Table Of Contentch, vol.1, no.4, pp.260-266, 6Figs., 30 December, 1997
i£) by trie Paiaeuiu^.ogical Society of Japan
Shell microgrowth patterns of bivalves reflecting
seasonal change of phytoplankton abundance
SHIN'ICHI SATO
Natural History Institute, National Science Museum, 3-23-1 Hyakunin-cho, Shinjuku-ku, Tokyo 169, Japan.
Received 28 March 1997 Received manuscript accepted 20 November 1997
;
Abstract Seasonal patterns of shell microincrement growth in a venerid bivalve Phacosomajaponicum
wereanalyzedforthethreepopulationsfrom Hakodate,Ariake,and Kagoshima BaysaroundtheJapanese
coasts. ThenorthernmostHakodatepopulation in Hokkaidogrewrapidlyina limited intervalbetweenlate
spring and summer. The numberofmicroincrementswithin anannual incrementinthespecimensfrom
this population was smallest (200-250increments) among the three samples of populations examined,
andeach microincrementwidthwaslargest(0.25-0.3mm)atthecentralpartofanannualincrement By
contrast, in the southernmost Kagoshima population in southern Kyushu, shell growth occurred slowly in
a long term between early spring and fall. The specimens forming this population are characterized by
havingthenarrowestmicroincrements(each0.10-0.12mm)and largestnumberofmicroincrementsinthe
annual increment(300-350increments). In thisspecies, it has been confirmed thatthe growing season
reflectsthe seasonal changes of phytoplankton abundance. The phytoplankton bloom usually occurs in
spring inembaymentsofnorthernJapanandinsummerinthoseofcentralandsouthernJapan. InAriake
Bay (central Kyushu), however, the phytoplankton becomes most abundant in winter and remains at low
levels in the other seasons. The Ariake population of P.japonicum showed the most active growth in
intervals between winterand earlyspring. Inthissample,the microincrementwidth attained a maximum
in the earlier portion of each annual increment and the annual increment showed a particularly right-
skewed pattern which reflects the winter phytoplankton bloom in this bay.
Key words: Bivalve, Phacosomajaponicum, Phytoplankton bloom, Shell microgrowth analysis
Introduction In this study, to delineate the relationship between shell
microincrementgrowth patterns and the seasonal change of
Shell microgrowth analysis is a useful method for ecologi- phytoplankton abundance, seasonal patterns of shell mi-
cal research of extant and fossil molluscs, because micro- croincrement growth in P. japonicum were analyzed forthree
growth increments preserve information aboutenvironmental populations around the Japanese coasts.
and physiologic conditions (Rhoads and Pannella, 1970
;
Kennish, 1980; Lutz and Roads, 1980; Jones, 1983). In the Material and methods
venerid bivalve Phacosomajaponicum treated inthis paper, it
has been confirmed that winter and spawning breaks are Seasonal changes of shell microincrement growth were
formed annually in the shell microgrowth pattern, and that examined for the samples from the subtidal sand flat of
they can be used to estimatethe age ofsexual maturityand Kamiiso Coast, Hakodate Bay, southern Hokkaido (41 49'N,
shell growth rate in extantand fossil samples(Tanabe,1988; 140°42'E) and the intertidal sand flats of Nagahama Coast.
Tanabe and Oba, 1988; Sato, 1994,1995,1996). Ariake Bay, central Kyushu (3241'30"N, 1303330 E) and of
Growth and reproduction of bivalves are generally influ- Shigetomi Coast, Kagoshima Bay, southern Kyushu (31 42
enced by a number of environmental factors such as water 30"N, 13038'E) (Figure1). Living individuals were collected
temperature, salinity, and food availability. Sato (1998) sug- monthly from Ariake and Kagoshima Bays during January-
gested that monthly shell growth pattern and reproductive September, 1995, and those from Hakodate Bay were sam-
cycles of P.japonicum are strongly influenced by seasonal pled on several occasions from September, 1991 to March.
change of food availability, represented by phytoplankton 1996 (Figure1). Seasonal change of shell microgrowth
abundance. Shell microgrowth analysis is useful to recon- patterns were analyzed for three-year old specimens from
struct the seasonal change of shell growth, so that it will be each locality.
possible to estimate the seasonal change of phytoplankton Shell microgrowth patterns were also examined for the
abundance based on shell microgrowth analysis of fossil samples from the other ten localities around the Japanese
specimens. coasts(Figure1). Oftheten samples, thetwo samplesfrom
—
Shell microgrowth patterns of bivalves 261
Wakkanai Port and Yatsushiro Bay consist only of dead
specimens, whereas thosefrom the other eight localities are
represented by living animals. Also, in Wakkanai Port and
Ishikari and Hakodate Bays, animals from the subtidal zone
Dateofsampling
(50):Numberolliving were recovered from commercial port landings, and at the
other localities, those from the intertidal zone were sampled
manually at low tide.
AriakeBay To examine the shell microgrowth patterns, a single valve
MFaetb..1187,.11999955((2104)) MatsushimaBay from each specimen was sectioned from the umbo to the
JAMpuarny.e111445...111999999555(((222292))) Jury10,1991(23) ventral margin along the axis of maximum growth. The
SAJueulpgy..1077,..111999999555(((112250))) sectioned valve was polished and etched with 5% acetic
acid for 10minutes, and then an acetate peel was prepared
for each specimen by pressing a sheet of acetyl cellulose
Mar16,1995(7) film named as "Bioden R. F. A." (34^m in thickness, Oken
Shoji Co., Ltd.) on the etched surface flooded with acetone.
Growth increments in each acetate peel were viewed by
May6,1994(151 means of a Nikon V-16 profile projector at magnification,
X100. The maximum width of each microincrement was
measured successively from the umbo to the ventral margin
Figure1. Locations and dates of collection for samples using a digital micrometer (accuracy±1 /*m) attached to the
of Phacosoma japonicum treated in this paper. Number in profile projector.
parentheses shows the sample size. Seasonal changesofshell growthand gonaddevelopment
in the Hakodate, Ariake and Kagoshima samples were also
(—a)DM—ontHhalkyodsahetlelBgaryo(w1t9h91p-a1t9t9e6r)ns (c—)TDe—mpeHraaktoudrateeBay(1989)
--0-- AriakeBay(1995) --0-- AriakeBay(1995)^
o-- KagoshimaBay(1995) 30-, —•© KagoshimaBay(1995)
120
3-100 ü 25- ;"iX
20- P
Tc) 80 .-•<?
.o*c 60 S0QE}. 15- ..-"" x>' / \°
ecn 40 <5 10-
Ol 5c3
>Cl>
20 5-
———— —
t 1 1 1 1 1 1 1 1 1 n- i i i i i i i i i i i i
50 (b) Gonaddevelopmentalpatterns (d) Foodavailability
100 R 300 e
45 E
OE) Iïï -200 o «
o 40 sc 2^ 50 ca to
100 -oEt.o
« 35 '...*
o
1o= .<g — <E
JFMAMJJASO
30 1 1 1 1 1 1 1 1 1 1 J F M Mi J 1 J1A 1 S1O T N 1 D
Figure2. Seasonal changes of shell growth (a) and gonad development (b) in mature (>4years old) speci-
mens of P.japonicum from Hakodate, Ariake and Kagoshima Bays [mean value and the range of one standard
deviation (vertical bar)are indicated], comparedwithannualvariationsofwatertemperature (c) andfoodavailabil-
ity (d) near the sampling localities. Sources of environmental data: (1) unpublished data of the Hokkaido
Hakodate Fisheries Experimental Station in 1997, (2) unpublished data of the Kumamoto Prefectural Fisheries
Research Station in 1997, (3) unpublished data of the Kagoshima Environmental Research and Service in 1997.
262 Shin'ichi Sato
examined following the method described by Sato (1995, Hakodate, Ariake and Kagoshima Bays and the seasonal
1998). Gonad index [(gonad weightx100)/total soft body changes of some environmental factors near the sampling
weight] and growth index [net growth (distance from last localities. This species exhibits distinct geographic varia-
winter break to shell margin)/expected annual growth (dis- tion in seasonal patterns of shell growth and reproductive
tance from lastwinter break to expected nextwinter break)] cycles (Figure2a, b). Shell growth and gonad development
were calculated in monthly collected samples. The extent were activefrom FebruarytoApril inthepopulationofAriake
of the expected annual growth for each individual was Bay. For example, mean gonad index of the sample from
estimated using the Ford-Walford equation (Ford, 1933; Ariake Bayhad already increased atahigh value(morethan
Walford, 1946). The equation is expressed as 40%) as early as April, although the gonad index reaches a
HR+i=aHR+b amnadxigmounmadindJeuvneelo(pFmigeunrte2obc)c.urrOendtdhuericnogntrJaurnye, sahneldl gJurloywtihn
where HR istheshell heightatthe R thwinterbreak(inmm), the Hakodate Bay population andfrom April toAugust in the
Hr+i isthe shell heightatthe R+l th winterbreak(in mm), Kagoshima Bay population. In these samples, mean gonad
and a and b are constants determined by a simple regres- index kept to low values (less than 40%) during January to
sion between HR and HR+i of different individuals of the April and then increased rapidly in Mayand June (Figure2b).
same sample. Using this equation, shell height at the Because Ariake Bay and Kagoshima Bay are adjacent to
expected nextwinter break ofeach individual (HR+i)can be each other, seasonal changes of water temperature and
estimated from shell height atthe lastwinter break (HR)and salinity are similar between them (Figure2c; Sato, 1998).
constants at each age class {a, b). Data of growth index However, they are markedly different in the seasonal abun-
and gonad indexofthesamplesfromAriakeand Kagoshima dance of phytoplankton. In Kagoshima Bay, the amount of
Bays were quoted from Sato (1998). phytoplankton increasesfromJunetoAugust(Figure2d). In
Ariake Bay, however, phytoplankton abundance attains a
Results maximum from January to March. The phytoplankton
bloom generally occurs in spring in embayments of northern
Seasonal changes of growth and reproductive cycle in P. Japan and in summer inthoseofcentral and southernJapan
japonicum and some environmental factors (lizumi et al., 1990; Yamashita, 1982), so that the winter
Figure2 showsseasonal shell growth and gonad develop- bloom in Ariake Bay is a very unique phenomenon in the
mental patterns inthesamplesofPhacosomajaponicumfrom Japanese coasts. Based on these data, Sato (1998) con-
Hakodate Bay (Sep. 91 - Mar. 96)
DO 200 300 400 00 200 300 400 00 200 300 400 500
Incrementnumber 1 Incrementnumber Incrementnumber
100Incr2e0m0entn3u00mber400 500 100Incr2e0m0entn3u00mber400 I00Incr2e0m0entn3u00mber400 500
Figure3. Shell microgrowth patterns from the 2nd winter break to shell margin in the six specimens of P.
japonicum, each ofwhich was collectedfrom Hakodate Bay in March, 1996, June, 1992,July,1994andSeptember,
1991 respectively. W2, W3: the 2nd and 3rd winter breaks which are fitted by eye, respectively.
* —
Shell microgrowth patterns of bivalves 263
eluded that growth and reproductive cycles of P. japonicum examined, the number of microincrements within the 3rd
are primarily influenced by food availability not by water annual increment issmallest(200-250 increments), and each
temperature. microincrement width is largest (0.25-0.3mm) at the central
part of an annual increment.
Comparison of shell microgrowth patterns
Shell microgrowth patterns in the specimens from the The sample from Ariake Bay
three localities were examined and compared with each In the specimens recovered from Ariake Bay, microincre-
other. The specimens from each locality showed a similar ments near the end of an annual increment are narrow and
growth pattern of microincrements. Shell microgrowth pat- crowded, so that the winter break is usually obscure (Figure
terns in the selected three-year-old specimens from Ha- 4). Because rapid shell growth occurs between winter and
kodate, Ariake and Kagoshima Bays are shown in Figures3 earlyspring inthis bay(Figure2a),winterbreaksappeartobe
to 5. formed in late fall or early winter. Comparison of the shell
microgrowth patterns among monthly collected specimens
The sample from Hakodate Bay also reveals that after passing the 3rd winter break, microin-
In the specimens from Hakodate Bay, a growth cessation crementwidth rapidly increases in February, andthen gradu-
mark represented bythe discontinuityofthe microincrement ally decreasesfrom April to September (Figure4). Because
sequence is observed at the boundary between two annual microincrement width attains a maximum in February, the
increments (W2 and W3 in Figure3). This cessation mark microincrement sequence within each annual increment
was caused byshell dissolution during the winterseason (= shows a right-skewed pattern. In this sample, each mi-
winter break) (Tanabe, 1988), and in the specimens from this croincrementwidth is narrow(0.15-0.25mm), andthe number
bay the winter break is clearer than in the other two bays. of microincrements is considerably large in the 3rd annual
All of the specimens collected in March secreted fewer increment (250-300 increments) compared with the Ha-
microincrements after the formation of the 3rd winter break kodate sample.
than those collected in June and July. Each microincre-
ment width rapidly increases in going from June to July and The sample from Kagoshima Bay
thereafter decreases in September. Thus it is suggested In the specimens from Kagoshima Bay, the microincre-
thatthespecimens in Hakodate Bay rapidlygrow in a limited ment width increased slowly after passing the 3rd winter
interval between late spring and summer, and in the other break, and microincremental growth continued during a long
seasons they do not grow. Among the three samples interval between March and September (Figure5). There-
Ariake Bay (Feb. - Sep. 95)
c0.05
100 200 300 400 100 200 300 400 100 200 300 400 500
Incrementnumber Incrementnumber Incrementnumber
June'95 •=-0.25 July'95
| i |
E
W2 VJ3
'g0.15-
P 1
Incrementobi—ni—vl HJLmini
o-1
100 200 300 400 5001 o IOC> 200 300 400 5Û 100 200 300 400 500
Incrementnumber Incrementnumber Incrementnumber
Figure4. Shell microgrowth patterns from the 2nd winter break to shell margin in the six specimens of P.
japonicum, each ofwhich was collected from Ariake Bay in February, April, May, June, July and September, 1995
respectively. W2, W3: the 2nd and 3rd winter breaks which are fitted by eye, respectively.
:&4 Shin'ichi Sato
fore, the maximum microincrement width is smallest (0.10- Winter breaks are very clear because the ventral margin of
0.12mm), and the number of microincrements in the 3rd each annual increment is partly dissolved in winter.
annual increment is largest(300-350increments)among the Besides the Hakodatesample, the northern type includesall
three samples examined. In this sample, the maximum the samples from northern Japan; i.e. Wakkanai Port, Ishi-
microincrement width appeared during May and June, so kari Bay (both in Hokkaido) and Mutsu Bay (northernmost
that each annual increment exhibited a symmetrical pattern. Honshu). Ages of sexual maturity in those samples are at
Also, a clear interruption of microincrement growth least four years, with maximum shell height of more than 6
appears in the central part ofthe 3rd annual increment(SB. cm (Table1).
in Figure5). This interruption proved to be the result of a IntheAriaketypetypicallyrepresented bythesamplefrom
spawning event (=spawning break) (Sato, 1995). Based on Ariake Bay, the accretionary pattern of microincrements in
this break, the onset of sexual maturity in this sample can the 3rd annual increment is broad and right-skewed (Figure
therefore be determined as two years old. 6). Wide microincrements occurred during the limited inter-
val between winterand earlyspring. Interestingly,this inter-
Three types of shell microgrowth patterns and their geo- val corresponds to the season of phytoplankton bloom
graphical range around the Japanese coasts occurrence (see Figure2d). Specimens from Isahaya and
Comparison of the accretionary pattern of microincre- Yatsushiro Bays also belong to this type. Age of sexual
ments among the thirteen local samples of Phacosoma maturity of the Ariake-type specimens is four years, and
japonicum revealed the presence of three types; i.e. north- maximum shell heightofall samples inthistype ismorethan
ern, southern and Ariake types (Figure6). These three 6cm (Table1).
types can be distinguished on the basis ofthe difference in The southern type is found in the specimens from Kago-
the shape ofthe shell microgrowth pattern in the 3rd annual shima Bay. The microincrement sequence in the 3rd
increment. annual increment is characterized by a symmetrical and low
The northern type is represented by the sample from hillshape (Figure6). Animals in Kagoshima Bay showed a
Hakodate Bay. The accretionary pattern of microincre- remarkable growth in summer the season of growth coin-
;
ments in the 3rd annual increment has avery sharp peak at cideswiththatofphytoplanktonabundance. Therefore,the
the central portion, because every microincrement widens water temperature in growing season is much higher (20-
rapidly in a limited interval between late spring and summer. 30°C) than those of the other types (10-20°C). This kind of
Kagoshima Bay (Feb. - Sep. 95)
100 200 300 400 500 600 100 200 300 400 500 600
Incrementnumber Incrementnumber Incrementnumber
Figure5. Shell microgrowth patterns from the 2nd winter break to shell margin in the six specimens of P.
japonicum, eachofwhichwascollectedfrom KagoshimaBay in February,April, May,June,AugustandSeptember,
1995 respectively. W2, W3, S.B.: the 2nd and 3rd winter breaks and spawning break which are fitted by eye,
respectively.
Shell microgrowth patterns of bivalves 265
Types Northerntype Southerntype Ariaketype
ploocpaullitaiteisoonfsthe WBaayk,kaHnaakiodPaotrte,BIasyhi,kari MMaitksauwsahBiamya,BSaeyt,oTIonklyanodBSaeya,, YAraitaskueshBiaryo,BIasyahayaBay,
MutsuBay TsuyazakiInlet,KagoshimaBay
Maximum
shellheight 6.5-8.0cm 4.6-5.8cm 6.3-6.8cm
AmagteuroiftySexual 4-5yrs 2-3yrs 4yrs
Growingseason
ofthisspecies May-Aug. Apr.-Sep. Feb.-Apr.
Temperaturein
growingseason 10-20°C 20-30°C 10-20°C
Spheyatsoopnlaonfkton Mar.-May June-Aug. Jan.-Feb.
bloomoccurs
I"
3mpSiarnihtdccatrrapeeornemgnnerouniofantwlstthhheell £iIsE.00..-012 ^1A01J|0k 20tIi0 300 SfÎE.00..023 ^10^0À^..^200^ 30IiIII"0 çfIsE.00..-0123 100 200 II 300
Incrementnumber Incrementnumber Incrementnumber *
Figure6. Three shell microgrowth types recognized in the populations ofP.japonicum around the Japanese
coasts compared with the life history characteristics and environmental conditions of each type.
microincrementgrowth waswidelyrecognized inthe popula- type populations is at most three years, and maximum shell
tionsaroundthecentraltosouthernJapanesecoastsinclud- height of all samples in this type is less than 6cm (Table1).
ing Matsushima Bay (northeastern Honshu), Tokyo and Therefore, thesouthern-type populationscan also be clearly
Mikawa Bays (both in central Honshu), Seto Inland Sea distinguished from the populations of the othertwo types by
(Shikoku), Tsuyazaki Inlet and Kagoshima Bay (both in the differences in life-history traits such as age of sexual
Kyushu). The geographical boundary between the popula- maturity and maximum shell height.
tions showing northern-type and southern-type microincre-
ment growth occurs between Mutsu Bay and Matsushima
Bay (ca. 39°-40°N). Age of sexual maturity in the southern-
Table1. Summaries of life historyand shell microgrowth patternsofP.japonicum ateach locality. Maximum
asymptotic shell height were calculated by Gompertz equation (see Sato, 1994).
Maximum Ageof Numberofmicro- Microincrement Shapeofthe
Locality Latitude asymptotic sexual incrementswithin widthofthelargest 3rdannual Type
shellheight maturity the3rdannual increments(mm) increment
(cm) (yrs) increment
WakkanaiPort 45°25'N 8.02 >5 150-200 0.25-0.30 Symmetrical
IshikariBay 43°10'N 7.21 5 200-250 0.25-0.30 Symmetrical Northern
HakodateBay 41°49'N 6.49 4 200-250 0.25-0.30 Symmetrical type
MutsuBay 40°52'N 6.63 ? 200-250 0.25-0.30 Symmetrical
MatsushimaBay 38°22'N 5.15 3 250-300 0.10-0.15 Symmetrical
TokyoBay 35°19'N 5.80 3 200-300 0.15-0.20 Symmetrical Southern
MikawaBay 34°46'N 5.21 3 250-300 0.10-0.15 Symmetrical type
SetoInlandSea 33°58'N 4.95 3 250-350 0.10-0.15 Symmetrical
TsuyazakiInlet 33°47'N 5.37 3 250-300 0.15-0.20 Symmetrical
IsahayaBay 32°52'N 6.34 4 250-300 0.15-0.25 Rightskewed Ariake
AriakeBay 32°41'N 6.53 4 250-300 0.15-0.25 Rightskewed type
YatsushiroBay 32°37'N 6.86 ? 250-300 0.15-0.25 Rightskewed
KagoshimaBay 31°42'N 4.61 2 300-350 0.10-0.12 Symmetrical southerntype
266 Shin'ichi Sato
monthlyobservation. OtsuchiMarine Research Center
Discussion
Report, no.16, p.63-65. (in Japanese)
This study revealed that the populations of Phacosoma Jones, D.S., 1983: Sclerochronology: reading the record of
japonicum aroundtheJapanesecoastscanbeclassified into the molluscan shell. American Scientist, vol.72, p.
384-391.
the northern, southern and Ariake types based on the shell
microgrowth pattern (Figure6). The boundary between the Kennicsehn,ariaM.Jm.e,rc1en9a8r0i:aSahsella tmyipceroegxraomwptlheafnoarlyrseisse.arcMheri-n
northern- and southern-type populations of this species population dynamics. In, Rhoads, D.C. and Lutz, RA.
corresponds to the northern limit of the Zoogeographie eds., SkeletalGrowthofAquaticOrganisms,p.255-294.
ranges of typical Japanese temperate-water species such Plenum Press, New York.
as Meretrix lusoria, Mactra veneriformis and Trapezium lira- Lutz, R.A. and Rhoads, D.C, 1980: Growth patterns within
turn (Matsushima, 1984). Around the Japanese coasts fac- the molluscan shell. In, Rhoads, D.C. and Lutz, R.A.
ing the Pacific Ocean, these species do not live north ofthe eds., SkeletalGrowthofAquaticOrganisms,p.203-254.
Sanriku Coast (ca. 39°-40°N), where the water temperatures Plenum Press, New York.
annuallyrangefrom 8°Cto23°C(Tamura,1966 Matsushima Matsushima, Y., 1984: Shallow marine molluscan assem-
;
and Ohshima, 1974). P.japonicum is distributed in Mutsu blages ofpostglacial period intheJapanese islands-Its
Bay (ca. 40°N), but the shell microgrowth and life-history historical and geographical changes induced by the
patterns in the northern-type populations markedly differ environmental changes. Bulletin of Kanagawa Prefec-
from those in the southern-type populations. These results tural Museum, no.15, p.37-109. {in Japanese with
suggestthatthe geographic boundarybetween39°Nand40° English abstract)
N (annual range of water temperature from 8°C to 23°C) is a Matsushima, Y. and Ohshima, K., 1974: Littoral molluscan
critical point reflected by the physiological conditions for faunaofthe Holoceneclimaticoptimum(5,000-6,000y.
gmeaoTnghyreapbhiAivracilaavlkeleyspnteeyicpgiehebsionrlciilvniugndgebdoayntshtiehnecsteaindmtaprlallfelsaKtysu.fsrhoum.theIsathharyeae Rhoa1dsBh.3seP5,.l-)l1D5.i9gCn.r.Jo{aawinptnadhJna.PppaanatnnQteeeulrsalntease,rwGnii.nat,hry1eE9cnR7oge0llsoie:gsaTyhrhcaeahb,nsutdrsvaoelcp.toa)f1l3e,mooenlcolo.ul3so,cgaypn..
Bay is a small cove in Ariake Bay, sothatseasonal change Lethaia, vol.3, p.143-161.
ofphytoplanktonabundance inthisbayappearstobesimilar Sato, S., 1994: Analysis ofthe relationship between growth
to that in the main part of Ariake Bay. In Yatsushiro Bay, and sexual maturation in Phacosoma japonicum
phytoplankton bloom also occurred in winter (Tsuruta et al., (Bivalvia: Veneridae). MarineBiology,vol.118, no.4,p.
1986). In summary, the growing season of P.japonicum is 663-672.
strongly influenced by the annual pattern of food (phyto- Sato, S., 1995: Spawning periodicity and shell microgrowth
plankton) abundance, and shell microgrowth patterns pre- patterns of the venerid bivalve Phacosoma japonicum
serve well seasonal changes of phytoplankton abundance. (Reeve, 1850). The Veliger, vol.38, no.1, p.61-72.
Therefore, shell microgrowth analysis of fossil bivalves is Sato, S., 1996: Life history of a venerid bivalve Phacosoma
expected to be useful in reconstructing seasonal change of japonicum and its evolutionary implications. 85p., Ph.
phytoplankton abundance in paleoembayments. D. thesis, University of Tokyo.
Sato, S.,1998: Geneticandenvironmental control ofgrowth
and reproduction of Phacosoma japonicum (Bivalvia
:
Acknowledgments Veneridae). The Veliger, (in press)
Tamura, T., 1966: Seedlings of Shallow Marine Animals.
The author thanks K.Tanabe (Univ. Tokyo) for his critical 331 p. Koseisha Book Company, Tokyo, (in Japanese)
reviews of the manuscript and valuable comments, M.Sato Tanabe, K., 1988: Ageand growth ratedeterminationsofan
(Kagoshima Univ.), T.Oji, K. Endo, and other colleagues at intertidal bivalve, Phacosoma japonicum, using internal
the Paleobiological Laboratoryof Univ. Tokyofortheirfruitful shell increments. Lethaia, vol.21, p.231 241.
advice, and S.Goshima (Hokkaido Univ.), T. Noda (Hokkaido Tanabe, K. and Oba, T., 1988: Latitudinal variation in shell
Univ.),T. Miyauchi,T. Katsutaand H.Yamashitafortheirhelp growth patterns of Phacosoma japonicum (Bivalvia;
in collecting samples. This study was partly supported by Veneridae) from the Japanese coast. Marine Ecology
Grants-in-Aid for Scientific Research from the Japan Soci- Progress Series, vol.47, p.75 82.
ety for the Promotion of Science (Research Fellow of Doc- Tsuruta, A., Ueno, S., Ohgai, M. and Yamada, M., 1986:
toral Class, No.4407) and Fujiwara Natural History Founda- Study on the seasonal and horizontal distributions of
phytoplankton communities in Yatsushiro Sea, using a
tion.
cluster analysis. Bulletin of the Japanese Society of
Scientific Fisheries, vol.52, no.11, p.1947-1955. (in
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