Spirochaetes 



Tissues of oysters are often infected by spiro- 

 chaetes which may be found in the stomach, 

 crystalline style sac and in the gonads after 

 spawning. Dimitroff (1926) identified 10 species 

 and found that 91 percent of the oysters sold in 

 Baltimore, Md. were infected. He reported the 

 following species: Saprospira grandis Gross; S. 

 lepta, S. puricfa; Crisiispira balbiani (Certes); (". 

 anodontae Keysselitz; C. spicuUJera Schellack; (\ 

 modiola Schellack; 0. mina; C. tena; and Spirillum 

 ostrae Noguchi. The species are harmless to 

 oysters and man. 



Perforating algae 



The empty shells of oysters and other mollusks 

 found on tidal flats and on the bottom are fre- 

 quently perforated by various algae. Bornet and 

 Flahault (1889) gave a detailed description and 

 illustrations of several species, some of them also 

 found in the carapaces of crabs. Ijive mollusks 

 do not escape the attacks of perforating algae. 

 0. edulis of \'arious ages living in the channel of 

 Saline de Cagliari, Italy, were found to be infested 

 by three species: Hyella caespitosa Bornet and 

 Flahault; Mastigocoleuv testarum Lagerheim; and 

 Gomontia polyrrhiza (Lagerheim) (Agostini, 1929). 

 The algae penetrate the periostracum, then spread 

 across the prismatic layer, and form branching 

 threads in the inner layer of shell. Apparently 

 the gi-owing tips of the filaments dissolve the 

 calcium carbonate of the shell and make possible 

 the expansion of algae which, in severe cases of 

 infestation, spread through the entu'e valve and 

 become noticeable by the gi-eenish color of the 

 valve's inner surface. The color cannot be rubbed 

 off the surface since the alga is separated from the 

 oyster and does not come in du-ect contact with 

 its body. The algal filaments can be studied on 

 fragments of shell or after decalcification in acid. 



Gomontia polyrrhiza, continuously distributed 

 along the Atlantic coast, has been reported from 

 North Carolina and Connecticut, to New Bruns- 

 wick, Canada, growing in empty shells along the 

 shores and occasionally found in live Spirorbis 

 and barnacles (Taylor, 19.37). 



Live oysters infested \vith perforating algae are 

 occasionally found in shallow bays and estuaries 

 of Cape Cod. The inner surfaces of the valves 

 are bluish-gi-een. At Woods Hole I saw under a 

 microscope a network of perforating algae re- 

 sembling Gomontia and probably mi.xed with other 



species. The plants have not been positively 

 identified. 



Perforating algae do not appear to be harmful 

 ro oysters. Continuous growth in empty shells 

 accelerates the disintegi-ation of the shells and 

 the return of calcium salts to the sea. 

 Fouling organisms 



Many sedentary marine organisms use oyster 

 shells as a convenient place to attach, either per- 

 manently or temporarily. They do not penetrate 

 the shell nor do they inflict any direct injury on 

 the oyster, but they do compete with it for food 

 and space and sometimes smother the oyster by 

 their accumulated mass. The most conspicuous 

 among them is the American species of slipper 

 shell, Crepidula fornicata (L.), which received in- 

 ternational notoriety because of the havoc it 

 caused for oyster growers in Europe. 



Various species of Crepidula are very conunon 

 gastropods found attached to hard objects near 

 or below low water. C. fornicata does not present 

 a problem to oyster gi'owcrs in the United States, 

 although sometimes in certain estuaries, as in 

 Cotuit Bay, Mass., it becomes a nuisance because 

 of its extraordinary abundance. .Slipper shells 

 settle on oyster shells and tend to form a spirally 

 curved chain of individuals, the sexes of which 

 change from female to male (fig. 386). 



The lowest and, therefore, the oldest members 

 of the chain are always females. The uppermost 

 are males, and those between the two extremes 

 are hermaphrodites, which undergo changes from 

 female to male. To the biologist the species is of 

 mterest because the alteration of sex which takes 

 place in this mollusk offers an excellent opportu- 

 nity for experimentation. Grounds heavily in- 

 fested with Crepidula are, tlierefore, of great value 

 as a source of material for marine biological lab- 

 oratories. Oyster growers do not share this en- 

 thusiasm because the presence of large numbers 

 of unwanted slipper shells requires additional 

 work in cleaning the oysters before delivery to 

 market. 



On many occasions C. fornicata has been intro- 

 duced to Europe witli the sliipment of live oysters 

 from the United States. It has established itself 

 in Essex, Northumberland, Falmouth, England, 

 and in Soutli Wales. In 1929 the first specimens 

 of C. fornicata were noticed in the Oosterschelde, 

 Netherlands, and in 1932 to 1933, according to 

 Korringa (1950), the situation became alarming. 

 The mollusk spread to the German and Dutcli 



426 



FISH AND WILDLIFE SERVICE 



