disease on mussel populations is that of the 

 invasion of the north European sea mussel 

 stocks by the copepod Mytilicola iiifestiiialis. 

 A fascinating body of literature has accumu- 

 lated about this parasite and its ofYocts on 

 mussels; only a sampling- of the many published 

 papers is cited here. Steuer (1902) first de- 

 scribed the parasite from the intestines of 

 Mediterranean edible mussels, :ind Pesta (1907) 

 outlined the life history. Korringa (1950, 1959) 

 described the relatively sudden appearance of 

 Miltilicola in sea mussel stocks of the Nether- 

 lands in 1949 and its subsequent spread to 

 many mussel beds during the following decade. 

 The organism was known to occur in Mediter- 

 ranean mussels since the beginning of the 20th 

 century (Monod and Dollfus, 1932), and in 

 1938 was found near Cuxhaven, Germany, from 

 whence it was assumed to have spread west- 

 ward to the Netherlands. Spread was thought 

 by Kuri-inga and others to be aided by mussel 

 encrusted ships, by movement of planktonic 

 larvae, and by transfer of seed mussels from 

 infested areas. MtitiUcola was also very abun- 

 dant in localized areas of the English coast in 

 1946. Korringa stated that the condition of 

 mussels was generally correlated with intensity 

 of parasitization ; mussels with less than 5 

 copepods were still healthy, those with 5 to 10 

 were visibly thinner, and more heavily infested 

 lots suffered serious mortalities. According to 

 Meyer- Waarden and Mann (1954) and Mann 

 (1956), gonad weights of infested individuals 

 were 10 to 30 percent less than those of non- 

 parasitized mussels. 



There is some indication, however, that M. 

 intestinalis exerts a less severe effect on popu- 

 lations of Mytilus (/aUoprovinciaUs than on 

 those of M. edulis, possibly because of its longer 

 association with M. (/alloprovincialis and the 

 consequent better adaptation of host and para- 

 site — as was pointed out by Fleury, Lubet, and 

 Le Dantec (1951). Hrs-Brenko (1964), for 

 e.xample, found no difference in condition inde.x 

 of parasitized and unparasitized mu.ssels (M. 

 g aUoprovinciaUs) on the Yugoslav Adriatic 

 coast, and Genove.se (1959) made similar find- 

 ings on the Italian coast. 



Infe.station of sea mussels led to poor growth, 

 thin meats (Cole and Savage, 1951; Mann, 

 1951), cream-colored rather than dark brown 



liver, failure of byssal development, and a dirty 

 red-brown color. Reproduction of the parasite 

 was accelerated by warm water, and the many 

 young parasites present in the sumnuT invaded 

 and killed mussels. Deaths occurred anu)ng mus- 

 .sels of all sizes, including ".seed." Mussels fell 

 from culture racks and died during transport 

 to markets (Briemu\ 1964). Density of mu.ssel 

 beds was believed to directly inllueiice survival 

 and multiplication of the parasite. Infestations 

 were light in area.-, where the mus.sels were 

 thinly scattered and near the surface of the 

 water. Because of the (•(nitimicd spread of 

 M]ltiUcola in the Netherlands, an extensive 

 scheme of repeated dredging of natural beds, 

 transfer of lightly infested stocks, ami destruc- 

 ti(ni of heavily infested stocks was outlined by 

 Korringa (1959) to cre.ite a barrier *'> further 

 invasion. 



Miltilicola in mussel populations grown on 

 floats in Spain was .studied by Andreu (1963). 

 He found the infestation to be greater near 

 shore where tidal currents were weak. Vertical 

 distribution of the parasite in cultured mussels 

 grown (HI 6-m. ropes was uniform in areas 

 of strong currents but increased with depth 

 where currents were weak. Such findings agree 

 well with those of Hepper (1955), who con- 

 cluded from field observations that mu.s.sels 

 raised from the bottom, or in fast-moving water 

 at either end of an estuary, were less heavily 

 infested with Miitilicitht than those on the bot- 

 tom, in slow-moving water, or in the mid- 

 regions of estuaries. Hepper felt that control 

 of the copepod was po.ssible by using ofi'-bottom 

 culture or by locating culture beds in fast- 

 moving water or at the brackish-water ends of 

 estuaries. 



M. i}ifrsfiiiiilis, except for one doubtful North 

 American record (Pear.se and Wharton, 1938), 

 is known only from Europe. It has been re- 

 ported from Germany (Gaspers, 1939; Meyer 

 and Mann, 1950, 19'")2a, 1952b; Meyer-Waarden 

 and Maim, 1956), the Netherlands (Korringa, 

 1951b, 1952b, 1953, 1957a), Belgium (Leloup, 

 1951, 1960), Scotland, England, and Ireland 

 (Ellenby, 1947: Grainger, 1951 ; Hockley, 1952; 

 Thomas, 1953; Bol.ster, 1954; Waugh, 1954), 

 the north coast of France (Dollfus, 1914, 1927; 

 Monod and Dollfus, 1932; Brienne, 19G4), the 

 northwest coast of Spain (Andreu, 1960, 1961, 



348 



U.S. FISH AND WIIDIIII. SI.RVICE 



