 6o° in its, autumn decline about October 12. 

 The bottom temperatures were taken at a large number of stations in both the Bay and 

 the Sound during the month of August. They were at this time highest in the upper 

 portion of Buzzards Bay, where 71. 3 was recorded, while in Vineyard Sound 68.8° was 

 recorded off Falmouth, and 66.9 off the west end of the Middle Ground, these temper- 

 atures becoming in general lower toward the mouth of Buzzards Bay and the westerly 

 portion of Vineyard Sound. The warm-water sublittoral formation may, then, be said 

 to endure a temperature of about 70 for midsummer, and its most favorable temper- 

 ature is perhaps close to 6o° or above, although many species live in colder water. It 

 would be very interesting to know to what degree the place of the warm-water sublittoral 

 is taken by representatives of the cool-water sublittoral as the temperature of the water 

 falls during the autumn. The cool-water sublittoral might be expected to invade the 

 narrow and easterly portion of Vineyard Sound and the upper portion of Buzzards Bay f 

 but we have no data on this problem. 



THE ZOSTERA FORMATION. 



There are a number of algse which have the habit of growing frequently or inva- 

 riably attached to Zostera. They, together with the eel grass itself, constitute a very 

 clearly defined assemblage which is here called the Zostera formation. It is really a 

 specialized region of the warm-water sublittoral formation, for the eel grass vegetates 

 during the summer when the water is warm. Many of the species listed below will 

 consequently be found in the lists of the latter formation (b). 



Zostera marina, the eel grass, is very abundant in all sheltered regions of both Bay 

 and Sound, forming thick beds in shallow waters. It was frequently found at inshore 

 stations of the survey, and also at scattered stations in deeper waters of the Bay and 

 Sound (chart 266), being dredged in 2 to 13 fathoms, over sandy, stony, and muddy 

 bottoms. The eel grass, however, prefers shallow water in coves and bays or along 

 sheltered coasts, where it grows luxuriantly, developing extensive beds in depths of 

 2 feet to 2 fathoms or more. Under these conditions the - formation described below 

 is frequently developed to a greater or less extent. Species preceded by the asterisk 

 are the most important forms; those which are rare or occasional are designated by (o). 



When the Zostera grows in very quiet and shallow waters the blue-green alga, 

 Anabcena torulosa, is common on the mud at the base of the plants, frequently breaking 

 loose and floating on the surface as slimy masses. Lyngbya majuscula sometimes forms 

 extensive tufted growths and, breaking free, also floats on the surface. Other blue- 

 green algse in the Lyngbya salt-marsh association (1) may be present. Hydrocoleum 

 glutinosum and Gloeocystis zostericola form coatings on the leaves, and Enteromorpha 

 clathrata, E. plumosa, with other species, and sometimes species of Cladophora, grow in 

 loosely attached masses. These algae are all forms which may be expected in brackish 

 water. 



When the eel grass grows in more open or exposed situations the list of epiphytes 

 includes species which are never found in brackish water. Among these the following 

 are conspicuous : 



