ecological and taxonomic aspects of anadara (mollusca...
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ECOLOGICAL AND TAXONOMIC ASPECTS OF ANADARA (MOLLUSCA : BlVALVIA)
IN FIJI AND SOME NEIGHBOURING [SLAND GROUPS
A thesis presented to the University of the South Pacific
.(can A, Msiybin
as purlin! fulfillment of the require in CM Us
For the degree of Master of Science
August (989
DECLARATION:
I declare that this thesis has not been submitted for any previous
application for a higher degree at any other university and that it contains
no material published or written by any other person without (hie reference in
the text.
A, May bin
1.1 Background to tlie project study
Although bivalves of the genus Anadara. arc an important traditional
source of dietary protein for indigenous Fijians living in the coastal areas
of the larger Fiji Islands, these shellfish have received very little
scientific attention (Uwatc, et, g_L, 1984). Indeed, even shell collectors
have tended to ignore them because their shells arc not particular!}'
attractive, being a very ordinary shape and rather drab in colour.
In rural areas, villagers living near th'e coastal mudflats glean for
Anadara by raking through the surface layer of sandy-mud with their
fingers or toes, or alternatively with a knife. It is not unusual for
women to spend the hours of low tide searching the mudflats for these
and other edible molluscs. Some harvesting is carried out on a more
intensive scale for sale by the basketful in urban markets. For example,
about fifty baskets of Anadara - each containing one hundred or so are
sold at the Suva market each week for one dollar a basket. In this case,
the Anadara come from Namara in Tailevu, which is about thirty
kilometers from Suva (Fig. 3). Similarly, women in the greater Suva area
glean the mudflats from Cave Island to Laucala Island, for a selection of
molluscs with which to feed their families.
Occasionally, scientific reports of the Fiji Government Ministry of
Primary Industries, connected with fisheries research and development
have mentioned Anadara as a possible species for nquncuJturc,
(Navakalomara, 1982). However, this has never been followed up and
Anadara have not been cultivated in Fiji as they have in Japan and South
6
East Asia (Rabnnal ct. a t , 1981). There lias however, been considerable
research and cultivation of the better known bivalves, oysters
fCrassostrea spp.) and green mussels (Perna vi rid is) in several areas of
Fiji. It is possible that if Anadara were cultivated in Fiji the product
would be too highly priced for the local market and its value as an
export item would be doubtful, as westerners generally arc not familiar
with the species.
Probably the first scientific account relating to Anadara in Fiji was
that published by H.J. Squires cj. ah, in the Fiji Journal of Agriculture in
1973, Squires, who was working for the Fiji Government at the lime,
carried out a survey to estimate tJic annual removal rate of cockles
(Anadara spp.) and surf clams fLatona spp.) from Wailoalon Beach, Ntuli.
Their objective was to obtain data from which an estimate of annual
income that villagers living in the area might reasonably expect. Thus,
using transects and quadrats, the population density of Andaia in the
Wailoalon area was estimated.
A. J, Butler's report (1983) to the Institute of Marine Resources,
USP, appears to be the only other published account of biological data
concerning the Fiji Anadara species. This report incorporates daia
collected by USI' (IMR) students, relating to catch numbers and size-
frequencies (B. Chand, 1980 - unpublished student manuscript report)
together with data on inorphometrics, population density, gonnd states,
weight of the soft parts, cpibiota and parasites, based on work carried
out by the author and M. G. King (IMR) during 1,981 and early 1982.
7
Prior to the above study> Butler (1983) carried out a l i terature
search and came to the conclusion that "Little appears to have been
published on the ecology of the Arcidae generally, and nothing has been
recorded about the ecology of kaikoso in Fiji."
A similar situation exists in the other South Pacific island states of
Vanuntu, Samoa and Tonga. Very little information is available
concerning the ecology, taxonomy, distribution or general biology of
native Anadara species. Mention in most publications is limited to species
lists, poster diagrams and inshore fisheries market surveys (Lewis, 1986;
Zann et. aj,, 1984a, 1984b; Spenncmann, 1987).
On the other hand, there appears to be a fairly extensive literature
on species of Anadara that arc cultivated in the northern hemisphere, i.e.
A. granosn in Malaysia, A. subcrenata in Japan and A., broughioni in
Japan and Korea, Much of this work has been reviewed by Broom (1985),
however, the only South Pacific species that Broom mentions in this
publication is A. cornea and he refers to Butler (unpublished data).
Therefore, the objectives of the following investigations were
threcfold:-
1. To establish how many species of Anadara inhabit the coasial
margins of Fiji and determine which species they are.
2. To investigate two ecological aspects of the most common
species found in Fiji, size-frequency distribution and
relative abundance on the Suva Point-Muanivatu mudflats,
and seasonal condition of the gonads.
3. To compare the taxonomic status of the species of Anadara found in
Fiji with tliat of the species found in Vanuatu, Samoa and Tonga,
Data for the project were collected over a four year period on a
part-time basis (1985 - 1988), with funding provided by the University of
the South Pacific Research Committee (0701-0065).
1.2 Classification (Emerson and Jacobson, 1976)
PHYLUM ; Mollusca
CLASS : Bivalvia
SUPER-FAMILY : Arcacea
FAMILY : Arcidae
SUB-FAMILY ; Anadarinne
GENUS : Anadara
1.3 Morphological characteristics of the genus
Members of the genus Anadara are epibenthic bivalves that show
some primitive morphological features - notably, an external chevron
type ligament, a straight taxodont hinge, unfused mantle margins and
byssus in some (although there is no byssal gape). An unusual feature
of the genus is the possession of haemoglobin in the blood (Barnes,
1980, Alexander, 1979).
9
Generally, the shells are trapczoid in shape. Some have the
posterior margin greatly extended, while others are more square, The
heavy shells have radial ribs originating from the beak and extending to
all margins, except (he hinge. The beak curves noticeably towards the
anterior. Ribs sometimes have median grooves and may be nodulose.
Periostracum growth is conspicuous, being black or dark brown in colour.
The shell margins arc fluted and the interior of the shell is a non-
lustrous white (Fig. 1).
1.4 World distribution patterns
Compared wiih other genera of Arcidac, Anaclara is geologically
fairly young (Lini, 1968). The fossil record shows that the first few
species appeared in the Oligocene, but by the Miocene there were many,
widely distributed species of Anadara,
Today there are about sixty living species (Lim, 1968). Mostly
these sue found between 20°N and 30°S, that is, in the tropics and sub-
tropics, where they inhabit the intcr-tidal mudflats and sub-tidal areas,
seaward of mangrove forests, Species of Anndara found in the Pacific
include:- A. antiouata (L,), A. broiightoni (Schrcnck), A_. crebricostata
(Reeve), A. grand is (Brodcrip and Sowcrby), A. aranosa (L.), A
incouivalvis (Brugicrc), A. maculosn (Reeve), A. nuilticostata (Sowcrby), A .
nodifcra (von Martens), A. subcrcnata (Lisclikc), A. trapezia (Deshnyes),
A. troschcli (Dunkcr), A, tubcrculosa (Sowcrby) and A, ventricosa
(Lamarck) (Fig, 2).
11
2. SPECIES OF THE GENUS ANADARA IN FIJI
2.1 Introduction
The islands of Fiji lie between 177 degrees West and 175 degrees
East, and between 15 and 22 degrees South, in the path of the westward
flowing South Equatorial ocean current. Because the larger islands have
mountain ranges that lie at right angles to the S.E. Trade winds, each
has a marked "wet" zone on the windward side and a "dry" zone to
leeward.
In the "wet" zone, high rainfall averaging about 312 cm/year
(Kennedy, 1966) gives rise to numerous rivers, some of which are
comparatively large, e.g. Nadi, Rewa and Dreketi . During the rainy
season (November to March) these rivers carry down heavy loads of silt.
Deposition of the silt in and around the river mouths supports extensive
mangrove forest and sheltered, intertidal mudflat ecological systems. In
these areas the humidity is constantly high and the air temperature
usually over 20°C.
Although temperatures are slightly higher in the "dry" zones,
rainfall is lower and there is a fairly marked dry season. Humidity is
also generally lower. Mangrove and intertidal mudflat development is
much less extensive.
From November to March, the equatorial front brings warm north-
westerly winds to the group, causing unsettled weather and occasional
cyclones.
12
Generally, species of Anadara are called "kaikoso" by the indigenous
Fijians, although in some areas this name is reserved for specimens found
below the low-tide mark. Where this is the case, Anadara found in the
intertidal area arc called "kaivulavula". Wherever these bivalves arc
found, they are enten with enjoyment, as an important source of dietary
protein supplementing fish and meat.
2.2 Identification of Anadara species
The most commonly found species of Anadara in Fiji has been called
A. antiouata (Lin.) by most workers, including Glude (1972), Cernohorsky
(1971) and Morton and Raj (1983). However, ButJer (1983) adopted the
name A. cornea (Reeve) on the recommendation of S. Boyd at National
Museum of Victoria (Butler, personal communication) and this has been
used subsequently by Lewis (j986). Abbott, of the Delaware Museum of
Natural History, suggested that the most common species was probably A^
uropygmelana (Bory St. Vincent, 1824) (personal communication to Secto,
IMR, USP, 1984).
A second, less common, species A. subcrennta (Lischkc), was
mentioned by Squires el aj.. (1973) as possibly being present. More
recently Parkinson (1982) states in his list of bivalve species recorded
from Fiji, A. scaphn maculosa. A. tricenicosta. A. inequavalvis and A.
fibula. However, Parkinson docs not give the source of his information.
13
Thus, in an attempt to determine which species of Anadara are
present in the Fiji Islands, specimens were collected from many parts oT
the group and subjected to two major areas of investigntion;-
J. Shell morphomctrics - a standard procedure used by many
authors in species description, e.g. Wolff e l aj.. (1987)
and Ting ej. a],. (1972).
2. Subsequent comparison with available standard
descriptions.
It was hoped that at least some shell measurements would establish
diagnostic criteria for each species which, visually, do not vary greatly.
The shell measurement most commonly used in species descriptions is the
number of ribs per shell. In the genus Anadara there is some variation
of rib number per shell within each species. Measurement of length and
height, and subsequent conversion to a length:hcight ratio, gives a more
informative description of shell shape than words, As with rib number,
shape varies within a species and although Anadara arc basically
trapezoid, some have the posterior margin more exaggerated than others.
In the search for structural characteristics that could be diagnostic to
the species, the number of teeth and their arrangement was considered to
be a possibility and thus the teeth were counted and their arrangement
noted on all specimens. Similarly the sculpture of the cardinal area was
included in the investigation, as this characteristic may be considered as
diagnostic (Lim, 1968).
14
2.3 Methods
Anadnra shells were collected from 35 sepa ra t e locations within the
Fiji group (Fig. 3). Each shell was given an ident i ty number and
analysed for length, height, rib number* rib s cu lp tu re , hingc-l inc length,
number of teeth, beak position and card ina l area sculp ture ,
2.3.1 Ribs (number nnd sculpture)
The number of ribs on each shell was counted and recorded.
Observations relating to the presence or absence of median grooves,
additional fine str iat ions and nodules, was also recorded (Fig. 4).
21
Sculpture in the form of a median g roove r u n n i n g l eng thwise
down the centre of the ribs was seen only on the shells wi th 30 or
more ribs. The actual number of r ibs wi th m e d i a n grooves var ied
considerably. Some shells had none a t al l , but the r e m a i n d e r had
grooves on a few or many of the an te r io r r ibs . T h e a v e r a g e n u m b e r
of anterior ribs with median grooves, for the whole sample , was M.
A few shells had very fine s t r i a t ions r u n n i n g pa ra l l e l to ihc median
groove on each side of it. An even sma l l e r n u m b e r had t iny
nodules on the ribs near the beak.
2,4.2 Shell measurements
Within the sample the smallest shells m e a s u r e d wcrc:-
No. 16 length = 1.4cm, Height = 1.0cm, L / H r a t i o = 1.40
No. 120 " " 1.4cm, " = 1.5cm, " = 0.93
The largest shells wcrc:-
No. 30 Length = 8.3cm, Height = 5.8cm, L / H r a t i o = 1.43
No. 66 " = 8.4cm, " = 5.7cm, " = 1.47
Figure 10 shows the re la t ionship be tween the I c n g l h / h e i g h i r a t io
and the number of ribs of each shell.
26
2,5 Discussion
Although it was in tended to collect spec imens from all the l ikely
A n a d a r a habi ta ts a round Viti Lcvu, Vanua Lcvu, Ovalau and nearby
offshore islands, [his was jiot ac tua l ly possible, because of several
problems that were encoun te red . Major amongs t these was the
inaccessibi l i ty of trie coast l ine. In many regions the road docs not
follow the coast because the area between the road and the mudf l a t s is
occupied c i ther by extens ive mangroves* p r iva te ly owned p lan ta t ions and
farms, or by Fi j ian villages. In most cases vi l lagers a rc very welcoming
and helpful , but occas ional ly one is r e luc tan t to i n t rude upon their
t e r r i to ry . Thus , the 35 locat ions listed in T a b l e [ do not inc lude nil of
the a reas that the genus inhab i t s , only those t h a t were reasonab ly
accessible to the au thor .
Analysis of Fig, 9 (number of r ibs per shell) shows iwo groups in
the sample - one g roup with between 23 and 28 r ibs , and the o ther group
with between 30 and 38. Herea f te r , these g roups will be iden t i f i ed as
Group A and G r o u p D respect ively .
Refe rence to the da ta in Table I shows tha t spec imens in Group A
came from only 10 of the 35 collect ion sites, name ly , Snwcni Beach,
VVaHoalOfi Beach, Laucalti Point , M a u n i v a t u , V a t u w a q a , Cave Is land, Bcqa,
V u n i d a m o l i , Nnkasa and KLoronatonga, Group B c o n t a i n s spec imens from
nil locations except Va tuwaqa and Wailoaloa.
Analysis of Fig. 10 (shell l e n g t h / h e i g h t ra t ios) shows that in G r o u p
A the ratios vary from 0.89 to 1,43, and in G r o u p 8 f rom 0.09 to 1.60.
27
Within Group A there is an apparent gap in the distribution of these
ratios between 0.98 and 1.03. In Tact 80% of the Anadara collected from
the Vatuwaqa nnd Wniloaloa areas have L/H ratios less than or equal to
0.98.
These two observations led to the hypothesis that Group A might
actually be made up of two different populations. Therefore, it was
decided to test the two possible populations statistically lo sec if ihcre
was any significant difference in their means, i.e.
Population A I sample containing specimens from Wailoalon
and Vatuwaqa.
Population A2 sample containing specimens from Sawcni,
Laucala Point, Maunivntu, Cave Island, Bcqa, Vunidamoli,
Naknsa and Koronatongii.
See Table II in the Appendix (data abstracted from Table I).
Formula
Calculation:-
£ x
n
X
£ X 2
Xl
SOJ
•J
Population A 1
19.41
20
0.9705
18,9429
where t has ( i i j
degrees of
(Parker (1
Popu
+ n2 - 2)
freedom
979)
lation f\Z
28.77
23
1.2509
36J855
30
With this in mind , re-examination of the card ina l area sculpture
pattern shows that pattern (i) is found in Group B, pattern (.ii) in Group
A l and pattern ( i i i ) in Group A2. Also in Group A) the beak is s l ight ly
raised of I' the cardinal area, whereas in Groups A2 and B, the beak is
f la t tened.
Et is interesting to note in Fig. 1J that al though the actual number
of teeth increases w i th age, the number of teeth per mm declines. Growth
of ind iv idual teeth is obviously necessary to give more strength to the
hinge as the valves become heavier. Group B's teeth grow heavier and
larger than ci ther A I or A2.
2.6 Conclusion
The above measurements, calculations and observations suggest i l iat
three species of the genus Anndara may be recognised in (he F i j i
Islands.
SPECIES ONE: (Corresponding to Group B)
This is the most widely d ist r ibuted and the most numerous. The
shell has a pronounced extension of the posterior margin, g i v ing it a
trapczoid shape. This species has radial ribs that number between 30 and
38, although 34 and 35 arc the most common. T y p i c a l l y the anter ior r ibs-
have a median groove, al though the number of ribs exh ib i t i ng such a
feature varies considerably f rom shell to shell. I t was noticed in some o\~
the older shells, that the newer r ib growth towards the shell margin had
median grooves, whereas the older part of the r i b d id not. One or two
f ine striations running parallel to the median groove arc seen in sonic.
31
Periostracum growth is heavy over most of the shell. In the
cardinal area a pattern of fine parallel grooves exists. Live specimens
attach to the soft sandy-mud substrate by a small tuft of byssus,
although there is no byssal gape.
The number of teeth vary too much to be diagnostic, but their
arrangement into two groups is characteristic. The flattened beak is
incl ined to n distance about one-third the way along the hinge from the
anterior end.
This species is probably Anndara antiquata (Area nnlicutata
Linnaeus, 1758). It compares closely with a description of Anndara
antiquata given by Ccrnoliorsky (1971) of shells from the S. W, Pncific:-
"Shcll moderately large, up to 90 mm in length, heavy and
rhomboidal ; posterior sometimes more pronounced in large specimens;
sculptured with somewhat flattened or sl ightly rounded radiating ribs and
concentric striae; the ribs arc cither simple or grooved anteriorly and in
some specimens ribs may have as many as 6 radial grooves on the
anterior margin; the concentric striae are cither confined to the
interstices of the ribs or are continuous. The beaks arc prominent and
recurved, the l igamcntal area is concave, the shell margin fluted and
toothed on the insklc; the hinge line is straight and the small teeth arc
at r ight angles to the hinge tine in the centre but slanting, towards the
extremities. White to creamy-yellow in colour under a thick, dark brown
pcriostracum, l igament blackish-brown, interior of shell white."
31
Pcr ios t racum growth is heavy over most of tlie shell. In the
ca rd ina l area a pa t t e rn oT f ine paral le l grooves ex is t s . Live spec imens
a t t ach to the sof t s andy -mud s u b s t r a t e by a smal l tuf t oT byssus,
a l t hough there is no byssal gape.
The number of teeth va ry too much to be d i a g n o s t i c , but l l icir
a r r a n g e m e n t into two groups is cha rac t e r i s t i c . T h e f la t tened beak is
incl ined to a d i s t ance a b o u t o n e - t h i r d the way a long the hinge from the
an t e r io r end.
Th i s species is p robab ly A n a d a r a a n t i q u a t a (Area anl icuia ta
L i n n a e u s , 1758). It compares closely with a desc r ip t i on of A n n d a r a
a n t i q u a t a given by C c r n o h o r s k y (1971) of shells from the S. W. Pacif ic:-
"Shcfl mode ra t e ly large, up to 90 mm in leng th , heavy and
rhombo ida l ; pos ter ior somet imes more p r o n o u n c e d in large spec imens ;
scu lp tu red with somcwlial f l a t t ened or s l ight ly r o u n d e d r ad i a t i ng ribs and
concen t r i c s t r iae ; the ribs arc e i the r s imple or grooved a n t e r i o r l y and in
some spec imens ribs may have as many as 6 r a d i a l grooves on the
an t e r io r marg in ; the c o n c e n t r i c s t r i ae a r e e i t h e r conf ined lo the
in te rs t i ces of the r ibs or a re c o n t i n u o u s . T h e beaks a r c p rominen t and
recu rved , the l ignmentnl area is concave , the shell marg in f lu ted and
toothed on the inside; the h inge line is s t r a igh t and the small iccih are
at r igh t angles to the hinge l ine in the cen t re but s l an t i ng , t owards the
ex t remi t i e s . White to c r eamy-ye l low in co lour u n d e r a th ick , d a r k brown
pcr ios t racum, l igament b l ack i sh -b rown , in te r ior of shell white ."
32
SPECIES TWO; (Corresponding to Group A ] )
Th is species was f a i r l y common in both the sites f rom which it was
col lected. The shells arc sl ight ly l ighter in weight than those of A ,
anticiuatn w i th an average of 26 ribs ( rang ing f rom 23 to 28), all w i thout
median grooves, but nodulose towards the beak in some. The i r
lcngth:height rat ios arc less than 1.0 resu l t ing f rom their more squarish
shape. Specimens were generally smaller than A. ant iquaia. averaging
about 3.2 cm in length, but the pcr iost racum growth is equally th ick.
The more t r iangular card inal area has very shallow grooves running botl i
paral le l and at r ight angles, to the hinge line. The beak, which is
s l igh t ly elevated above the cardinal area, incl ines to a position that is
just anter ior of centre of the hinge l ine. Teeth arc generally f i ne r than
in A. anticiuata. but their arrangement is s imi lar , Byssus is non-cxisicni,
Th is species is probably Anadara subcrcnata (Lischkc, 1869) as
suggested by Squires c_t a].. (1973). Habc (1965) describes Asubcrcnaja as
fol lows;-
"The shell is i n f l a ted , rounded squarish in shape, and medium-
sized. The surface bears a blackish pcr iostracum. The ribs of I he le f t
valve arc granulated near the summit. Bear about 28 - 32 radial ribs."
SPECIES T H R E E : (Corresponding to Group A2)
T w o major characterist ics have led to the conclusion that a small
number of the specimens collected arc Anadara (Sea phnrcaHnaco nival vis
(Brug ic rc , 1789). A l though they are very s imi lar in shape to A,.
an t ioua tn , the diagnostic characterist ics are: the presence of d ist inct
33
chevron sculpture in the cardinal area, and the unequal size of the
valves which causes the le f t valve to overlap tlie r ight one on the
ventral and posterior margins.
To quote Dodge (1952),
"Areas arc called Scnnhnrca by American paleontologists
The type Seapharea (Gray) , Area inaeouivalvis (Brugicrc), is th in -
shelled, subqunclratc, subcqui latcral , and incqu iva lvc , the Icl'l valve
being larger than the r ight. The cardinal area is very narrow,
except in f ron t of the umbo, where the l igament extends as a
narrow wedge half or less of the distance f rom the umbo to ihe
(interior margin; the remainder of the card inal area in f ron t of the
umbo is elevated and striatc."
and L im (1968)
" four complete and two incomplete ones (chevrons) arc found in
Anndnra (Searcharea) inaequivalvis (Drug,),"
Specimens of this species were collected f r om Laucala Point, Cave
Island, Maunivatu, Beqa, Nakasa and Vun idamol i (on the West Coast Road,
Vanua Lcvu) and Koronatonga in west Natcwa Bay. A l l shells have ci ther
27 or 28 ribs, although most have 28. The teeth arc either in two
unequal blocks - occupying roughly one-third and two-th i rds of ihc
hinge l ine, or, in three roughly equal blocks, Specimens arc generally
less than 5 cm long.
37
3. ECOLOGICAL STUDIES OF ANADAKA A N T I O U A T A IN F IJ I
3.1 Size-frequency distribution and relative abundance of
Anadtira nntinunta in Hie Miuinivatii-Siivn Point areas
of Laucala Bay
3.1.1 Introduction
Located wi th in walking distance of a large indigenous F i j ian
urban population, the intert idal mudflats o f the Maunivatu-Suva
Point arcn have always been popular Tor gleaning act iv i t ies. Low
tide and fair weather brings numerous housewives and young people
to search Tor desirable marine i'ood items. A favour i te has always
been the kaikoso, Anadarn anticuiata. However, been use over the
years the numbers of this species have decl ined, other nmdf ia t
molluscs l ike Gafrar ium. Codakia punctatn and OuidniooKus. and
Pol in ices nidus, have all conic under heavy predat ion.
Mangrove areas f r ing ing the shore have been considerably
reduced in recent years, largely as the result o f ll ic local Ci ty
Council's program to "beautify" the area and enhance its
recreational appeal. Construction of a substant ial sea-wall , and
concrete run-off drains, has grcntly reduced the natural deposit ion
of silt from the adjacent land. However, the Bay as a whole
receives silt from (he Rcwa River system at times o( heavy ra in ant!
subsequent flooding upstream,
The relative abundance and size frequency d is t r ibu t ion of A..
antiouata was monitored over a three year period. Add i t i ona l dnia
has been obtained from previous work by Chanel (1980) and Huilcr
38
(1983) in an attempt to evaluate the population density trends of
Anadara in the area.
3.1.2 Methods
In the second half of three consecutive years (1985-87),
quadrat samples were taken at 10 or 20 m intervals along line
transects 20 m apart extending from shore to the low tide mark.
Each 50 cm square quadrat was thoroughly raked to a depth of
about 10 cm using a small hand-held garden rake. The relative
location of each Anadara was noted and the shell length in cm
recorded.
The site chosen for the investigation was between the sea-
wall opposite Cathedral Secondary School and the North Light
Beacon. This was considered to be representative of the whole
muciriat area, i.e. substrate of sand/silt mix, numerous shallow pools
of standing water, supporting lush growth of the sea grasses
Svringodium isoctifolium. Halodule uninervis and Halophila ovalis.
At high tide the mudflats arc covered to a depth of about 1.5
m by water. Offshore is a deep channel used by small craft, and
further out, an ^extensive coral reef protects the mudflats from the
open sea (Fig. 14). Sampling sites arc shown on Table IV in the
Appendix.
41
3.1.4 Discussion
The table below (Fig. 15} summarises the infor-mation gained
on the density of Anadara on these mudflats. Figure 16 shows the
size-frequency distributions for 1980 and 1985. (Note: Cliand's
1980 results from a similar survey carried out in the same area arc
included for comparison.) The 20-spccimen sample in the 1985
survey is too smnll to make generalisations. However, the pattern
of size frequency distribution in both years show the same trends,
i.e. most specimens are between 2 and 5 cm in length.
Review of the summary table shows that there is a large drop
in standing crop between July 1985 and August 1986, One possible
reason for this is that early in 1986 three tropical cyclones hit the
area and torrential rains caused massive flooding of the Rcwa River
system. Tidal water in Laucala Bay was loaded with brownish-
orange silt, as far out as the reef, for several days. This left a
noticeable deposit of silt all over the mudflats, which probably badly
affected the filter-feeding molluscs. Additionally, the storm
conditions produced waves that caused great mechanical agitation of
the sandy-mud substrate, shifting it and dislodging its inhabitants .
Large numbers of dead bivalves and gastropods were left lying on
the surface. By August the dead shells had been washed nwny or
buried by normal tidal action, but the number of live Anadara found
was very few. Two hours of continuous sieving with a 2 mm gauge
sieve in likely places yielded no spat. By September 1987 the crop
had not recovered.
44
Chnnd (1980) took 30 samples from each of 15 transects nt 2 m
intervals on the Maunivatu mudflats, Each sample sieved came from
a 30 cm x 35 cm rectangle. Therefore the total area of the
samples was 30 x 15 x 1050 = 472,500 cm2. This is approximately
47 m^ From this 47 m^ he collected 123 Anadnra, i.e. 1/0.4 m ,
which is considerably more than the 1/1.6 m , five-and-a-half yenrs
later.
The general comment from the people gleaning in the area is
that it now takes them much longer to find a few smnll ones
compared with the time it took them to collect a lot of big ones,
in the "old days".
Unfortunately nothing seems to be known about the recruitment
of Anadara in this area. It is possible tliat the larvae arrive in
currents from other parts of the Bay or further afield, in which
case, given that gleaning activities arc not too intensive, the
Andarn populations in this area could recover. However, if ihc
existing adults are responsible for the rcgene-ration, then it is
possible that they are not present in sufficient numbers to maintain
the necessary fecundity levels to maintain the population.
3.2 Seasonal gonad states in Anadara antiouata
3.2,1 Introduction
Many tropical marine species reproduce all year round as
there is no particular ecological advantage or disadvantage
associated with any one part of the year (McConnaughcy, 1978).
45
This study was carried out to determine whether or not there is
any seasonally associated with gonad activity in the Anadnra
antiouata inhabiting the soutli-eastern part of Viti Lcvu.
3.2.2 Method
Microscopic examination of the gonad tissue established thai
the cream coloured tissue was tcstis and the orange coloured tissue
ovary,
A basket of fresh A, nnticiuata was obtained from the Suva
Municipal market at the end of the second week of each month,
over a period of one year. Because these animals were all collected
from the Nnmnra area of Tailevu, they were all part of the same
population. Out of each basket, 15 Anadara were randomly selected
in each of the following size-classes:
32 - 37 mm, 38 - 43 mm, 44 - 49 nun, 50 - 55
mm and 56 - 61 mm.
Each animal was then opened with a knife and the colour of
its gonad recorded as "orange", "cream" or "noi developed".
(Occasionally the desired sample of 15 was not available for each
size-class.)
3.2.3 Results
The counts for the gonad state in each size-class arc shown
in Fig. 17 below.
49
Size-class maturity rates did not seem to d i f f e r g rea t ly from
the total sample frequencies; in most cases the n u m b e r s were s imply
a reflection of the overall rate. However , it is noted tha t th is
investigation did not include juveniles and small a d u l t s , i.e. those
less than 32 mm in length, and it is possible t h a t this g r o u p may
show a d i f fe ren t maturity pat tern.
&.
51
As in F i j i , the S. E, Trades cover the area from Apr i l to September
and the N, E. Trades bring unstable convergence zone weather between
November and March. Temperatures generally exceed 20°C with
substantial rainfal l throughout the year, although September through
March is the hottest and wettest time, All groups are influenced by the
South Equatorial ocean current throughout the year.
Geologically, the islands arc a mixture of volcanic and limestone
material (Derrick, 1951} and many have f r ing ing and/or barrier reel's.
Atolls are common, as arc lagoons. Only the higher, larger volcanic
islands have rivers with volumes sufficient to support the development of
mangrove forests and their associated mudflats which arc the likely
habitats of Anadnra. However, occasionally low-lying islands offer
alternative habitnts, in more sandy locations. Some island shorelines
enclose raised limestone shelves that have become covered with f ine-
ground, powdery sand that supports beds of sea grass, as in the
Nga'unaha lagoon in Vava'u. Other islands have shallow, sandy-bottom
lagoons that are protected from the f lushing action of the tide by sand
bnrs, e.g. the Asau lagoon in Savai'i,
A,2 Method
Each island group was surveyed to determine the distribution of
Anadara species. Where stops were possible, Ana darn shells were
collected from the beaches and mudflats, and marked for further study.
Accessibility of sampling sites was . constrained by local roads and
shoreline topography.
52
Topographical notes were recorded at each of the sampliiig site.
Subsequent morphomctric measurements of Anndara enabled
comparisons to be made with those found hi Fiji.
4.3 Vanuatu
Specimens were collected from three islands in the Vanuatu group:
Efatc, Espiritu Santo and Malckula. Each of these islands is constructed
of volcanic and raised limestone material. Rivers carry sediments to the
coast and mangrove swamps occur in patches. Shallow sandy bays arc
fairly common between headlands and away from river mouths.
Fig, 21 shows the collection sites and relevant geographic data:
56
Data from the table shows that the specimens collected in Vanuatu
form a fa i r ly homogeneous group. The length;height ratios vary f rom
1.05 to 1.48, with n median of 124, This ratio is lower than the
average (1,32) for A. antiourtta investigated in F i j i , and is reflected in
their slightly squarcr shape (see Fig. 22).
The number of ribs varies from 30 - 37, but the mean is 33
compared wi th 34/35 in the F i j i specimens. Many shells had median
grooves on the anterior ribs and some had as many as 10 very f ine, but
clear parallel striat ions running down the ribs, A l l specimens had the
some type of sculpture in the chevron area as the F i j i A. nnt iquata and
the teeth were simi lar ly arranged into two groups.
It would seem, therefore, that the Anadara collected from Vanuatu
were ail A. anticuiata w i th very slight variations in shape and mean r ib
number, when compared wi th those found in F i j i .
Although no other species of Anadara were found in the areas
investigated it is acknowledged that only a small section of the Vanuatu
group was included in this survey.
60
Analysis of the specimens collected in Western Samoa is shown on
Table VII in the Appendix.
Seven sites were investigated on Tutuila, a very rugged island with
a rocky shore line. Despite this rough terrain some quiet sheltered bays
do exist and mangroves are present wlicrc one might expect to find
Anadara, However, specimens were found at only 2 locations.
At Vatin, about 1 km past the canneries in Pago Pago Harbour, a
pile of old shells was found on the beach amongst the rocks and rubble,
Possibly these had been dumped here after a meal of the shellfish which
had been imported from Western Samoa. Several shells were collected,
but been use their origin is in doubt, their measurements have not been
included in Table VII,
Similarly, the origin of an old Anadara shell found on the roadside
at Utulci Beach Park in Pago Pago, is doubtful, It mny have been
dredged up with other harbour deposits to be used as road-fill.
At Pala Lagoon on the northern side of the island, the bay is
enclosed by an extensive sand-bar. Mangroves grow along ihc foreshore
and the substrate of the lagoon is sandy-mud. Although large Ga("ranurn
and mussels were found here, no Anadara were to be seen.
The data shown in Table VII shows that the Samoan specimens arc
almost identical to the A. antiauata of Fiji. Although the sample is
fairly small, the lcngth:height ratio is very similar, being 1.39 (Fiji
5. CONCLUDING SUMMARY TO THE STUDY PROJECT
As a result of this study, 1 conclude that:-
1. There arc three species of Anadara present in F i j i ; A..
antinuata ( L i n , 1758), A, subcrcnatn (Lischke, 1869) nncl
A. incanuivnlvis (Brugicrc, 1789). Of these A. ant iouatn
is the most common.
2. In the Suvn Point-Maitnivatu area of Laucala Bay Anadara
are d imin ishing in both numbers and average size.
3. in S.W. V i t i Lcvu, reproductive act ivi ty in A. anticuuna
reaches a peak during the hot, wet season, and shows a
period of relat ive inact iv i ty during the cooler months.
4. That only one species of Anadara has been found in
Samoa and Tonga, which is A. antiouatti (L in , I75S), and
that a more extensive survey of Vanuatu is needed to see
if other species exist there.
69
6. REFERENCES
Alexander, R,M. 1979. The Invertebrates. Cambridge University Press.
Barnes, R..D. 1980. Invertebrate Zoology (4th Edition) Holt-Saundcrs
International Editions. Japan,
Broom, M.J. 1983, Gona<l development and spawning in Anndara arnnosa (L).
Aquacufturc 30: 21 1-219.
Broom, M.J. ]985. The biology and culture of marine bivalve molluscs of the
genus Anadara, ICLARM Studies and Reviews, No. 12.
Butler, A.J. 1983, A preliminary examination of populations ol" ihc Kai-koso
Anadara cornea (Reeve) near Suva, Fiji, A report to the IMR,
University of the South Pacific.
Ccrnohorsky, W.O. 1971. Marine shells of the Pacific. Vol. If. Pacific
Publications, Sydney.
Cliand, B. 1980. Research on Anadara around Suva coast. Manuscript report
to IMR, USP, Fiji.
Derrick, R.A, 1951, The Fiji Islands - a geographical handbook. Government
Press, Suva, Fiji.
70
Dodge, H. 1952. An historical review of the molluscs of Linnaeus. Part 1.
Bull, of the American Museum of Nat. Hist., N.Y. Vol. 100, An , I.
Emerson, W,K. and M.H. Jacobson, 1976. The American Museum of Natural
History guide to shells - land, freshwater and marine. Alfred A. Knopf.
N.Y.
Gludc, J,B. 1972. Report on the potential for shellfish aquaculuirc in Palau Is.,
Yap Is,, Guam, Truk, Ponapc, Ell ice Is., American Samoa, Cook, Is., Fiji
Is,, New Caledonia and French Polynesia. FAO Fl : SP/SOP RED. 102/S.
Ha be, T. 1965, Shells of the West Pacific in colour. Vol. I (2nd Edition)
Hoikusha Publishing Co., Osaka,
Kennedy, T.F. 1966. A descriptive atlas of the Pacific Islands. A.H. and A.W.
Reed, Wellington, New Zealand.
Lewis, A.D. 1986. Aquatic Foods of Fiji. A poster produced by Fisheries
Division, Ministry of Primary Industries, Govt, of Fiji.
Lim, C.F. 1968, A rc-appraisal of the sub-genera of Anndnra. Proc. of the
Symposium on Mollusca. Cochin, India, Scries 3; 61-74.
McConnaughcy, B.H. 1978. Introduction to Marine Biology (3rd Edilion). C.V.
Mosby Co. St Louis.
71
Morton, J.E. and U. Raj. 1983. The shore ecology of Suva and S. Viti Lcvu.
Manuscript folio, IMR, USP, Fiji,
Navnkalomana, J. 1982. Fiji. Proc. Bivalve culture in Asia and the Pacific
Workshop. Singapore. IDRC. Asia Regional Office, Singapore.
Parker, R.E. 1979. Introductory Statistics for Biology (2nd Edition), Edward
Arnold, London,
Parkinson, B.J. 1982, The specimen shell resources of Fiji, Report to South
Pacific Commission and Govt, of Fiji, SPC, Noumea, New Caledonia.
Rabanal, R.H., S.T. Cnvuilati and F. Mate, 1981. The development of
aquaculture in Fiji. FAO report to Govt. of Fiji. FAO Regional Office
for Asia and the Pacific. Bangkok, Thailand.
Spcnncmnnn, D.H.R. 1987. Availability of shellfish resources on prehistoric
Tongatapu, Tonga : effects of human predatioii and changing environment.
Archaeology in Occana, Vol. 22, No. 3.
Squires, H,J., D. Carlson, T.P. Ritchie and N. Gundcrmann. 1973. Shellfish on
ncarshorc fishing grounds at Wailoloa Beach. Nadi, Fiji. Agr. J. M= 71-
74.
72
Ting, Y.Y., S. Kasahara, and Nakamura, 1972. An ecological study of the so-
called Mogai (Anndara subcrennta (Lischke)) cultured in Kasaoka Bay,
Journal of the Faculty of Fish, and An, Husbandry. Hiroshima
University. U.: 91-1 10.
Uwate, K.R. and P. ICunatuba, B. Roabati and C. Tcrakanoi. 1984. A review of
aquaculturc activities in the Pacific island region. Pacific Islands Dcv.
Program. E-W. Centre, Hawaii.
Wolff, W.J., A. Gucyc, A. Mcijboom, T. Picrsma and M.A. Sail. 1987.
Distribution, biomass, recruitment and productivity of Anrtdnra scnilis (L.)
on the Bane d'Arguin, Mauritania. Netherlands J. of Sea Research.
2JL0): 243-253.
Yoloye, V, 1974. The sexual phases of the West African bloody cockle
Anadara scnilis (L,). Proc. Mnlncol, Soc. London. 4_L: 25-27.
/? Zann, L.P,, L. Bell and T, Sau. 19S4a, A preliminary survey of the inshore
fisheries of Upohi Is., W, Samoa. IMR, USP, Fiji and Fisheries Div,
Dcpt of Ag. and Fish,, W. Samoa.
Zann, L.P., W.J. Kimmcrcr and R.E. Brock, 1984b. Ecology of F a n g n ' u t a
Lagoon, Tongatapu, Tonga, Sea Grant Co-op Report. UHIH1-SEAGRANT
CR, 84.04.
73
7. APPENDICES
TABLE I ; Measurements and calculations relating to the Anaclarn
specimens collected from the Fiji Islands
TABLE II : Data for statistical analysis of Populations A] and A2
TABLE III: Data for representative samples of A|, AT and B, to show
relationship between shell length and shell height on a log
scale for each group (Figure 12)
TABLE IV: Distribution of quadrat sampling sites along transects in
the Maunivatu-Suva Point area
TABLE V : Gonad state counts for A. nnticiuata. converted to
percentages
TABLE VI: Analysis of Anadara specimens from Vanuatu
TABLE VII Analysis of Anadara specimens from Samoa
TABLE VIII: Analysis of Anadnrn specimens from Tonga
88
8. .ACKNOWLEDGEMENTS
It is with great pleasure that 1 record my sincere appreciation to
Dr Alison Hayncs for her continual support and encouragement, practical
guidance and good humour throughout the course of this project.
Also, I should like to thank Drs C. .1. Webb and L. P, Znnn for
their help in in i t ia l ing the project; the USP Research Committee I'cir
funding; Dr W. Kcnchington for assistance with the f ina l presentation
and Mrs Prcm L. Kumar for her expert typing of the thesis.