NOTES 



ANNUAL BAND DEPOSITION WITHIN 



SHELLS OF THE HARD CLAM, 



MERCENARIA MERCENARIA: CONSISTENCY 



ACROSS HABITAT NEAR 



CAPE LOOKOUT, NORTH CAROLINA 



The presence of periodically repeating features in 

 the preservable hard parts of various organisms 

 allows scientists in several disciplines to make im- 

 portant inferences about the rates and timing of past 

 events (Jones 1980; Rhoads and Lutz 1980). Analysis 

 of growth lines deposited in shells of bivalve molluscs, 

 for example, finds powerful application in the fields 

 of paleontology (Rosenberg and Runcorn 1975), an- 

 thropology (Clark 1979), population ecology (Ken- 

 nish 1980), and fisheries biology (Peterson et al. 

 1983). Possession of a reliable age marker in a bivalve 

 shell enables fisheries biologists 1) to construct age- 

 frequency distributions for various populations, 

 which reflect the age-specific mortality rates and 

 help permit estimates of sustainable yield, 2) to 

 calculate individual growth rates and their variability 

 among habitats, and 3) to understand age-specific 

 reproductive schedules in exploited populations. 



Unfortunately, the potential rewards in applying 

 this aging technique have encouraged widespread 

 use of growth line analysis prior to performing the 

 necessary controls to test the annual periodicity of 

 line deposition (Clark 1974; Gould 1979; Jones 1981). 

 Because of the tremendous potential utility of this 

 aging technique, we carried out mark-recapture tests 

 of the annual nature of growth band deposition in 

 shells of the commercially important hard clam, 

 Mercenaria mercenaria, in a North Carolina sound 

 (Peterson et al. 1983). Although these experiments 

 provided convincing evidence that M. mercenaria 

 deposits a reliable annual marker in the form of an 

 internal summer growth band in its shell, this study 

 was carried out in only a single locality in Back 

 Sound, NC. Patterns of growth band deposition in 

 bivalve molluscs may vary with environment on 

 several scales: 1) over a broad geographic scale, M. 

 mercenaria deposits summer bands in Back Sound, 

 NC, and in Chesapeake Bay, but winter bands in all 

 localities in northeastern states (Pannella and 

 MacClintock 1968; Rhoads and Pannella 1970; Ken- 

 nish and Olsson 1975; Clark 1979; Clark and Lutz 

 1982; Fritz and Haven 1983; Peterson et al. 1983); 

 2) among habitats within estuaries, Protothaca 

 staminea appears to deposit unambiguous annual 



bands in muddy sand but not in a clean-sand habitat 

 in Mugu Lagoon, CA (Peterson and Ambrose 1985); 

 and 3) among nearby individuals within a single 

 habitat, both Chione fluctifraga and Protothaca 

 staminea from within the same restricted sample at 

 Mugu Lagoon exhibit radically different patterns of 

 daily line deposition (Hughes and Clausen 1980). 

 We present here results of additional tests of the an- 

 nual nature of internal growth band deposition in 

 shells of M. mercenaria placed for 2 yr in several 

 different field localities and estuarine habitats, in 

 order to test whether our earlier (Peterson et al. 

 1983) demonstration of annual banding in North 

 Carolina's M. mercenaria is robust to change in local 

 habitat. 



Materials and Methods 



lb extend the generality and power of our previous 

 results, we designed a mark-recapture experiment 

 to examine the frequency and clarity of band deposi- 

 tion in M. mercenaria at 5 additional sites (Fig. 1) 

 within Carteret County, NC, near Cape Lookout. 

 These sites were chosen to represent a wide geo- 

 graphic spread among several local water bodies, to 

 permit contrasts between vegetated and unvegetated 

 habitats, and to include more sandy (coarse) sub- 

 strate than that in our original site One site was 

 selected on a fine sand flat in the North River about 

 12 km from our earlier Middle Marsh study site in 

 Back Sound. Two sites were chosen about 38 km 

 from Middle Marsh near the western end of Bogue 

 Sound by the town of Cape Carteret: one on a fine 

 sand flat and the other in a seagrass bed with mix- 

 ed stands of Zostera marina and Halodule wrightii. 

 The other two sites were situated in Core Sound 

 about 6 km from Cedar Island Point and about 47 

 km from our initial Middle Marsh study site: one on 

 a sand flat and the other in a Halodule wrightii 

 meadow. All sites were on shallow subtidal bottom, 

 accessible by wading and amenable to recovery of 

 marked animals. 



Tkble 1 summarizes the results of particle-size 

 analyses done on duphcate surface (0-5 cm) sediment 

 cores taken in August-September 1981 at each site 

 to permit comparisons among the five new and one 

 previous study sites. The five new sites are clearly 

 characterized by having much coarser sediments 

 than the previous study site but differ among them- 

 selves in sediment grade (Tkble 1). Contemporaneous 



FISHERY BULLETIN: VOL. 83, NO. 4, 1985. 



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