multi-infection pattern in the exploited manila clam (ruditapes philippinarum) of arcachon bay...

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


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


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.)


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


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



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



oct-06

Andernos

Gujan

Lanton

Ile

Infe

ctio

n i

nte

ns

ity


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:


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

And, if you have any questions,

please speak slowly…

multi-infection pattern in the exploited manila clam (ruditapes philippinarum) of arcachon bay...

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