Spatial and Temporal Dynamics of Mass Mortalities in Oysters Is Influenced by Energetic Reserves and Food Quality

Abstract

Although spatial studies of diseases on land have a long history, far fewer have been made on aquatic diseases. Here, we present the first large-scale, high-resolution spatial and temporal representation of a mass mortality phenomenon cause by the Ostreid herpesvirus (OsHV-1) that has affected oysters (Crassostrea gigas) every year since 2008, in relation to their energetic reserves and the quality of their food. Disease mortality was investigated in healthy oysters deployed at 106 locations in the Thau Mediterranean lagoon before the start of the epizootic in spring 2011. We found that disease mortality of oysters showed strong spatial dependence clearly reflecting the epizootic process of local transmission. Disease initiated inside oyster farms spread rapidly beyond these areas. Local differences in energetic condition of oysters, partly driven by variation in food quality, played a significant role in the spatial and temporal dynamics of disease mortality. In particular, the relative contribution of diatoms to the diet of oysters was positively correlated with their energetic reserves, which in turn decreased the risk of disease mortality.

Do Temporal and Spatial Parameters or Lifestyle of the Pacific Oyster Crasssostrea gigas Affect Pollutant Bioaccumulation, Offspring Development, and Tolerance to Pollutants?

“…Since 1998, several years have been particularly unfavorable for oyster larval recruitment and several episodes of high mortality of oyster spat have been recorded in the Arcachon Bay. In many countries worldwide, the occurrence of significant mass mortalities in both adult and juvenile C. gigas populations has been reported, generally during the summer months (Mori, 1979;Perdue et al, 1981;Watermann et al, 2008;Cotter et al, 2010;Pernet et al, 2011). Although the mass mortality phenomenon encountered in recent years is often associated with infectious agents, it is also often related to environmental changes and highlights the delicate balance that governs an ecosystem.…”

Oyster mortality

“…For example, mortality of oysters maintained in Thau lagoon but outside the farming area coincided with relatively strong currents coming from the farming area where mortality was occurring and OsHV-1 DNA was detected. Similarly, mortality of oysters induced by OsHV-1 showed strong spatial dependence clearly reflecting the epizootic process of local transmission (Pernet et al, 2014b). OsHV-1-induced mortality originates inside oyster farms and spreads rapidly beyond these areas, likely reflecting water movements (Paul-Pont et al, 2014;Pernet et al, 2014b).…”

“…The viral load can gradually decrease indicating the ability of oysters to suppress virus replication. When seawater temperature is higher than 16 °C, mortalities associated with OsHV-1 continue for 10 to 40 days (Peeler et al, 2012;Paul-Pont et al, 2013b;Pernet et al, 2014b;Renault et al, 2014a;Batista et al, 2015). …”

“…However, a high level of viral DNA was not systematically associated with mortality that depended on sites (Pernet et al, 2014b), husbandry practices (Pernet et al, 2012) and genetic background of oysters (Dégremont, 2011).…”

“…Alternatively, oysters with high energy reserves are probably less affected by pathogen infections than those with low levels (Pernet et al, 2012), as reported for several vertebrate species. It was recently reported that local differences in energetic condition of oysters, partly driven by variation in food quality, played a significant role in the spatial and temporal dynamics of disease mortality (Pernet et al, 2014b) . In particular, the relative contribution of diatoms to the diet of oysters was positively correlated with their energetic reserves, which in turn decreased the risk of disease mortality.…”