MULTI-INFECTION PATTERN IN THE EXPLOITED MANILA CLAM (Ruditapes philippinarum) OF 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: t in th largest producer behind China, Korea, Japan, Italy, USA and Spain → Manila clam production Fishing and Farming of different species of clam: - World = t - Europe = 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 The second most commercially important mollusk - 70 fishing licences Arcachon bay 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 ATLANTICOCEANATLANTICOCEAN 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 Metacercaria encysted 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 Cysts abundance

Results and discussion A/ Digenean Trematodes → Experimental infestation by cercariae at 22 °C - 15 boxes with 1 cockle (C. edule) - 15 boxes with 1 Manila clam 40 cercariae of H. elongata per box Cysts abundance → 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 Cysts abundance

Results and discussion 1/ Temporal survey  Dominance of stage 1  Temporal and spatial homogeneity (p>0.05) B/ BRD induced by Vibrio tapetis BRD prevalence Infection stages Lanton  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 Infection stages 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 Infecting stage spreading stage Zoosporangium Zoospores CLAM SEA WATER Dead animal Cycle: Auzoux-Bordenaze and al., 1995 Cycle of P. olseni Results and discussion C/ 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 P. Olseni prevalence  High prevalence: between 80 and 100 %  No significant difference of P. olseni prevalence between months and sites (p>0.05) Infection intensity

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 index Biomass Tidal level Leyre proximity SalinitySPMP P. olseni prevalence P. olseni intensity  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 P. olseni intensity BRD prevalence BRD infection stages → 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

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