consisted of many Lycosoma, some half-digested, 

 and of Skeletonema, which was also abundant 

 among the branches. It is apparent that some 

 constituents of the periphyton may be mgested 

 and that the microscopic flora of the envu-onment 

 provides a substantial amount of food not avail- 

 able in true phytoplankton. 



Some of the seaweeds cause unexpected damage 

 to commercial oyster grounds. Colpoinenia sinu- 

 osa (Toth) Derbes and Solier, a common seaweed 

 in many parts of the word, is one of them. It 

 grows along the Pacific Coast of North America 

 from Alaska to southern California, along the 

 eastern coast of Australia and in France. The 

 thallus of Colpomenia is of a papery texture and 

 hollow; it can grow attached to oyster shells to 

 the size of a hen's egg or tennis ball. On sunny 

 days at low tide in shallow water photosynthesis 

 may be so intense that gas bubbles fiU up the 

 thallus, and on the return of the tide the inflated 

 balloon floats out to sea carrying with it the young 

 oysters. In 1906 Colpomenia became such a 

 nuisance on the western coast of France at Vannes 

 that the oystermen called it "oyster thief." The 

 floating oysters carried out by the ebb current 



were not returned to shore with flood tide, and 

 the losses were severe enough for local oystermen 

 to organize the recapture of oysters with nets and 

 to tear off the inflated algal ballons by dragging 

 faggots over the bottom (Church, 1919). 



In 1961 the seaweed, Codium Jragile subsp. 

 tomentosoides (Goor) Silva, was introduced to 

 Cape Cod waters with oysters brought from 

 Peconic Bay, Long Island, N.Y. This Pacific 

 Ocean species, not indigenous to Massachusetts, 

 occurs in abundance along the western coast of 

 Europe. It is not known how the alga was 

 introduced to Long Island where in January 1957 

 it was found at East Marion attached to dead 

 Crepidula shells (Bouck and Morgan, 1957). In 

 Oyster River, near Chatham, Mass., where the 

 Long Island oysters were planted the shells were 

 covered with a luxuriant growth and had to be 

 thoroughly scrubbed before being shipped to 

 market. The following year the plants were so 

 large (fig. 388) that on sunny days they acted as 

 "oyster thieves" by lifting the oysters from the 

 bottom with gas-fiUed branches and floating them 

 off with the tide. 



Eel grass, Zosfera marina, frequently covers the 



Figure 388. — C. fragile introduced into Oyster River, Chatham, Mass., with oysters from Long Island. Two-year-old 



plant. 



FACTORS AFFECTING OYSTER POPULATIONS 429 



733-851 O — 64 28 



