File:American malacological bulletin (1988) (17968729310).jpg

Title: American malacological bulletin
Identifier: americanmal6719881990amer (find matches)
Year: 1983 (1980s)
Authors: American Malacological Union
Subjects: Mollusks; Mollusks
Publisher: (Hattiesburg, Miss. ?) : (American Malacological Union)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
182 AMER. MALAC. BULL. 6(2) (1988) These species had relatively distinct external growth bands and were aged by the growth ring method. Later, the same valves were thin-sectioned, as previously described. Ages determined by these two methods were plotted graphically, and a Wilcoxon signed rank test was used to compare differences. RESULTS ANNULUS VALIDATION A total of 521 (36%) of the 1452 marked mussels was recovered from the three streams (Table 2). Recovery rates of specimens from Big Moccasin Creek and the North Fork Holston River were similar, 49.1 and 47.1% respectively; the largest species, Pleurobema oviforme, was the most frequently recovered. Both sites on the New River yielded low returns (3.2%) because of specific problems. Muskrats (Ondatra zibethicus L. along the New River removed 55 marked spec- imens (found in shell middens) in June-July 1982, and one enclosure of 50 mussels was vandalized in October. In addition, a thick mat of Elodea developed by fall 1982 and summer 1983, and caused considerable siltation and mortality of marked mussels. Of the three marking methods tested, notching of
Text Appearing After Image:
Fig. 1. Thin-section of the umbonal region of Pleurobema oviforme showing internal growth lines (bar = 1 mm). Table 2. Recovery and validation of annulus formation on mussels marked in Big Moccasin Creek (BMC), North Fork Holston River (NFHR), and New River (NR), western Virginia. Oil Cal 11/ OfJCUIco Mussels Recovered Kin No /0 valid 3 ted Big Moccasin Creek Pleurobema oviforme 83 58 7 IVItzUIUlIIUUo CUiliaUlLUb 101 38 V "ivOQ VQI f L/AC7f 1" 90 60 Q Subtotal 274 49 26 North Fork Holston River P. oviforme 109 60 4 M. conradicus 63 38 9 V. vanuxemi 62 42 20 Subtotal 234 47 33 New River Lasmigona subviridis 13 3 4 Total 521 63 valves was the most useful for recording shell growth and an- nulus deposition. Annuli appeared as dark bands in sectioned valves (Clark, 1974; Lutz and Rhoads, 1980), and were evi- dent on 25 (27%) of the 94 notched specimens recovered at site II in the streams. Notching readily identified the origin of incremental growth and subsequent growth at the shell margin (Fig. 1). Thin-sections through the notch clearly delineated incremental growth and the presence of a growth band. An annulus was validated on all notched shells that grew more than 1 mm/yr and on several shells that grew 0.5 to 1.0 mm/yr. Several specimens, marked between 1979 and 1982 and collected in 1983, showed one annulus for each year at large. Although the disc tags remained firmly attached to all specimens upon recovery, mussels with only tags were less useful for documenting growth bands. Only 38 (9%) of 425 recovered specimens from site I in the streams were useful for annulus validation. All mussels that grew more than 1.5 mm/yr were validated, but lack of precision with caliper measurements and a fragile shell margin prevented annulus validation on a higher percentage of the slower-growing specimens. Fingernail polish on shell margins was completely ineffective. Within 3 months after marking, it had sloughed from the shells apparently due to abrasion in the substratum. Annulus formation was documented on 63 (12%) of the 521 specimens recovered from all sites (Table 2). Although this percentage appears low, only specimens with readily measurable incremental growth in length (1.0-1.5 mm, de- pending on marking method and species) could be used for validation. Occurrence of single (annual) growth bands was confirmed in the shells of all four marked species. Because 83% of the recovered specimens grew less than 1 mm, growth bands formed during the last year on these mussels were nearly indistinguishable from those formed during the penultimate year (Table 3). Growth was most rapid in Lasmigona subviridis, the most thin-shelled species, whereas

Note About Images