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MULTI-INFECTION PATTERN IN MULTI-INFECTION PATTERN IN THE EXPLOITED MANILA CLAM THE EXPLOITED MANILA CLAM
((Ruditapes philippinarumRuditapes philippinarum) OF ) OF ARCACHON BAY (France)ARCACHON BAY (France)
Dang C.1, Saez S.1, de Montaudouin X.1, Caill-Milly N.2, Gonzales P. 1, Huchin F. 1
1 Arcachon Marine Station, UMR 5805, University of Bordeaux 1-CNRS, France
2 Ifremer, Aquitaine Resources Laboratory, Bidart, France
R. philippinarum: - 3000 t in 2005- 7th largest producer behind China, Korea, Japan, Italy, USA and Spain
→ Manila clam production
Fishing and Farming of different species of clam:
- World = 3 442 154 t
- Europe = 167 920 t (Italy: 87 kt, Spain: 23 kt, England: 20 kt, Holland: 19 kt, France: 9 kt)
Worldwide:
In France:
In Arcachon Bay:
- The first place in France with 450 t in 2005
- The second most commercially important mollusk
- 70 fishing licences
Arcachon bay
Introduction
Introduction
Monitoring of three pathologies:
- At the temporal scale by a monthly survey in 4 sites
- At the spatial scale by a unique sampling campaign performed in May 2006 and concerning 35 stations scattered in the lagoon
- Pathologies occurrence were correlated to environmental conditions
Impact of pathologies on clam physiology: condition and calcification indices
→ Objectives of this work
→ The studied site
• Semi-sheltered lagoon characterized by a communication with Atlantic Ocean, tidal rhythms and fresh-water input (streams, ground water….)
• 70% of tidal flats colonized by Manila clam
• The largest sea-grass beds in Europe
Material and Methods
N
ATLANTIC
OCEAN Leyre (river)
Manila clam areas
→ Methods
Material and methods
Map of Arcachon bay showing the sampling stations
• 4 sites have been studied each month since November 2005 ( )
• 35 stations have been sampled in May 2006 ( )
Environmental parameters assessed:
- tidal level- oceanic, river and first coast proximities - Salinity- Temperature- Suspended Particulate Matter (SPM)…
Life cycle of Himasthla elongata
A/ Digenean Trematodes Results and discussion
Head of Himasthla elongata
Adult
Miracidium larva
Redies
Cercaria
Metacercariaencysted
Parasite stage
Free stage
predation
Marine bird
L. littorea
second host First host
Final host
R.philippinarum
Results and discussion
• Manila clams are hardly infected by Digenean trematodes in the four sites
• Abundance of trematodes is similar according to time and sites (p > 0.05)
Two hypotheses:
1/ no cercariae in the field ?
2/ clam resistance ?
A/ Digenean Trematodes
0
1
2
3
4
5
nov-05dec-05janu-06feb-06
march-06
apr-06may-06june-06july-06augu-06sept-06
Gujan
Andernos
Ile
Lanton
Cy
sts
ab
un
da
nc
e
Results and discussionA/ Digenean Trematodes
→ Experimental infestation by cercariae at 22 °C
- 15 boxes with 1 cockle (C. edule)
- 15 boxes with 1 Manila clam40 cercariae of H. elongata per box
0
10
20
30
cockle clamCy
sts
a
bu
nd
an
ce
→ Clams resist to cercarial infection unlike cockles
Cockles are more infected than Manila clams
→ Cercariae are potentially present in the field; potential infection exists
→ Comparison between Manila clam and cockle (Cerastoderma edule) in natural environment
0
10
20
30
40
cockle clam
Cy
sts
a
bu
nd
an
ce
Results and discussion
1/ Temporal survey
Dominance of stage 1
Temporal and spatial homogeneity (p>0.05)
B/ BRD induced by Vibrio tapetis
0102030405060708090
100
nov-05dec-05janu-06febr-06march-06
april-06may-06june-06july-06augu-06sept-06
Andernos
Gujan
Lonton
Ile
BR
D p
rev
ale
nc
e
0%
20%
40%
60%
80%
100%
dec-05janu-06febr-06march-06
april-06may-06june-06july-06augu-06sept-06
st. 7
st.6
st. 5
st.4
st.3
st.2
st. 1
st. 0
Infe
cti
on
sta
ge
sLanton
Low BRD prevalence
Temporal and spatial homogeneity (p>0.05)
V. tapetis (photo: Paillard, C.)
Results and discussion
2/ Spatial survey
Low prevalence (mean = 12 %)
Dominance of stage 1
B/ BRD induced by V. tapetis
0
20
40
60
80
100
A49A20A68Ar
B70B94B47C72C60C59D1 D2 D3 E9E13E16G10S1-6S1-32S1-8S4-31S4-21S4-39S6-14S6-1S6-13Z1-12Z1-23Z1-21Z1-24Z1-11
Z2-6Z2-19Z2-16Gu-1
L-1 A1 î1
% st 7
% st 6
% st 5
% st 4
% st 3
% st 2
% st 1
% st 0
Infe
ctio
n s
tag
es
Stage 7
Stage 1
Results and discussion
Multiple regressions have been realized between BRD prevalence, BRD stages and environmental factors
→ but no correlation has been found.
Gradation of stage infection
-
+
Map representing the BRD infection
→ Manila clams are poorly infected by V. tapetis
B/ BRD induced by V. tapetis
Prezoosporangium
Growing stage
Proliferating stage
Trophozoïtes
Infectingstage
spreadingstage
Zoosporangium
Zoospores
CLAM
SEA WATER
Dead animal
Cycle: Auzoux-Bordenaze and al., 1995
Cycle of P. olseni
Results and discussionC/ Perkinsus olseni
1/ Temporal survey
No significant difference of P. olseni intensity between months and sites (p>0.05)
C/ Perkinsus olseni Results and discussion
0
20
40
60
80
100
120
nov-05dec-05janu-06febr-06march-06
april-06may-06june-06july-06augu-06sept-06
Andernos
Gujan
Lanton
Ile
P.
Ols
eni
pre
vale
nce High prevalence:
between 80 and 100 %
No significant difference of P. olseni prevalence between months and sites (p>0.05)
0
50000
100000
150000
200000
250000
300000
nov-05dec-05janu-06febr-06march-06
april-06may-06june-06july-06augu-06sept-06
oct-06
Andernos
Gujan
Lanton
Ile
Infe
ctio
n i
nte
ns
ity
Results and discussion
2/ Spatial survey
High prevalence of P. olseni around the bay: between 70 and 100%
No P. olseni in oceanic area
Distribution of P. olseni intensity follows environmental parameters such as the salinity gradient
C/ Perkinsus olseni
Condition index
Calcification
indexBiomass
Tidal
level
Leyre
proximitySalinity SPM P
P. olseni
prevalence-0.49 0.031
P. olseni
intensity-0.57 -0.49 1.19 1.91 2.12 0.002
Results of multiple regression:
Salinity gradient
+
-
Low intensities
5 km
High intensities
Medium intensities
Map representing the P. olseni intensities
D/ Interaction between BRD and P. olseni
Comparison of P. olseni prevalence, P. olseni intensities, BRD prevalence, BRD stage each other:
Results and discussion
P. olseni
prevalence
P. olseni intensity
BRD prevalence
BRD infection stages
P. olseni prevalence 0.28 0.07 0.12
P. olseni intensity 0.28 0.09 0.01
BRD prevalence 0.07 0.09 0.83
BRD infection stages 0.12 0.01 0.83
→ No multi-infection correlation
(r coefficient)
Conclusion
Digenean trematodes and V. tapetis are hardly present in Manila clams and have no effect on condition index
The most important parasite is P. olseni but it has no repercussion on condition index
→ None of these three pathologies should be involved in high mortalities
Observation of a disease in mortalities areas which induces a hardening of the posterior muscle
It disturbs the opening and closing of valves: clam can no longer bury
→ This study is preliminary
Thank you for your attention
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