Age Determination and Growth Analysis Based on External Shell Rings of the Protobranch Bivalve Yoldia Notabilis Yokoyamain Otsuchi Bay, Northeastern Japan

Benthos Research, 43 : 53-66, Jul., 1992

Age Determination and Growth Analysis Based on External Shell Rings of the Protobranch Bivalve Yoldia notabilis YOKOYAMAin Otsuchi Bay, Northeastern Japan

MASAHIRO NAKAOKA

Ocean Research Institute, University of Tokyo

大槌湾に生息するブリソデガイYoldia notabilis YOKOYAMAの外部成長輪による年齢査定および成長の解析

仲岡雅裕

Abstract

NAKAOKA, MASAHIRO(Ocean Research Institute, University of Tokyo). 1992. Age Determina- tion and Growth Analysis Based on External Shell Rings of the Protobranch Bivalve Yoldia notabilis YOKOYAMAin Otsuchi Bay, Northeastern Japan. Benthos Research, 43: 53-66. Age structure and growth pattern of Yoldia notabilis in Otsuchi Bay, northeastern Japan were studied using samples collected monthly during the period between December 1989 and December 1990. Y. notabilis has growth rings on external shell surface, and it was found that the formation of the "major ring" occurs annually during late winter to early spring. Age of Y. notabilis can be determined up to seven years old by counting number of the major rings, whereas only four younger year classes are separable from size-frequency histograms. Mean shell lengths of the four youngest year classes separated by the two methods are identical to each other. The growth rate of Y. notabilis is very slow at 0 year old ; achieving only 1.3mm in shell length by the first winter. The growth becomes rapid after the first year and the animal reaches 32.0mm at the age of seven years old. The obtained growth curve shows a sigmoidal pattern and the Gompertz growth equation gives a best fit for the data.

age structure by extracting cohorts from size- Introduction frequency histograms has been undertaken widely Age determination is essential in studies of in various benthic invertebrates (see TSUTSUMI & population dynamics of long-lived species which TANAKA, 1987). However, this method often contain size overlapping year classes. Analysis of requires large number of samples to distinguish year classes. Moreover, information attained using Received August 23, 1991: Accepted March 26, this method indicates only the characters of the 1992. population at the sampling time, but not of its

53 No.43 Benthos Research Jul., 1992

history. population by external ring measurements. Fur-

For animals which possess accretionary grow- ther, the results are cross-checked by the usual ing body parts such as molluscs and echinoderms, it "size -frequency histogram" method in order to is possible in some cases to determine their age demonstrate that the ring can be accurately used as using external or internal growth rings. Age deter- an age marker. mination using these rings has an advantage over Materials and Methods those using size-frequency histograms because the age of animals can be determined individually. It is The samplings were carried out monthly also possible to examine the past growth history of between December 1989 and December 1990 at a each individual using the rings (SEED,1980). For permanent sampling station (St. Y2) which was the application of this method, however, it is neces- established at the inner part of Otsuchi Bay (39•‹ sary to determine the period of the ring formation. 19.8'N; 141•‹54.8'E). The depth of the station is 12

Growth rings are produced in various cyclical pat- to 15m, and the bottom substratum consists of terns, (e.g. daily, lunar-monthly, or annually), or muddy sand. even with aperiodical stochastic events such as Four to nine replicate samples were taken each disturbance, disease and shell damage (see LUTZ& month using a 0.1m2 Smith-McIntyre grab sampler.

RHOADS,1980; KENNISH,1980; for reviews). Sediment samples were sieved through a mesh of

The analysis of growth using growth rings has 1 mm openings and living individuals of Yoldia been carried out for various long-lived lamelli- notabilis retained on the sieve were collected. branch bivalves including Macoma balthica (e.g. Because of their slender form of the shell, animals

LAMMENS,1967; GREEN,1973; BEUKEMAet al., smaller than 1.6mm in shell length were washed

1977),Mercenaria mercenaria (e.g. KENNISH,1980; away through the sieve. In order to collect the

PETERSONet al., 1983; JONESet al., 1990), Mya specimens in smaller size-fraction, two to five sub- arenaria (e.g. BROUSSEAU,1979; GOSHIMA,1982) samples of the area of 100cm2 were taken from and Mytilus edulis (e.g. THEISEN, 1973; LUTZ, grab samples each month during the period

1976; RODHOUSEet al., 1984). However, informa- between June, 1990 and December, 1990, and ani- tion on growth of protobranch bivalve Yoldia is mals retained between sieves of 0.5mm and 1 mm still limited in spite of its wide geographical distri- mesh openings were collected under a dissecting bution (COWAN,1968)and an important role in soft microscope. bottom communities (RHOADS,1963; RHOADS& In the laboratory, shell length was measured to

YOUNG,1970; LEVINTON,1977).Only three studies the nearest 0.1mm with a caliper for animals larger have been published on the growth of Yoldia spp. than 2mm in shell length and to the nearest 0.02 hitherto ; SANDERS(1956) and LEWISet al. (1982) mm with a micrometer for those smaller than 2 for Y. limatula along the northeastern coast of mm. The number of the "major" rings on external

North America, and HUTCHINGS& HAEDRICH shell surface (see results), if countable, was then

(1984) for Y. thraciaeformis in the deep Atlantic recorded and shell length at each ring was mea-

Ocean. sured individually.

Yoldia notabilis is one of the major benthic Separation of year classes for individuals animals in Otsuchi Bay, northeastern Japan. It has retained on a 1mm-mesh sieve was carried out (1) growth rings on the external shell surface. Year by counting the number of the major rings, and (2) classes of the population of Y. notabilis in Otsuchi from size-frequency histograms by means of a Bay have been separated using size-frequency histo- nonlinear least-square method which was described grams (NAKAOKA,1989), but not by means of the and introduced into a BASIC program by AKAMINE growth rings. The present paper analyzes the age (1982). composition and growth pattern of the Y. notabilis Growth of Yoldia notabilis was analyzed by

54 Age and Growth of Yoldia notabilis

measuring shell length at growth rings. In order to where B, C, b and c are constants. The parameters construct growth curve, mean shell lengths at suc- of these equations and correlation coefficient (r) cessive growth rings were fitted into three theoreti- which represents the degree of fit between empirical growth equations; (1) the von Bertalanffy equa- cal and theoretical shell lengths were computed tion, using iterative nonlinear least-square regression analysis (SAS INSTITUTE, 1988). Lt=L•‡(1-e-k(t-to)) Results where L, is the shell length at time t, Lm the theoretical maximal shell length, k a growth con- 1. Observations of external growth ring stant, and to the theoretical time when shell length Dark, brown-colored rings are discriminated equals zero; from light, yellow-colored shell surface of Yoldia

(2) the Gompertz equation, notabilis (Fig. 1). The color pattern is produced independently of the fine grooves which appear Lt=L•‡e-Bexp(-Ct) obliquely on the shell surface at narrow and regular and (3) the logistic equation, intervals. The rings are separable into two types according to the thickness in color and the distinct- Lt=L•‡/(1+be-ct) ness from the background. The thick, distinct rings

Fig. 1 Yoldia notabilis. Photographs of shell surface showing external banding pattern. a: Shells possessing two types of rings; m=major ring, i- minor ring. Scale bar=5mm. b : Dorso-lateral view of a small shell showing the umbonal area ; p =prod issoconch, m=the smallest major ring. Scale bar =1mm. c : A large shell on which the number of the ring is uncountable near shell margin ; an arrow indicates the area where numerous rings are piled up and inseparable by eye. Scale bar-5mm.

55 Nn 43 Benthos Research Jul., 1992

(termed as "major ring") are formed at regular tainty, these larger animals were used only for the intervals, whereas the thin, faint rings ("minor measurements of the seventh and younger rings in ring") are seen irregularly between the major rings this study. (Fig. 1a). In the umbonal area, the smallest major ring is 2. Season of the ring formation recognized outside of prodissoconch (Fig. 1b). The Shell increment from the outermost major ring size of the prodissoconch is 200um in its longitudi- to shell margin was determined for animals with nal axis, and shell length at the smallest ring is less than eight major rings, and monthly mean around 1.3mm. increment was calculated for each of four size The number of the major rings is easily count- classes (0-10mm, 10-20mm, 20-30mm, and more able in the specimens with less than eight rings. In than 30mm, in shell length) separately (Fig. 2). In the specimens possessing more rings, however, it is all size classes, shell increment suddenly dropped in often difficult to count the exact number of the March, 1990, indicating the appearance of a new rings because the rings are piled up at the area near ring during February and March, 1990. The new to the shell margin (Fig. 1c). Due to this uncer- ring was discerned in 95% (35 out of 37) of the

Fig. 2 Yoldia nolabilis. Seasonal changes in shell increment (mean +SD)

from the outermost major ring to shell margin for each of four size

classes. Solid squares represent shell increments from the outer-

most ring to shell margin until February, 1990, and solid circles,

after February, 1990. Open squares indicate shell increments

from the second outermost rings after February, 1990. Numerals

represent sample sizes. Individuals in which the outermost ring

was not discerned were excluded from the measurements in March

and April, 1990 (shown by •š).

56 Age and Growth of Yoldia notabilis

individuals in March, 1990 and 96% (42 out of 44) in February (Table 1). April, 1990, and all the examined specimens had Seasonal change in shell length is examined for this ring afterwards. The ring gradually departed each year class separately (Fig. 3). Although some from shell margin after March, 1990. No abrupt fluctuations are detected, shell growth is positive in decrease in the shell increment appeared at any younger five classes. Shell length of 1989 class other measurement time, which indicates no new increased from 2.7mm in April, 1990 to 3.6mm in ring formation in other seasons. With the appear- December, 1990. Annual growth during 1990 was ance of the new ring, the outermost ring during 2.8mm, 2.7mm, 5.1mm and 2.9mm for 1988, 1987, December, 1989 and February, 1990 became the 1986 and 1985 class, respectively. However, mean second outermost ring on and after March, 1990 shell length of three oldest classes (<1983 to 1984 (Fig. 2). classes) remained at the same level throughout the From these evidences, it is suggested that the year, mainly because of large variation in shell formation of the major ring occurs annually during length within each year class. late winter to early spring. Analysis by sizefrequency histograms. Size. frequency histograms of shell length for monthly 3. Age determination samples show polymodal distributions (Fig. 4). Analysis using the rings. Eight subgroups have Three to four distinct cohorts are discerned in the been separated in the Yoldia notabilis population range smaller than 25mm in shell length (Fig. 4). according to the number of major rings (Table 1). The smallest cohort (cohort I ) appeared in April, Assuming the rings to be produced annually in 1990 at mean size of 2.3mm and it grew up to 3.5 winter, these subgroups correspond to seven year mm in December, 1990. Mean shell length of the classes (1983 to 1989 classes), and one compound second cohort (cohort II) increased from 4.5mm in class which recruited before 1983 (<1983 class). December, 1989 to 7.4mm in December, 1990, and The youngest class (1989 class) appeared on the third cohort (cohort III) from 11.9mm to 14.4 and after April, 1990 and had one major ring. The mm. The fourth cohort (cohort N) grew from 16.9 second youngest class (1988 class) had one ring until mm in February, 1990 to 22.2mm in December, February, 1990, and two rings after February due to 1990, although this cohort was not detected in some the addition of a new ring. Similarly, animals months. belonging to the seventh class (1983 class) possessed Contrary to these four cohorts, the largest six rings until February and seven rings after mode, which appears in the range more than 25mm

Table 1 Yoldia notabilis. The number of the specimens belonging to each year class which is determined by means of the growth ring analysis

57 Na 43 Benthos Research Jul., 1992

Fig. 3 Yoldia notabilis. Seasonal changes in mean shell length (•}SD) of

each year class separated by means of the growth ring.

in shell length, did not show obvious increase in its Comparisons of two methods. The monthly peak value during the year (Fig. 4). Its mean size mean shell lengths of four youngest classes fluctuated between 31.7mm (in November, 1990) obtained from above two methods are compared to and 35.3mm (in February, 1990). This mode has each other (Table 2). covered wide range of shell length (25 to 40mm), It is found that 1989, 1988, 1987 and 1986 year and therefore is considered to contain several size- classes separated using the rings correspond to the overlapping cohorts. cohorts I , II, III and N extracted from size-

58 Age and Growth of Yoldia notabilis

59 No.43 Benthos Research Jul., 1992

Table 2 Yoldia notabilis. Comparison of mean shell lengths (•}SD) of

year classes determined by means of the growth ring and the size-frequency histograms. Numerals in parentheses indicate sample sizes

60 Age and Growth of Yoldia notabilis

frequency histograms, respectively. The values of mean shell length and standard deviation of the mean, and sample size quite agree between the two methods (Table 2).

4. Age and size of the specimens in smaller size fraction In order to ascertain whether there is a younger year class in the size-fraction which passes through 1mm-mesh sieve, individuals retained between the sieves of 1mm and 0.5mm openings were collected from the subsamples, and shell length and the number of the major rings were measured for each individual. A total of 28 individuals was collected in this size-fraction. Shell lengths are distributed between 0.84mm and 1.64mm (Fig. 5). Except for one largest individual (1.64mm in shell length), all the individuals have no rings on shell surface, and are therefore considered to belong to the youngest year class which recruited in 1990. Mean shell length of this class was 0.84mm in June, 1990 (n=1), and it increased to 1.13mm (n=2) in December, 1990. The largest individual, which was collected in July, 1990, had one major ring (Fig. 5), and is considered to belong to 1989 class.

5. Growth pattern

Mean shell length at each of seven rings was Fig. 5 Yoldia notabilis. Size- calculated for all the specimens in which the rings frequency histograms for the were countable. Age-shell length relationship was samples retained between then established assuming that the ring is formed sieves of 1mm and 0.5mm annually in winter and that the recruitment occurs openings. Filled histograms in winter immediately after the spawning (NAKA- indicate individuals without

OKA,1989) at the shell length of 0.2mm, or the size major rings on the shell, and a of prodissoconch. blank one, with one major

The growth curve shows a sigmoidal pattern ring.

(Fig. 6). Growth is extremely slow during the first year (age 0+) ; mean shell length at the end of the Among three theoretical growth equations, the year is 1.3mm•}0.3 (SD). The growth becomes Gompertz curve gives the best fit for the empirical then rapid, and maximum annual growth is data (Table 3, Fig. 6). The theoretical maximum achieved at the age of three years old (6.2mm/yr). shell length (LW)obtained from this equation is 36.4

The growth gradually slows again after age 3 + mm, which is in some degree smaller than actual and mean shell length reaches 32.0mm•}2.8 (SD) shell length of the largest specimen (L=44.0 mm). at the age of seven years old.

61 Na 43 Benthos Research Jul., 1992

Table 3 Yoldia notabilis. The parameters of the von Bertalanffy, the Gompertz and the logistic growth equations determined using non-linear regression analysis (SAS INSTITUTE, 1988). r2 represents square of correlation coefficient which indicates the degree of fit between empirical and theoretical shell lengths

Fig. 6 Yoldia notabilis. Age-shell length relationship determined by

calculating mean shell lengths (•}SD) at seven smallest growth

rings. It was assumed that the ring is formed annually in winter

and that the recruitment occurs in winter at the size of 0.2mm (size

of prodissoconch). The curve represents the Gompertz curve

which is fitted for the empirical data using iterative nonlinear

least-square regression analysis (SAS INSTITUTE, 1988).

Yoldia notabilis in Otsuchi Bay occurs annually Discussion during late winter to early spring (Fig. 2). In addi- Examination of seasonal change in the shell tion, four youngest year classes separated using the increment from the outermost growth ring has rings agree well to the corresponding cohorts sepa- revealed that the formation of the major ring of rated from size-frequency histograms (Table 2).

62 Age and Growth of Yoldia notabilis

Since the cohort on the histograms has been found (TERAZAKI, 1980 ; IIZUMI et al., 1990). Foods for to be produced annually in spring (Fig. 4 ; see also the deposit-feeding animals such as benthic diatoms NAKAOKA,1989), this result again suggests that the and organic matter supplied from the water column rings are formed once in a year and are accurate to are also expected to be the lowest in winter, as use as an age marker. suggested by low organic matter flux to the bottom It is demonstrated that year classes can be during this season (NAKAOKA, unpubl.). A slow separated for up to seven year-old classes using the growth rate and formation of the growth ring in Y. growth rings. Ages are determined in 78.0% of the notabilis are probably caused by such poor nutri- examined individuals with this method. On the tional conditions in winter. other hand, only four youngest classes are discerned In the previous study, NAKAOKA(1989) consid- from the size-frequency histograms because of the ered that the smallest animals on a 1 mm-mesh overlapping of size among older classes. Ages of sieve belonged to the 0 year class, and that the only 50.1% of individuals are determined with this animals grew to 5 mm in shell length before the analysis (Fig. 4). These results indicate that the first winter. However, the analyses of the smaller growth ring analysis is more effective in the age size-fraction as well as the measurements of the determination of the Yoldia notabilis population. growth rings in this study have revealed that the Nevertheless, age determination of animals older ages had been underestimated one year younger in than seven years old are found to be difficult even the last study. In reality, the growth of Yoldia with the external ring analysis, because in these old notabilis is very slow during the first year, reaching animals, it is often unable to distinguish the rings only 1.3mm by the first winter, and it takes more from each other near shell margin (Fig, 1c). Intro- than a year to appear on a 1mm-mesh sieve. The duction of other methods such as analysis of growth extremely slow growth of early juveniles has been ring in the inner shell layer, long-term culture and also reported in the brackish-water bivalve, Cor- mark-recapture experiment will be necessary to bicula japonica (MANGYO et al., 1983), and may be determine the older year classes and maximum life found in other bivalves if animals on finer sieving span of Y. notabilis. mesh are examined precisely (but see MOLLER & Similar growth rings have been found in other ROSENBERG, 1983; BACHELET, 1986; DAUVIN & nuculanid protobranch bivalves including Yoldia LENTIL, 1989). spp. (SANDERS, 1956; ANSELL & PARULEKAR, The growth pattern of Yoldia notabilis is 1978; HUTCHINGS & HAEDRICH, 1984; GILKINSON compared to those of other Yoldia species published et al., 1986). Among them, SANDERS(1956) showed up to date (Fig. 7). Although maximum shell that the growth ring of Y. limatula in Long Island lengths are similar (around 40 to 50mm), growth Sound was laid down during winter. The formation rates vary in a large degree among three species. of annual rings in winter has been reported in many Especially, growth rates during the early stage are other molluscs of high latitudinal region, and it has remarkably higher in Y.limatula and Y. been considered to be caused by slow shell growth thraciaeformis than in Y. notabilis. SANDERS(1956) at low water temperature and reduced food supply reported that shell length of Y. limatula in Long (KENNISH, 1980; WILLIAMSON& KENDALL, 1981). Island Sound reaches 9 to 10mm by the first winter, In the case of Y. notabilis, growth is slow during and LEWIS et al. (1982), 14 to 18mm for the popula- winter and then becomes rapid after early spring tion in the Bideford River, eastern coast of Canada. (Fig. 3 ; see also NAKAOKA,1989), and new growth HUTCHINGS & HAEDRICH (1984) estimated the rings are discernible from shell margin with this annual growth rate of Y. thraciaeformis in deep change of growth rate (Fig. 2). In Otsuchi Bay, it Atlantic Ocean (1000 to 1500m deep) to be 7.5mm/ has been reported that chlorophyll a content and yr during first four years. However, the growth zooplankton biomass become minimum in winter analyses in these studies were based on samples of

63 No.43 Benthos Research Jul., 1992

Fig. 7 Yoldia spp. Comparison of growth curves of three Yoldia populations. The Gompertz curve is used for Y. notabilis, and the von Bertalanffy curves for Y. limatula and Y. thraciaeformis, because each curve gives the best fit for each population among three theoretical growth curves (the von Bertalanffy, the logistic and the Gompertz curves). The data for Y. limatula are derived from LEWIS et al. (1982) and for Y. thraciaeformis from HUTCHINGS& HAEDRICH (1984). restricted sizes or seasons, and the smallest year Marine Research Center, Ocean Research Institute, class might be overlooked in these populations. University of Tokyo for the use of field and labora- Contrary to the marked differences in early stage, tory facilities, and to T. KAWAMURA, K. MORITA, I. the growth rate of Y. notabilis in the later stage is TAKEUCHI, A. TSUDA and H. SUGISAKI for their similar to that of Y. thraciaeformis. (Fig. 7). assistance in field work. The author also thanks to In conclusion, the analysis of external growth S. GOSHIMA for providing very helpful suggestions ring was proved to be a very effective method in and advices, and to H. MUKAI, S. OHTA and Y. obtaining many valuable data on the age and SHIRAYAMA for critically reading the manuscript. growth of Yoldia notabilis. Application of this References method in future studies will yield important information on population dynamics and life history of AKAMINE, T., 1982. A BASIC program to analyze this species. the polymodal frequency distribution into nor- mal distributions. Bull. Japan Sea Reg. Fish. Acknowledgments Res. Lab., 33: 163-166 (in Japanese with Eng- The author is grateful to the staffs of Otsuchi lish abstract).

64 Age and Growth of Yoldia notabilis

ANSELL, A. D. and A. H. PARULEKAR,1978. On the IIZUMI, H., K. FURUYA, I. TAKEUCHI, K. KUTSU rate of growth of Nuculana minuta (MULLER) WADA, A. TADA and K. KAWAGUCHI, 1990. (Bivalvia ; Nuculanidae). J. Moll. Stud., 44: 71 Dynamics of nutrients and chlorophyll a at -82 . Otsuchi Bay: Analysis of the data of monthly BACHELET, G., 1986. Recruitment and year to year observation. Otsuchi Mar. Res. Cent. Rep., 16: variability in a population of Macoma balthica 63-65 (in Japanese). (L.). Hydrobiologia, 142: 233-248. JONES, D.S., I.R. QUITMYER,W.S. ARNOLD and D. BEUKEMA, J.J., G.C . CADEE and J.J.M. JANSEN, C. MARELLI, 1990. Annual shell banding, age, 1977. Variability of growth rate of Macoma and growth rate of hard clam Mercenaria spp. balthica (L.) in the Wadden Sea in relation to from Florida. J. Shellfish Res., 9 : 215-225. availability of food. In, Biology of benthic KENNISH, M.J., 1980. Shell microgrowth analysis : organisms, 11th Europ. Symp. Mar. Biol., Mercenaria mercenaria as a type example for Galway, ed. by B.F. KEEGAN., P.O'CEIDIGH & research in population dynamics. In, Skeletal P.J.S. BOADEN, Pergamon Press, Oxford, pp. growth of aquatic organisms, ed. by D.C. 69-77. RHOADS & R. A. LUTZ, Plenum Press, New BROUSSEAU, D.J., 1979. Analysis of growth rate in York, pp. 255-292. Mya arenaria using the von Bertalanffy equa- LAMMENS,J.J., 1967. Growth and reproduction of tion. Mar. Biol., 51: 221-227. a tidal flat population of Macoma balthica (L.). COWAN, I. MCT., 1968. The interrelationships of Neth. J. Sea Res., 3 : 315-382. certain boreal and arctic species of Yoldia LEVINTON, J.S., 1977. Ecology of shallow water MOLLER, 1842. Veliger, 11: 51-58. deposit-feeding communities Quisset Harbor, DAUVIN, J.-C. and F. GENTIL, 1989. Long-term Massachusetts. In, Ecology of marine benthos, changes in populations of subtidal bivalves ed. by B.C. COULL, University of South Car- (Abra albs and A. prismatica) from the Bay of olina Press, Columbia, South Carolina, pp. 191- Morlaix (Western English Channel). Mar. 227. Biol., 103: 63-73. LEWIS, J.B., S. SALEH, H.M. REISWIG and C.M. GILKINSON, K.D., J.A. HUTCHINGS, P.E. OSHEL LALL, 1982. Growth, production and biomass and R.L. HAEDRICH, 1986. Shell microstruc- of the burrowing protobranch mollusc Yoldia ture and observations on internal banding pat- limatula in the Bideford River, Prince Edward terns in the bivalves Yoldia thraciaeformis Island, Canada. Mar. Biol., 70: 173-179. STORER, 1838, and Nuculana pernula MULLER, LUTZ, R.A., 1976. Annual growth patterns in the 1779 (Nuculanidae), from a deep-sea environ- inner shell layer of Mytilus edulis L.J. Mar. ment. Veliger, 29: 70-77. Biol. Ass. U.K., 56: 723-731. GOSHIMA, S., 1982. Population dynamics of the soft LUTZ, R.A. and D.C. RHOADS, 1980. Growth pat- clam Mya arenaria L., with special reference to terns within the molluscan shell : An overview. its life history pattern. Publ. Amakusa Mar. In, Skeletal growth of aquatic organisms, ed. by Biol. Lab., 6 : 119-165. D. C. RHOADS & R.A. LUTZ, Plenum Press, GREEN, R. H., 1973. Growth and mortality in an New York, pp. 203-254. arctic intertidal population of Macoma balthica MANGYO, H., F. MIDORIKAWAand K. ARITA, 1983. (Pelecypoda, Tellinidae). J. Fish. Res. Board Growth rate of juveniles of the brackish-water Can., 30: 1345-1348. bivalve, Corbicula japonica in Jusanko, Aomori HUTCHINGS, J.A, and R.L. HAEDRICH, 1984. Prefecture. Abstracts of 30th Ecological Meet- Growth and population structure in two species ing, Okayama, p. 242 (in Japanese). of bivalves (Nuculanidae) from the deep sea. MOLLER, P. and R. ROSEN BERG,1983. Recruitment, Mar. Ecol. Prog. Ser., 17: 135-142. abundance and production of Mya arenaria and

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Cardium edule in marine shallow waters, west- Japanese). ern Sweden. Ophelia, 22: 33-55. THEISEN, B.F., 1973. The growth of Mytilus edulis NAKAOKA,M., 1989. The growth and reproductive L. (Bivalvia) from Disko and Thule district, cycle of Yoldia sp. [aff. Y. notabilis Greenland. Ophelia, 12: 59-77. YOKOYAMA](Mollusca ; Bivalvia) in Otsuchi TSUTSUMI, H. and M. TANAKA, 1987. A new Bay. Otsuchi Mar. Res. Cent. Rep., 15: 21-27 method for measurement of body size and (in Japanese). analysis of generation structure of polychaete PETERSON, C.H., P.B. DUNCAN, H. C. SUMMERSON populations, using a microcomputer. Benthos and G. W. SAFRIT, Jr., 1983. A mark-recapture Res., 31: 18-28 (in Japanese with English test of annual periodicity of internal growth abstract). band deposition in shells of hard clams, Mer- WILLIAMSON, P. and M. A. KENDALL,1981. Popula- cenaria mercenaria from a population along the tion age structure and growth of the trochid southeastern United States. Fish. Bull., 81: Monodonta lineata determined from shell rings. 765-778. J. Mar. Biol. Ass. U. K., 61: 1011-1026. RHOADS, D.C., 1963. Rates of sediment reworking by Yoldia limatula in Buzzards Bay, Massa- 和文摘要 chusetts, and Long Island Sound. J. Sed. Pet- rol., 33: 723-727. 大槌湾に生息するブリソデガイYoldaa notabilis RHOADS, D.C. and D.K. YOUNG, 1970. The influ- YOKOYAMAについて,1989年12月から1990年12月ま ence of deposit-feeding organisms on sediment での期間に毎月採集した試料をもとに,年齢査定およ stability and community structure. J. Mar. び成長様式の解析を行った.ブリソデガイの殻表には Res., 28: 150-178. 2種類の成長輪が観察される.そのうち"major ring" RODHOUSE,P.G., C.M. RODEN,G.M. BURNELL, M. は年に1回,冬から春にかけて形成されることが明ら P. HENSEY, T. MCMAHON, B. OTTWAY and T. かになった.年齢査定は,(1)成長輪解析,(2)殻長 H. RYAN, 1984. Food resource, gametogenesis 頻度分布を用いたコホート解析,の2方法を用いて行 and growth of Mytilus edulis on the shore and った.その結果,成長輪解析からは7才年級群まで査 in suspended culture : Killary Harbour, 定できるのに対し,殻長頻度分布からは4才年級群ま Ireland. J. Mar. Biol. Ass. U. K., 64: 513-529. でしか分離できず,前者の有効性が示唆された.また, SANDERS, H.L., 1956. Oceanography of Long 2方法により分離された対応する年級群の平均殻長は Island Sound 1952-1954. X. The biology of 同じであった.成長輪の形成間隔より成長様式を調べ marine bottom communities. Bull. Bingham たところ,ブリソデガイの成長は0才年級群では非常 Oceanogr. Coll., 15: 345-414. に遅く,1年目の冬までに殻長1.3mm程度にしか達 SAS INSTITUTE, 1988. SAS/STAT user's guide, しないことが判明した.1才以降成長速度は増加し, release 6.03 edition. SAS INSTITUTE, Cary, 7才で平均殻長32.0mmに達する.この結果得られた North Carolina, 1028 pp. 成長曲線はシグモイド型を示し,Gompertzの成長方 SEED, R., 1980. Shell growth and form in the 程式に最もよく一致する. Bivalvia. In, Skeletal growth of aquatic organisms, ed. by D.C. RHOADS & R.A. LUTZ, MASAHIRO NAKAOKA Plenum Press, New York, pp. 23-67. Ocean Research Institute, University of Tokyo, TERAZAKI, M., 1980. Zooplankton in Otsuchi Bay. 1-15-1 Minamidai, Nakano, Tokyo 164, Otsuchi Mar. Res. Cent. Rep., 6: 1-5 (in Japan