SCI. MAR., 61 (Supl. 2): 99-107
SCIENTIA MARINA
1997
ECOLOGY OF MARINE MOLLUSCS. J.D. ROS and A. GUERRA (eds.)
Endosymbionts of mangrove oyster in nature
and under cultivation*
V. K. MACHKEVSKY
Department of Ecological Parasitology, Institute of Biology of Southern Seas, Nakhimov Av.2,
Sevastopol, Crimea, Ukraine 335011.
SUMMARY: Mangrove oyster Crassostrea tulipa assemblages on mangrove air roots and raft collectors were investigated at the Tabounsu Estuary (Kaloum Peninsula), Konkoure Estuary and rock shore at the Rogbane Village (Republic of
Guinea-Conakry). The conditions in this assemblages were distinguished, first of all, by the duration of immersion time. A
total of 13 endosymbiont species (parasites and endocommensals) were recorded. There were 6 species of parasites: Aspidogastrea (1), Trematoda (3), Nematoda (1), Protozoa (1), and 7 species of endocommensals: Turbellaria (3), Polychaeta
(3),Crustacea (1). The essential factors influencing the formation of the endosymbiont fauna of oysters are: stability of biocenotic relations and the period which oysters spend without water. In natural assemblages the fauna of endosymbionts
changed with depth and was most numerous at the low levels than at the high ones. The maximum number of species (10)
was observed at the natural oyster assemblages. The oysters at the floats were invaded by 4 species only, but their quantity
was 9-162 times more numerous than in natural assemblages. Some species of endosymbionts which are harmful for human
health and oyster culture were revealed.
Key words: Mangrove oyster, ecology, cultivation, parasites, endocommensal, West Africa.
RESUMEN: ENDOSIMBIONTES DE LA OSTRA DE MANGLAR EN LA NATURALEZA Y EN CULTIVO. – Se investigaron poblaciones de
la ostra de manglar, Crassostrea tulipa, en raíces aéreas de mangles y en bateas de cultivo en el estuario de Tabounsu (península de Kaloum), en el de Konkoure y en la costa rocosa de la aldea de Rogbane (República de Guinea-Conakry). Las condiciones en estas poblaciones se distinguieron, ante todo, por la duración del tiempo de inmersión. Se registraron 13 especies endosimbiontes (parásitas y endocomensales); 6 especies parásitas: Aspidogastros (1), Trematodos (3), Nematodos (1),
Protozoos (1), y 7 endocomensales: Turbelarios (3), Poliquetos (3), Crustáceos (1). Los factores esenciales que influyen
sobre la fauna de endosimbiontes de las ostras son la estabilidad de la relaciones biocenóticas y el período que las ostras
pasan fuera del agua. En las poblaciones naturales, la fauna de endosimbiontes cambió con la profundidad, y era más numerosa en los niveles inferiores que en los superiores. El número máximo de especies (10) se observó en las poblaciones naturales de ostras. Las ostras de las bateas estaban invadidas por sólo 4 especies, pero éstas aparecieron en abundancias 9-162
veces más numerososas que en las poblaciones naturales. Se descubrieron algunas especies de endosimbiontes que son perjudiciales para la salud humana y la ostreicultura.
Palabras clave: Ostra de manglar, ecología, cultivos, parásitos, endocomensal, África occidental.
INTRODUCTION
The mangrove oyster Crassostrea tulipa is a
dominant mollusc species in mangrove estuaries of
Western Africa. It forms a peculiar biocenosis,
*Received October 1995. Accepted October 1996.
girdling by continuous strip line the air roots of
mangrove trees, coastal rocks and stones. Many
invertebrates and fish hide themselves and find the
food on mangrove oyster assemblages. Under low
tide the nearwater birds live at the mangrove littoral.
Owing to high- and low tidal dynamics of water
level in mangrove oyster estuaries the assemblages
are exposed to periodic emersion from 4 to 8 hours.
ENDOSYMBIONTS OF MANGROVE OYSTER 99
Mangrove oyster is the traditional object of
catch. In recent years its cultivation has been undertaken (Kamara, 1982). The technology of cultivation of C. tulipa in Guinea-Conakry is developed
and successfully examined by Morozova and
Machkevsky (1991), among others. Consequently,
the endosymbiont fauna composition and character
of its forming are very interesting not only for fundamental science but for applied science.
MATERIAL AND METHODS
This report is based on data gathered from material received by the author during a two years (19891991) study of the biology and endosymbionts (parasites and endocommensals) of C. tulipa in natural
and artificial oyster assemblages on mangrove roots
and float collectors at the Tabounsu and Konkoure
Estuaries and on rocky shore at the Rogbane Village
(Republic of Guinea-Conakry). A total of 2000 individuals of oyster were examined. Common hydrobiological and parasitological methods were used.
RESULTS
The brief descriptions and localities of endosymbionts are given. The data on C. tulipa endosymbionts are presented for the first time, and not all of
them are identified to species level.
Parasites:
1. Protozoa.
1.1. Myxomyceta (Sarcomastigophora?) (Fig.1).
The yellow “tumors” on the ligament and in the
under-top shell surface are revealed in oysters. Host
sizes: 62-90mm. Ligament was destroyed to a
greater or lesser degree. The content of the “tumor”
was a thick liquid. The smear of it appeared as a
mass of diverse cells. Among the cells were
observed structures with several appendixes and
nuclei. These structures make these organisms look
like microsporidian plasmodia (Ginetsynskaja and
Dobrovolsky, 1978). However, molluscs are unusual hosts for microsporidians.
Locality: Tabounsu Estuary, natural and artificial
oyster assemblages on mangroves and on the floats
of the experimental hatchery. Location: the inner
surface of ligament and under-top area of shell
100 V.K. MACHKEVSKY
FIG.1. – Myxomyceta (Sarcomastigophora?). a, "tumor" on the
ligament and shell; b, several plasmodia.
(more often on right valve). Intensity of infection:
usually one, rarely two formations (one of them on
ligament, another below, inside the shell). Prevalence: 0.1-16.2 %, independent of environmental
conditions.
As a result of experimentation, it was shown, that
parasites reduce host resistance to unfavourable
environmental conditions. Among the oysters
placed in stews on growth, one third perished. Dead
oysters (80%) had “the disease of ligament”.
This parasite is very dangerous for oyster culture,
causing diseases of this mollusk and adding a disgusting odour to oyster meat.
2. Aspidogastrea.
2.1. Lobatostoma (ringens?), juv. (Aspidogastrida)
(Fig. 2).
Locality: Tabounsu and Konkoure Estuaries, natural assemblages of oysters on mangrove roots. Host
sizes: 54-91 mm. Location: the wide channels of
hepatopancreas. Intensity of infection: 1. Prevalence: 3.1 %.
Based on morphological signs and sizes these
aspidogastreans are close to Lobatostoma ringens
(Linton, 1907) Eckman, 1932. Sexually mature
worms were found in the intestine of fish (pompano,
Trachinotus maxillosus) in coastal waters of northwestern Africa (Szuks,1982).
3. Trematoda.
FIG. 2. – Lobatostoma (ringens?), juv. (Aspidogastridae). a, external aspect; b, anatomy.
3.1. Echinostomatidae gen.sp. mtc. (Fig. 3).
Locality: Tabounsu and Konkoure Estuaries, natural mangrove assemblages. Host size: 57-70 mm.
Location: hepatopancreas. Intensity of infection: 27. Prevalence: 2.8 %. The definitive hosts of this
trematode may be littoral sea birds: herons and sandpipers having the access to oyster assemblages during a long time due to low-tidal emersion of mangrove roots. The potential host of parthenogenetic
generations is the gastropod Littorina angulifera. It
is invaded up to 60% by sporocysts with the echinostomatid cercariae. These gastropods inhabit
mangroves above the oyster assemblage, and are a
usual component of mangrove malacofauna.
This parasite may be dangerous for public health,
because echinostomatids are known as human parasites (Skrjabin and Bashkirova , 1956).
3.2. Stephanostomum gen. sp. mtc. (Acanthocolpidae) (Fig. 4).
Locality: Tabounsu Estuary, oysters of natural
mangrove assemblages. Host sizes: 55-61 mm.
Location: the bases of gills. Intensity of infection: 1.
Prevalence: 0.5 %. For the first time C. tulipa is reg-
FIG. 3. – Echinostomatidae gen. sp. mtc. a, total view; b, adoral
disc with hooks, face view; c, the same, dorsal view; 1, oral sucker; 2, acetabulum; 3, terminal glands; 4, intestine; 5, flame cells of
excretory system; 6, excretory sack with branches.
FIG. 4. – Stephanostomum gen. sp. mtc.(Acanthocolpidae), metacercaria in cyst (indications as in Fig. 3).
ENDOSYMBIONTS OF MANGROVE OYSTER 101
3.3. Opecoelidae gen. sp. mtc. (Opecoelidae) (Fig. 5).
Locality: Tabounsu Estuary, oysters of mangrove
assemblages. Hosts size: 48-55 mm. Location: the
mantle connecting tissue. Intensity of infection: 1-2.
Prevalence: 5.0 %.
The definitive hosts of opecoelid trematodes are
fish, eating oysters.
4. Nematoda.
FIG. 5. – (Opecoelidae), metacercariae. a, in cyst; b, total view (indications as in Fig. 3).
istered as additional host for trematodes of the genus
Stephanostomum. Probably the definitive hosts of
hermaphroditic generation of this parasite are fish
from the coastal zone, eating oysters. Usually at the
waters of Guinea the metacercariae of Stephanostomum were found in fish (Najdenova, 1988).
4.1. Echinocephalus sinensis (Gnathostomatidae), l.
(II stage) (Fig. 6)
Locality: Tabounsu Estuary and Konkoure Estuary, natural oyster assemblages. Hosts size: 41-53
mm. Location: hepatopancreas. Intensity of infection: 1. Prevalence: 2.5 %. E. sinensis is known as a
parasite of the Pacific oyster Cassostrea gigas (Ko,
1974). Maximal invasion of the oysters by this parasite is known in Hong-Kong region. The definitive
host of this nematode is the ray, Aetobatus flagellum
(Ko, 1975). Ko et al. (1975) and Ko (1976, 1977)
indicated that larvae of E. sinensis survive in the
stomach-intestine tract of kittens and rhesus monkeys, causing patological changes.
This parasite has possible importance for public
health as a potential illness agent.
FIG. 7. – Acoela fam. sp. Total view.
Endocommensals:
1. Turbellaria.
FIG. 6. – Echinocephalus sinensis l. (II stage) (Gnathostomatidae).
a, excysted larva, total view; b, anterior region, lateral aspect; c, en
face view; d, cephalic hook.
102 V.K. MACHKEVSKY
1.1. Acoela fam. sp. (Fig. 7).
Locality: Tabounsu and Konkoure Estuaries,
mangrove, rock and artificial oyster assemblages.
Host sizes: 30-91 mm. Location: the mantle cavity,
external epitelium surface of mantle, gills and
methasome. Intensity of infection: 10-50. Preva-
lence: 9.0 % (rock assemblage); 19.0 % (mangrove
assemblage); 90.0 % (artificial assemblage).
These turbellarians are the most mass endosymbiont species of mangrove oyster. Their distribution
in oyster assemblages is irregular.
This species would be important for oyster culture under unfavourable environmental conditions.
FIG. 8. – Rhabdocoela fam. sp.1. Total view.
1.2. Rhabdocoela fam. sp.1 (Fig. 8).
Locality: Tabounsu Estuary, mangrove and artificial oyster assemblages on floats. Host size: 48-53
mm. Location: the mantle cavity. Intensity of infection: 1. Prevalence: 0.1 % (mangrove assemblage);
0.1 % (artificial assemblage).
FIG. 10. – Polydora (ciliata?) (Spionidae). a, shell with blister
pearl (1); b, caudal part; c, cephalic part.
FIG. 9. – Rhabdocoela fam. sp. 2. Total view.
1.3. Rhabdocoela fam. sp. 2 (Fig. 9).
Locality: Tabounsu Estuary, mangrove and artificial oyster assemblages on floats. Host size: 47-55
mm. Location: the mantle cavity. Intensity of infection: 1. Prevalence: 0.1 % (mangrove assemblage);
0.1 % (artificial assemblage).
2. Polychaeta.
2.1. Polydora (ciliata?) (Spionidae) (Fig. 10).
Locality: Tabounsu and Konkoure Estuaries,
mangrove and artificial oyster assemblages. Host
size: 51-105 mm. Location: shell. Intensity of infec-
tion: 1-8. Prevalence: 0.7 % (mangrove assemblage), 61.0 % (artificial assemblage).
As a rule, P. (ciliata?) penetrates into the oyster shell in the under-top area, where the shell is
most massive. At an inital invasion stage a single
polychaete gets into the shell. Its refuge is reflected by the contrast color stains and lines. Then a
driller perforates the shell hypostracum and penetrates into the extrapalial cavity of host. As a
result of this interaction a blister pearl is formed
by the mollusc (Fig. 10a), which gives harbour for
P. (ciliata?). Further on the cavity of the blister
pearl is filled by silt. Not only new individuals of
P. (ciliata?) live here, but other invertebrates. The
blister pearl reduces largely the capacity of extrapalial and mantle cavity of invaded oyster.
Mechanical effect on the soft tissue of host and
redistribution of the host resources under invasion
takes place.
This species is dangerous for oyster culture as an
agent decreasing the oyster growth rate and damaging the quality of oyster as food product.
ENDOSYMBIONTS OF MANGROVE OYSTER 103
FIG. 11. – Eulalia sp. (Phyllodocidae). a, shell with blister pearl (1);
b, cephalic part; c, caudal part.
FIG. 12. – Nereidae fam. sp. a, shell with blister pearls. 1, Nereidae
fam. sp.; 2, Polydora (ciliata?); b, cephalic part; c, caudal part.
2.2. Eulalia sp. (Phyllodocidae) (Fig. 11).
Locality: Tabounsu Estuary, artificial oyster
assemblages on the floats. Host size: 64-74 mm.
Location: shell, blister pearl. Intensity of infection:
1. Prevalence: 1.0 %. This species, known as freeliving, has no ability to perforate hard substrates. It
inhabits blister pearl after P. ciliata (?). Probably it
is the second commensal.
2.2.3. Nereidae fam. sp. (Fig. 12).
Locality: Tabounsu estuary, artificial oyster
assemblages on floats. Host size: 65-70 mm. Location: shell, blister pearl. Intensity of infection: 1.
Prevalence: 0.8%. Probably it is the second commensal.
2.3. Crustacea (Arthropoda).
2.3.1. Pinnotheres larissae Machkevsky, 1992 (Pinnotheridae) (Fig. 13).
Machkevsky (1992) gives a detailed description
of this species.
104 V.K. MACHKEVSKY
FIG. 13. – Pinnotheres larissae (Pinnotheridae); a, female; b, male.
FIG. 14. – Seasonal variability of P. larissae prevalence: (y, prevalence, %; x, months).
Locality: Tabounsu Estuary, mangrove and artificial assemblages and Rogbane Shore, rock natural
oyster assemblages. Host size: 60-74 mm. Location:
mantle cavity, under mantle hood. Intensity of infection: 1. Prevalence: 0.6% (mangrove assemblage),
3.5% (rock assemblage), 23.0% (artificial assemblage on float).
The pea-crabs appeared to be the biggest oyster
endocommensals. Their weight is 5-20 % of host
weight. By the keen pereiopod dactyluses they obviously trap their hosts and feed a considerable part of
food of host. The structure and number of the crab
population shows seasonal changes (Fig. 14).
This large size endocommensal may be an undesirable element in oyster culture.
DISCUSSION
We inspected three typical oyster assemblages:
natural ones on mangroves and rocks, and artificial
ones on floats of experimental plantation. Each of
these had similar and different biotopical characteristics. Likeness permited us to conclude that
both assemblages were formed as dense brush on
hard substrate. Differences permited us to conclude
that the most high density of oyster assemblages
per unit of water volume was on mangroves and
floats. The more important ecological factor was
that the rock and mangrove assemblages have
drained during outflow twice per day. Exposure to
FIG. 15. – Vertical variability of mangrove oyster assemblage and
some endosymbionts parameters depending on depth: a, oyster
size: left y,oyster number; right y, depth levels (1, 13 cm; 2, 26 cm;
3, 26 cm; 4, 26 cm); x, oyster size (mm); b, density of oyster settlement (y, depth levels; x, oyster number); c, number of species of
endosymbionts (y, depth levels; x, species number, %); d,
prevalence of Acoela fam.sp. (y, depth levels; x, prevalence, %).
air is 4 to 8 hours dependent on the oyster assemblage position above a depth of 0 m. The emersion
factor is the main factor and causes other factors
for ecosystem assemblages: overheating, anoxibiotic metabolism, decrease of filtration activity and
intensity of feeding, decrease of the growth rates
and the time of oyster contacts with environment.
Owing to the effect of these ecological factors oyster assemblage on mangrove air roots has a spindle
shape. We distinguished four levels of this assemblage differing by some signs (fig. 15a). The first
level is exposed longer to air and oysters here are
not numerous and are smallest (Fig. 15a,b). The
second level is deeper, the density of assemblage
and oysters individual sizes are increased. The
third level is where assemblage density and oysters
individual sizes reach maximum. For the main part
of the fourth level the oyster quantity and size are
sufficiently high, but in the last region of the level
ENDOSYMBIONTS OF MANGROVE OYSTER 105
they sharply decrease, in spite of the fact that oysters there are out of water for the least time. Environmental conditions for oysters may not be
favourable here. For example, this region of assemblage is subjected to the silt effect more than others. At the floats in total underflow immersion
regime these conditions for oysters are absent. As
a consequence of these differences we have
observed differences in endosymbiont fauna.
The oyster assemblages on mangroves are the
most representative and a considerable component
of the estuarine ecosystem. It was there that we
observed the most multicomponent endosymbiont
fauna (Fig. 16a). The endosymbionts of the vertical
oyster assemblages are disposed irregularly (Fig.
15c). The major ecological factor is tidal water
dynamics and connected with it littoral emersion
effect. The oysters from different levels of assemblages are able to remain out of water more or less
time, switching over to anaerobic metabolism and
to undergo an increase of temperature to 40ºC. On
the highest level, closed to the water surface, we
have recorded only endocommensals (Acoela fam.
sp.). The endosymbiotic organisms dependence on
theirs hosts to a too high degree appeared with an
increase of depth (Fig. 15c). All parasites were registered in the lower part of assemblage, less
exposed to air. Given that the host-parasite relationships are more antagonistic than the relationships between hosts and endocommensals, the
infected oysters did not bear long-time emersions
and perished first. Among the three of mass endocommensal species the most steady to emersion is
the turbellaria Acoela fam. sp. This species inhabits all levels of the oyster assemblages, but numbers decrease in proportion to emersion time, i.e.
from the lower to the upper part (Fig. 15d). Probably, the crab P. larissae and polychaeta P. ciliata
are not able to resist anoxibiosis and avoid overheating. Therefore it is possible that they are
recorded only on lower assemblage levels.
The oyster endosymbiont fauna in natural rock
assemblages in the open estuary was investigated.
From 13 species found on estuarine mangroves only
three endosymbiont species were found here: Myxomyceta (Sarcomastigophora?), Acoela fam. sp. and
P. larissae (Fig. 16b). Probably the mangrove estuary zone has a higher biodiversity and complexity of
conditions, facilitating the dispersion of invading
endosymbiont larvae.
Artificial oyster assemblages on floats situated
near the mangrove do not undergo periodical emer106 V.K. MACHKEVSKY
FIG. 16. – Occurrence of endosymbionts in different settlements of
C. tulipa: a, float collectors; b, rocks; c, mangroves (y, prevalence,
%; x, endosymbiont species): 1, Myxomyceta (Sarcomastigophora?); 2, Lobatostoma (ringens?), juv.; 3, Echinostomatidae gen. sp.
mtc.; 4, Stephanostomum gen. sp. mtc.; 5, Opecoelidae gen. sp.
mtc.; 6, Echinocephalus sinensis l. (II stage); 7, Acoela fam. sp.; 8,
Rhabdocoela fam. sp. 1; 9, Rhabdocoela fam. sp. 2; 10, Polydora
(ciliata?); 11, Eulalia sp.; 12, Nereidae fam. sp.; 13,
Pinnotheres larissae.
sion and exist for a relatively short time period: 6-8
months. Endosymbiont fauna of float assemblages
consists only of organisms which have a direct life
cycle: protozoans, turbellarians, polychaeta and
crabs (Fig. 16c). This supports the view that simple
parasitic systems are able to expand on young
ecosystems of artificial reefs (the oyster floats
belong to such systems) to a greater degree
(Gaevskaja and Machkevsky, 1995). The absence of
periodic emersion of floats removes such problems
as overheating and anoxibiosis The contact between
endosymbionts and their hosts are not broken under
these conditions. Therefore the number of endosymbionts in oyster assemblages on floats increases in
number. The prevalence of endosymbionts of oyster
assemblages on the floats as compared with that on
mangrove assemblages is greater: protozoa Myxomyceta (Sarcomastigophora?), 162 times; turbellarian Acoela fam. sp. 9x; polychaete P. ciliata, 87x;
crab P. larissae, 38x.
The ecological factors influencing the occurrence of endosymbiont fauna are specific and
depend on different factors. One of them is the size
of the host. The first endosymbionts (turbellarians)
inhabit the young oysters when they are one month
(3 cm long). Three-month old oysters give harbour
to protozoa, polychaeta and crabs. This may be
explained by the fact that turbellarian sizes does not
limit their vital space in young oysters. Crabs and
polychaeta can have sufficient living space only in
large oysters.
The lifespan of oyster assemblages is also an
important ecological factor. Trematodes and nematodes, having complex life cycles, have not enough
time for contact with their potential hosts at the float
assemblages.
This work does not give full answers to all questions. Many factors affecting endosymbionts in oyster assemblages (natural and artificial) are connected with the biological and ecological characteristics
of endosymbionts and need further investigation.
REFERENCES
Angel, G.A. – 1986. The Biology and Culture of Tropical Oysters.
Washington
Gaevskaja, A.V. and V.K. Machkevsky. – 1995. Impact of ManMade Coastal Structures on Formation and Function of Parasite
Systems. ECOSET-95 Proceedings, I. Japan: 531-536.
Ginetsynskaja, T.A. and A.A. Dobrovolsky. – 1978. Particular
Parasitology: Parasitic Protozoans and Flatworms, 1. Vshaja
Shkola, Moscow.
Kamara, A.B. – 1982. Preliminary studies on culturing mangrove
oysters Crassostrea tulipa in Sierra Leone. Aquaculture, 27:
285-295.
Ko, R.S. – 1975. Echinocephalus sinensis n. sp. (Nematoda:
Gnathostomatidae) from the ray (Aetobatus flagellum) in Hon
Kong, Southern China. Can. J. Zool., 53: 490-500.
Ko, R.S. – 1976. Experimental infection of mammals with larval
Echinocephalus sinensis (Nematoda: Gnathostomatidae) from
oysters (Crassostrea gigas). Can. J. Zool., 54: 597-609.
Ko, R.S. – 1977. Effects of temperature acclimation of infection of
Echinocephalus sinensis (Nematoda: Gnathostomatidae) from
oysters to kittens. Can. J. Zool., 55: 1129-1132.
Ko, R.S., Morton, B. and Wong, P.S. – 1975. Prevalence and
histopathology of Echinocephalus sinensis (Nematoda:
Gnathostomatidae) in natural and experimental hosts. Can. J.
Zool., 53: 550-559.
Machkevsky, V.K. – 1992. A new crab species, Pinnotheres larissae sp.n. (Decapoda Brachiura Pinnotheridae) from the mangrove oyster Crassostrea tulipa (Bivalvia Ostreidae) of West
Africa. Russian Journal of Arthropoda Research, I(3): 83-88.
Morozova, A.L., K.D. Leun Tack, V.I. Knodolov, V.V. Trusevich,
S. Kamara, V.K. Machkevsky, F.H. Ibrahimov and P.D.
Lomakin. – 1991. L'Ostréiculture en milieux de Mangroves
(Etude de cas en Guinée et au Senegal). Série Documentaire the
COMARAF Project, N7.
Najdenova, N.N. – 1988. Infection of the Fishes of the Shellf of
Guinea. In: Eremeev, V.N. (ed.), Tropical Atlantic (Region of
Guinea), pp. 325-337. Kiev. Naukova Dumka.
Skrjabin, K.I. and E.J. Bashkirova. – 1956. Trematodes of Animals
and People (Fam. Echinostomatidae), pp. 51-917. V. XII. M.,
Izdatelstvo Akademii Nauk USSR.
Szuks, H. – 1981. Zu Vorkommen von Lobatostoma ringens (Aspidogastridae, Trematoda) vor der Kuste Nordwestafrikas. Wiss.
Zeitschr. Padagog. Hochschulte “Lisselotte Herrmann” Gustrove Math.-Naturwiss. Fak.: 25-29.
ENDOSYMBIONTS OF MANGROVE OYSTER 107