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Diseases of Aquatic Organisms

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DAO 156:7-13 (2023)  -  DOI:

Decline of Marteilia cochillia in Ría de Arousa may be due to increased resistance in host Cerastoderma edule

David Iglesias1, Asunción Cao1, María J. Carballal1, Antonio Villalba1,2,3,*

1Centro de Investigacións Mariñas (CIMA), Consellería do Mar, Xunta de Galicia, 36620 Vilanova de Arousa, Spain
2Departamento de Ciencias de la Vida, Universidad de Alcalá, 28871 Alcalá de Henares, Spain
3Research Centre for Experimental Marine Biology and Biotechnology (PIE), University of the Basque Country (UPV/EHU), 48620 Plentzia, Spain
*Corresponding author:

ABSTRACT: A huge, unprecedented mortality of cockle Cerastoderma edule caused by the protist Marteilia cochillia, which had never before been detected in Galicia (NW Spain), brought on a cockle fishery collapse in the Ría de Arousa (Galicia) in 2012. Since then, the disease dynamic pattern in the shellfish bed of Lombos do Ulla (at the inner area of that ria) involved an overwhelming annual wave of infections and subsequent cockle mass mortality that caused the near extinction of every cohort recruited to that bed. However, a pattern shift was detected among wild cohorts recruiting since 2016, with progressive declines of marteiliosis prevalence and increments in cockle survival. This suggested 2 non-exclusive hypotheses: increasing marteiliosis resistance through natural selection, and reduced abundance and/or virulence of the parasite. A field experiment was performed to assess these hypotheses by comparing marteiliosis prevalence and severity, as well as mortality, in cockles that naturally recruited to this bed in 2017 and 2018 with those of naïve cockles collected from a marteiliosis-free area and transplanted into Lombos do Ulla in 2017 and 2018. Marteiliosis prevalence and cumulative cockle mortality quickly reached very high values among the transplanted cockles, demonstrating that the parasite remained present and virulent in the area. Conversely, marteiliosis prevalence and cockle mortality were much lower in the cockles that recruited to Lombos do Ulla, suggesting increased resistance that may have been driven by natural selection. The young age at which cockles start reproduction and the very high mortality caused by marteiliosis may have enhanced natural selection.

KEY WORDS: Cerastoderma edule · Bivalve mollusc · Protistan parasite · Disease dynamics · Resistance · Natural selection

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Cite this article as: Iglesias D, Cao A, Carballal MJ, Villalba A (2023) Decline of Marteilia cochillia in Ría de Arousa may be due to increased resistance in host Cerastoderma edule. Dis Aquat Org 156:7-13.

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