DOCUMENTATION OF ANNUAL GROWTH LINES IN 

 OCEAN QUAHOGS, ARCTICA ISLANDICA LINNE 



John W. Ropes, 1 Douglas S. Jones, 2 Steven A. Murawski, 1 

 Fredric M. Serchuk, 1 and Ambrose Jearld, Jr. 1 



ABSTRACT 



About 42,000 ocean quahogs, .Arcif'ca islandica Linne, were marked and released at a deep (53 m) oceanic site 

 off Long Island, New York, in 1978. Shells of live specimens recovered 1 and 2 years later were radially sec- 

 tioned, polished, and etched for preparation of acetate peels and examination by optical microscopy or micro- 

 projection; selected specimens were similarly prepared for examination by scanning electron microscopy. 

 Specific growth line and growth increment microstructures are described and photographed. An annual 

 periodicity of microstructure is documented, providing a basis for accurate age analyses of this commercially 

 important species. 



Numerous bivalve species form periodic growth lines 

 in their shells (Rhoads and Lutz 1980). Internal 

 growth lines found in the shells of ocean quahogs, 

 Arctica islandica Linne, have stimulated interest in 

 using these markings to determine age and growth 

 (Thompson et al. 1980a, b), since fishery exploitation 

 has increased significantly within the past decade 

 (Serchuk and Murawski 1980 1 ). 



Documentation of age and growth of ocean quahogs 

 has been incomplete. Some studies included no 

 account of aging methodologies (Thorson in Turner 

 1949; Jaeckel 1952; Loosanoff 1953; Skuladottir 

 1967); in others, concentric "rings" or "bands" 

 formed in the periostracum of small quahogs (<ca. 60 

 mm in shell length) were considered annuli, but 

 validation of the annual periodicity of these markings 

 was not provided (Loven 1929; Chandler 1965; 

 Caddy et al. 1974; Chene 1970 4 ; Meagher and Med- 

 cof 1972 5 ). Microstructure of ocean quahog shells 

 has been studied, but the analyses did not 

 specifically distinguish growth lines from growth 

 increments (Sorby 1879; Btfggild 1930; Taylor et al. 

 1969, 1973; Lutz and Rhoads 1977, 1980). A means 



■Northeast Fisheries Center Woods Hole Laboratory, National 

 Marine Fisheries Service, NOAA, Woods Hole, MA 02543. 



department of Geology, University of Florida, Gainesville, FL 

 32611. 



3 Serchuk, F.M. and S.A. Murawski. 1980. Evaluation and status 

 of ocean quahog, Arctica islandica (Linnaeus) populations off the 

 Middle Atlantic Coast of the United States. U.S. Dep. Commer., 

 NOAA, NMFS, Woods Hole Lab. Doc. 80-32, 4 p. 



*Ch6ne\ P.L. 1970. Growth, PSP accumulation, and other 

 features of ocean quahog (Arctica islandica). Fish Res. Board Can., 

 St. Andrews Biol. Stn., Orig. Manuscr. Rep. 1104, 34 p. 



5 Meagher, J.J., and J.C. Medcof. 1972. Shell rings and growth 

 rate of ocean clams (Arctica islandica). Fish Res. Board Can., St. 

 Andrews Biol. Stn., Orig. Manuscr. Rep. 1105, 26 p. 



Manuscript accepted July 1983. 



FISHERY BULLETIN: VOL. 82, NO. 1, 1984. 



of clearly separating such shell features was 

 needed. 



Recent investigators of age phenomena in ocean 

 quahogs have microscopically examined the shells 

 and acetate peel images produced from sectioned, 

 polished, and etched shells. This method greatly 

 aided separating the many crowded growth layers in 

 the hinge plate and near the ventral valve margin of 

 large, old specimens. Lutz and Rhoads (1977) found 

 alternating bands of aragonitic prisms and complex- 

 crossed lamellar microstructures in the inner shell 

 layer of ocean quahog shells that they believed were 

 related to periods of aerobic and anaerobic respira- 

 tion. Thompson et al. (1980a, b) reported that inter- 

 nal growth bands corresponded to external checks on 

 the valves and that the internal growth bands were 

 formed by successive deposition of two repeating 

 growth layers or increments. Jones (1980) labelled 

 the growth increments (GI) as GI I and GI II, since 

 each was microstructurally distinct, had thickness, 

 and was formed within a time frame of several months. 

 For these reasons, he considered the GI I layer to be 

 unlike minute "growth lines" or "striations" appear- 

 ing as subdaily deposits in the shells of other bivalves 

 (Gordan and Carriker 1978); the GI II layer became 

 thinner and ill-defined from the GI I layer with 

 ontogeny. 



Since growth bands in ocean quahog shells seem to 

 lack microstructures of possible subannual peri- 

 odicities, the definitions of a growth line and growth 

 increment formulated by Clark (1974a, b) have 

 general application. Clark (1974b:l) defined the for- 

 mer as "abrupt or repetitive changes in the character 

 of an accreting tissue" and the latter as "the thick- 



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