DAO 61:103-111 (2004)  -  doi:10.3354/dao061103

Infection dynamics of Marteilia refringens in flat oyster Ostrea edulis and copepod Paracartia grani in a claire pond of Marennes-Oléron Bay

Corinne Audemard1,4,*, Marie-Céline Sajus2, Antoine Barnaud1, Benoit Sautour2, Pierre-Guy Sauriau3, Frank J. C. Berthe1

1Laboratoire Génétique et Pathologie, IFREMER, BP 133, 17390 La Tremblade, France
2Laboratoire d¹Océanographie Biologique, UMR 5805 Université Bordeaux I, CNRS, 2 rue du Professeur Jolyet, 33120 Arcachon, France
3 Centre de Recherche sur les Ecosystèmes Marins et Aquacoles de l¹Houmeau (CREMA, UMR 10 CNRS-IFREMER), BP 5, 17137 L¹Houmeau, France
4Present address: Virginia Institute of Marine Sciences, PO Box 1346, College of William & Mary, Gloucester Point, Virginia 23062, USA

ABSTRACT: The protozoan parasite Marteilia refringens has been partly responsible for the severe decrease in the production of the European flat oyster Ostrea edulis Linnaeus in France since the 1970s. The calanoid copepod Paracartia grani Sars was recently found to be a host for M. refringens in French shallow-water oyster ponds (Œclaires¹). This study reconsidered M. refringens transmission dynamics in the light of this finding, taking into account not only oyster infection dynamics and environmental factors but also data concerning the copepod host. P. grani population dynamics in the claire under study revealed that this species is the dominant planktonic copepod in this confined ecosystem. During winter, M. refringens overwintered in O. edulis, with P. grani existing only as resting eggs in the sediment. The increase in temperature in spring controlled and synchronized both the release of M. refringens sporangia in the oyster feces, and the hatching of the benthic resting eggs of the copepod. Infection of oysters by M. refringens was limited to June, July and August, coinciding with (1) the highest temperature recorded in the claire, and (2) the highest abundance of P. grani. PCR detection of M. refringens in P. grani during the summer period was linked to the release of parasite sporangia by the oyster. Our results are supported by previous results on the effective transmission of this parasite from the oyster to the copepod.

KEY WORDS: Marteilia refringens · Ostrea edulis · Paracartia grani · Infection dynamics · Claire pond

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