Abstract
AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 11:493-506 (2019) - DOI: https://doi.org/10.3354/aei00327 Connectivities with shellfish farms and channel rivers are associated with mortality risk in oysters Aline Gangnery1,*,**, Julien Normand1,**, Cyrielle Duval1, Philippe Cugier2, Karine Grangeré3, Bruno Petton4, Sébastien Petton4, Francis Orvain3, Fabrice Pernet5 1Ifremer, Laboratoire Environnement Ressources de Normandie, Avenue du Général de Gaulle, 14 520 Port en Bessin, France 2Ifremer, Laboratoire d’Ecologie Benthique Côtière, Technopole Brest-Iroise, 29 280 Plouzané, France 3Université de Caen Basse-Normandie, UMR BOREA, Esplanade de la Paix, BP 5186, 14 032 Caen cedex, France 4Ifremer, UMR 6539 LEMAR, 11 presqu’île du vivier, 29 840 Argenton en Landunvez, France 5Ifremer, UMR 6539 LEMAR, Technopole Brest-Iroise, 29 280 Plouzané, France *Corresponding author: aline.gangnery@ifremer.fr**These authors contributed equally to this work ABSTRACT: Oyster diseases have major consequences on fisheries and aquaculture. In France, young Pacific oysters Crassostrea gigas are severely hit by the ostreid herpesvirus, whereas adults suffer mortalities presumably caused by pathogenic bacteria. Here we investigated the origin and spread of mortalities that affect both young and adult oysters, and we identified and compared their risk factors. Mortality was monitored in 2 age classes of oysters deployed in early spring at 39 sites spread over a 37 km2 surface area inside and outside of shellfish farms. Environmental data obtained from numerical modelling were used to investigate risk factors. Mortality of young oysters associated with ostreid herpesvirus occurred in the oyster farming area. Hydrodynamic connectivity with oyster farms was associated with higher mortality risk, whereas chlorophyll a concentration was associated with a lower risk. Adult oysters experienced 2 mortality events that were associated with different risk factors. The first event, which occurred after deployment and was probably caused by endogenous pathogens, was mainly associated with connectivity to channel rivers and salinity. The second mortality event observed at the end of the summer was mainly associated with connectivity to oyster farms, suggesting pathogen transmission. The risk factors involved in young and adult oyster mortalities were partly different, reflecting distinct origins. Connectivity with oyster farms is a mortality risk factor for both young and adult oysters; thus, disease management strategies that focus on oyster farming areas will impact overall disease risk. KEY WORDS: Aquaculture · Bivalve · Disease · Epidemiology and health · Ecological modelling · Hydrodynamic connectivity Full text in pdf format Supplementary material PreviousNextCite this article as: Gangnery A, Normand J, Duval C, Cugier P and others (2019) Connectivities with shellfish farms and channel rivers are associated with mortality risk in oysters. Aquacult Environ Interact 11:493-506. https://doi.org/10.3354/aei00327 Export citation Mail this link - Contents Mailing Lists - RSS Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 11. Online publication date: September 19, 2019 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2019 Inter-Research.
Highlights
Mortality outbreaks in Pacific oyster Crassostrea gigas associated with diseases of complex aetiology have increased during the last 10 yr worldwide (Barbosa Solomieu et al 2015, EFSA AHAW Panel 2015)
Association between environmental variables reflect observations (Fig. 3a), as (1) a mortality outand mortality risk break occurred in the farming area of Grandcamp, (2) cumulative mortality reached 30% at many sites, Connectivity to the Grandcamp farming area was (3) no mortality occurred in the central part of the strongly associated with a higher risk of mortality in bay, and (4) low mortality was observed at 1 site in young oysters
This suggests that a high oyster density provides suitable conditions for an OsHV-1 outbreak, as previously reported in a Mediterranean lagoon (Pernet et al 2014a,b) and along an inshore−offshore gradient in Brittany (Pernet et al 2018). This is consistent with the general principles of population dynamics of infectious diseases (Anderson & Multiple covariates Connectivity Grandcamp farming area (May) 1979) that apply to marine organisms (McCallum et al 2004, Krkošek 2010)
Summary
Mortality outbreaks in Pacific oyster Crassostrea gigas associated with diseases of complex aetiology have increased during the last 10 yr worldwide (Barbosa Solomieu et al 2015, EFSA AHAW Panel 2015). In temperate estuarine ecosystems, mortality of adult oysters was associated with the temporal increase in seawater temperature during the warm season, freshwater outflow from rivers and subsequent drop in salinity, and excessive increase in nutrient and phytoplankton concentrations, which induce metabolic disorders associated with reproductive effort and stress (Delaporte et al 2006, Royer et al 2007, Soletchnik et al 2007, Bushek et al 2012, Go et al 2017) This agrees with the fact that mortality events recorded along the Atlantic coast of France between 1986 and 2015 usually occur several months after winters dominated by the occurrence of positive North Atlantic oscillation (NAO+) atmospheric regimes of circulation (Thomas et al 2018). High-frequency data of seawater temperature, salinity, phytoplankton concentration and hydrodynamic connectivity to oyster farms and to the river channels were obtained from a 3D hydrodynamic model coupled with a biogeochemical model and further used to investigate mortality risk factors
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