DOCUMENTATION OF ANNUAL GROWTH LINES IN OCEAN QUAHOGS, ARCTICA ISLANDICA LINNE JOHN W. ROPES.' DOUGLAS S. JONES,' STEVEN A. MURAWSKI.' FREDRIC M. SERCHUK,I AND AMBROSE JEARLD, JR.I ABSTRACT About 42.000ocean quahogs,Arctica islandica Linne. were marked and released ata 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 preparationofacetate peels and examination byoptical microscopy ormicro­ 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 periodicityofmicrost.ructure ia documented. providing a basis for accurate age analysesofthis commercially important species. Numerous bivalve species form periodic growth lines of clearly separating such shell features was in their shells (Rhoads and Lutz 1980). Internal needed. growth lines found in the shells of ocean quahogs, Recent investigators of age phenomena in ocean Arctica islandica Linne, have stimulated interest in quahogs have microscopically examined the shells using these markings to determine age and growth and acetate peel images produced from sectioned. (Thompson et a1. 1980a, b), since fishery exploitation polished. and etched shells. This method greatly has increased significantly within the past decade aided separating the many crowded growth layers in 3 (Serchuk and Murawski 1980 ). the hinge plate and neal' the ventral valve margin of Documentation ofage and growth ofocean quahogs large. old specimens. Lutz and Rhoads (1977) found has been incomplete. Some studies included no alternating bands of aragonitic prisms and complex­ account of aging methodologies (Thorson in Turner crossed lamellar microstructures in the inner shell 1949; Jaeckel 1952; Loosanoff 1953; Skuladottir layer of ocean quahog shells that they believed were 1967); in others, concentric "rings" or "bands" related to periods of aerobic and anaerobic respira­ fOlmed in the periostracum ofsmall quahogs «ca. 60 tion. Thompson et a1. (1980a. b) reported that inter­ mm in shell length) were considered annuli, but nal growth bands corresponded toexternal checks on validation ofthe annual periodicity ofthesemarkings the valves and that the internal growth bands were was not provided (Loven 1929; Chandler 1965; formed by successive deposition of two repeating 4 Caddy et a1. 1974; Chene 1970 ; Meagher and Med­ growth layers or increments. Jones (1980) labelled 5 cof 1972 ). Microstructure of ocean quahog shells the growth increments (GI) as GI I and GI II, since has been studied. but the analyses did not each was microstructurally distinct. had thickness, specifical1y distinguish growth lines from growth and was formed within a time frame of several months. increments (Sorby 1879; B0ggild 1930: Taylor et a1. Forthese reasons. he considered the GI I layer to be 1969,1973; Lutz and Rhoads 1977, 1980). A means unlike minute "growth lines" or "striations" appear­ ing as subdaily deposits in the shells ofotherbivalves 'Northeast Fisheries Center Woods Hole Laboratory, National (Gordan and Carriker 1978); the GI II layer became Marine Fisheries Service, NOAA. Woods Hole, MA 02543. "Department of Geology. University of Florida, Gainesville, FL thinner and ill-defined from the GI I layer with 32611. ontogeny. 3Serchuk. F.M. and S.A. Murawski. 1980. Evaluation and status of ocean quahog. A rctWJ. is/andiro (Linnaeus) populations off the Since growth bands in ocean quahog shells seem to Middle Atlantic Coast of the United States. U.S. Dep. Commer.. lack microstructures of possible subannual peri­ NOAA, NMFS, Woods Hole Lab. Doc. 80-32, 4 p. odicities. the definitions of a growth line and growth <CMnj!, P.L. 1970. Growth. PSP accumulation, and other features of ocean quahog(AretWJ. is/a·ndiro). Fish Res. Board Can., increment formulated by Clark (1974a, b) have St. Andrews BioI. Stn., Orig. Manuscr. Rep. 1104. 34 p. general application. Clark (1974b: 1) defined the for­ "Meagher, J.J., and J.e. Medrof. 1972. Shell rings and growth rate of ocean cll1ms (A retic« isla:ndic«). Fish Res. Board Can.• St. meras "abruptorrepetitive changes in the character Andrews BioL Stn., Orig. Manuscr. Rep. 1105, 26 p. of an accreting tissue" and the latter as "the thick- Manuscript acceptedJuly 1983. FISHERY BULLETIN: VOL. 82. NO. I. 1984. FISHERY BULLETIN: VOL. 82. NO.1 ness or volume of tissue formed by accretionary METHODS growth between successive growth lines." In fact, Jones (1980:333) identified the layers as a "consist­ A commercial clam dredge vessel, the MY J)im!l' ently thin, dark gray, translucent increment" of pris­ Maria, was chartered for the marking operation dur­ matic microstructures which was "easily distin­ ing 25 July to 5 August 1978. The knife of the hy­ guished from" homogeneous and crossed micro­ draulic dredge was 2.54 m wide, and the cage was structural layers. lined with 12.7 mm square-mesh hardware cloth to Assessment research on ages of ocean quahogs retain small clams. Ocean quahogs for marking were requires accurate counts and measurements of collected within 9 km ofthe plantingsiteand released growth increments. Age observations are cus­ during a 10-d period (ca. 17,000 on 26 July, 3,000 on tomarily made of acetate peel images under optical 2 August. and 21.000 on 4 August 1978). Two 0.7 microscopes with transmitted light. An important mm thick carborundum discs. spaced 2 mm apart assessment requirement is that an annual increment and mounted in the mandrel of an electric grinder, has a distinct beginning and end. The concept of a produced distinctive parallel, shallow grooves from growth line forming between successive growth the ventral margin up onto the valve surface (Ropes increments fulfills that requirement. andMerrill 1970). Fouroperators ofgrinders marked Counts of supposed annual growth bands seen in about 1,600 clams/h. Groups (ca. 3.000-8.000) of the shells of ocean quahogs by Thompson et a1. marked clams were released at loran-C coordinates (1980a, b) resulted in slow growth rates and an within a rectangular area of about 3 by 6 JlS. extreme longevity estimate of 150 yr. Slow growth Marked clam recoveries were made in conjunction rate and suspiciously long life for a bivalve seemed to with annual clam resource surveys. During recovery invalidate the thesis of only a single growth line and operations. a Northstar 6000fi loran-C unit and Epsco growth incrementbeingformed annually. Supportive loran-C plotteraided ina systematic search ofthe plant­ evidence included finding similar bands in surf ing site. Marked clam recoveries were highly variable. dams; finding a low number of bands formed during On 20 and 21 August 1979 and about 387 d afterthe the onset of sexual maturity that were not explained marking operation. 43 hydraulic dredge tows at the by less thananannual frequency; finding anexpected planting site captured 14.043 ocean quahogs and 74 number of bands in small specimens of known age; (0.5%) were marked; on 9 September 1980 and 773 d finding an expected number of bands formed after the marking operation. 1,899 ocean quahogs sequentially in samples taken frequently during 2 yr were captured in 2 dredge tows and 249 (13.1 %) were that had only an annual periodicity; finding a line marked. Some marked specimens were damaged, deposited during the fall-winter, a period coinciding but 67 recovered in 1979 and 200 recovered in 1980 with spawning; and finding ages determined by were alive and had intact paired valves. radiometric analyses that were comparable with Recaptured specimens were frozen to prevent band counting. The latterthreetypesofinvestigation periostracum loss from drying and to facilitate open­ have beenexpandedbyJones (1980) andTurekianet ing without shell damage. Microscopic examination a1. (1982) with the same results. As part ofthe study. of 267 notched shells was made to assess the effects I. Thompson (pel's. comm.) marked and released of marking and to obtain growth measurements. ocean quahogs in the natural environment. but none Shell measurements were made to the nearest 0.1 was recovered. Direct and readily comprehended mm by calipers: growth after marking was measured observations of shell growth after marking were con­ to the nearest 0.01 mm by an ocular micrometer in a sidered to be important additional evidence in sup­ dissecting microscope. Acetate peels of all marked port of the thesis of an annual periodicity of growth ocean quahogs were prepared hy the procedures de­ line and growth increment deposition. scrihed hy Ropes(19R2'). Briefly.radial sectionsfrom In 1978. the National Marine Fisheries Service the umbo to ventral margin were produced on left marked large numbers of ocean quahogs for release valves. orientedtoinclude the broadestsurfaceofthe and recovery at a site 53 m deep and 48 km south­ single prominenttoothin the hinge. This exposedthe southeastofShinnecockInlet. LongIsland. N.Y., (lat. internal growth lines in the valve and hinge tooth for 40"21'N.long.72 24'W). Detailsofthis project have later treatment. The paired notch marks in a valve been reported in Murawski et a1. (1982). Periodicity of growth line formation and shell accretion after 'Reference to trade names does not imply endorsement by the notching of recovered ocean quahogs and the micro­ National Marine Fisheries Service. NOAA. 'Rope•. ,I. W. 19R2. Procedure. for pl'eparinl( acetate ppels of structure of unmarked and marked shells are de­ embedded valves ofArctil'a islandica for aging. 1I.S. Dep. Commer.• scribed herein with photographic documentation. NOAA. NMFS. Woods Hole Lab.• Doc. 82-18. 8 p. 2 ROPES ET AL.: GROWTH LINES OF OCEAN QUAHOGS were not usually oriented in the above plane of radial was no evidence ofrepairby shell covering the cracks sections, so additional radial cuts were made to in quahogs recovered 2 yr after marking. expose growth lines in the notch area. Subsequently. shells were embedded in an epoxy resin, and the cut Sectioned Shells shell edge ground on wetable carborundum paper and polished.