A Community of Sea Mussels 



ONE OF THE GREATEST ORGANIZATIONS IN NATURE FOR MAKING FLESH 



FOOD BY A SHORT AND RAPID PROCESS AND IN PALATABILITY SEA 



MUSSELS RANK SECOND TO NO KNOWN SHELLFISH 



By IRVING A. FIELD 



Assistant Professor of Uiolofiy in Clark College, Worcester, Massachusetts 



VISITORS at the seashore are 

 often struck with wonder when 

 the receding tide exposes to 

 view vast areas of tlie sea bottom com- 

 pletely covered with mussels. The 

 favorite habitat of these clandike mol- 

 lusks is where the water is slightly 

 brackish, in shallow protected bays and 

 estuaries, on a l^ottom of mud rich in 

 diatoms and other microscopic plants 

 and covered more or less with stones or 

 other solid objects. The latter are 

 necessary to serve as a foundation to 

 which the mussels may attach them- 

 selves firmly by a series of strong 

 threads called the "byssus." These 

 threads not only bind the mussels to 

 foreign objects but also to one another, 

 so that it very often occurs that mem- 

 bers of a community are woven together 

 like a carpet. From such a bed it is 

 possible to tear loose extensive portions 

 and roll them up as one would a rug. 



Sea mussel beds may be encountered 

 along the seacoast almost anywhere in 

 the northern half of the Northern Hemi- 

 sphere. On our Atlantic coast they 

 occur in abundance in the shallow 

 sheltered bays along the coasts of New 

 Jersey, Long Island, Rhode Island and 

 Massachusetts. The beds thrive well 

 in shallow water where they are not 

 exposed long at low tide. They grow 

 much better, however, in the deeper 

 waters where they are not influenced by 

 extreme changes of temperature, frost or 

 ice. 



An interesting communitv of mussels 



which has been under my observation 

 for the past six years is in Menemsha 

 Pond on Martha's Mneyard, Massachu- 

 setts, not far from the famous Gay Head 

 Cliffs. The pond covers somewhat less 

 than a square mile and is connected 

 with Vineyard Sound by Menemsha 

 Creek, which is a broad deep channel 

 about half a mile long. This creek 

 allows the passage of a considerable 

 volume of water in a short time so that 

 the rise and fall of the water in the 

 pond between tides amounts to about 

 three feet. The density of the water 

 is very little less than that of pure sea 

 water, owing to the fact that very little 

 fresh water enters the pond. Much of 

 the bottom of the pond is muddy and 

 supports a luxuriant growth of eelgrass 

 {Zostcra marina). As the eelgrass dies 

 and disintegrates from year to year it 

 contributes to the organic matter of the 

 bottom and furnishes shelter and food 

 for myriads of microscopic plants and 

 animals, chiefly diatoms and Protozoa. 

 Where the pond converges into the 

 creek there is a great bar, ten acres or 

 more in extent, composed of mud, sand 

 and gravel, much of which is exposed 

 at extreme low tide. Over it the tidal 

 currents sweep vast quantities of micro- 

 scopic organisms, and fine particles of 

 dead organic matter derived from the 

 pond and from the open ocean. Seven 

 years ago this bar was a clam flat with 

 no mussels in the vicinity, but during 

 the following summer the tide carried 

 up Menemsha Creek billions of minute 



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