Latitudinal drivers of oyster mortality: deciphering host, pathogen and environmental risk factors

Abstract

Diseases pose an ongoing threat to aquaculture, fisheries and conservation of marine species, and determination of risk factors of disease is crucial for management. our objective was to decipher the effects of host, pathogen and environmental factors on disease-induced mortality of Pacific oysters (Crassostrea gigas) across a latitudinal gradient. We deployed young and adult oysters at 13 sites in france and we monitored survival, pathogens and environmental parameters. the young oysters came from either the wild collection or the hatchery while the adults were from the wild only. We then used Cox regression models to investigate the effect of latitude, site, environmental factors and origin on mortality risk and to extrapolate this mortality risk to the distribution limits of the species in europe. We found that seawater temperature, food level, sea level atmospheric pressure, rainfall and wind speed were associated with mortality risk. Their effect on hatchery oysters was generally higher than on wild animals, probably reflecting that hatchery oysters were free of Ostreid herpesvirus 1 (OsHV-1) whereas those from the wild were asymptomatic carriers. the risk factors involved in young and adult oyster mortalities were different, reflecting distinct diseases. Mortality risk increases from 0 to 90% with decreasing latitude for young hatchery oysters, but not for young wild oysters or adults. Mortality risk was higher in wild oysters than in hatchery ones at latitude > 47.6°N while this was the opposite at lower latitude. Therefore, latitudinal gradient alters disease-induced mortality risk but interacts with the initial health status of the host and the pathogen involved. practically, we suggest that mortality can be mitigated by using hatchery oysters in north and wild collected oysters in the south.

Case study of vertical transmission of ostreid herpesvirus‐1 in Pacific oysters and biosecurity management based on epidemiological data from French, New Zealand and Australian hatchery‐propagated seed

“…We assume that many more of the progenitors would have been latently infected based on our findings and from previous studies (Degremont & Benabdelmouna, 2014;Fleury et al, 2020;Jouaux et al, 2013;Paul-Pont et al, 2014). The lack of vertical transmission in all the batches of C. gigas progenies reported here most likely reflects an absence of key triggers for viral reactivation to occur in asymptomatic broodstock held in hatcheries, for example temperature and/or other environmental stressors.…”

“…Following epidemics driven by high water temperature in summer months, the putative latent infection persists in a proportion of the oyster population, with virus reactivation occurring weeks to months later (Dégremont et al, 2013; Fleury et al, 2020; Green et al, 2014; Jouaux et al, 2013; Segarra et al, 2014). Although temperature increase is well known as a key trigger of this disease, the mechanism that reactivates the infectious lytic cycle and also confirmation of latency is yet to be fully documented (Jouaux et al, 2013; Nguyen et al, 2019).…”

The Pacific Oyster Mortality Syndrome, a Polymicrobial and Multifactorial Disease: State of Knowledge and Future Directions

“…In different invertebrate–pathogen interactions, temperature has been found to affect the outcome of the interaction by influencing host and/or pathogen physiology ( 59 – 63 ). A permissive temperature range for POMS has been clearly identified, specifically, 16°C to 24°C ( 5 , 6 , 64 ). The same trend was observed in mesocosm experiments in which recipient oysters were confronted to disease donors at different temperature [ Figure 2A , ( 16 )].…”

“…For decades, C. gigas has suffered from mortality due to disease ( 4 ), but the severity of these outbreaks has increased dramatically since 2008. These outbreaks affect the juvenile stages of the oyster, killing more than 35% of the cultivated and natural oysters in France every year ( 5 , 6 ). The corresponding syndrome, referred to as Pacific oyster mortality syndrome (POMS) ( 7 ), has become panzootic; it is observed in all the coastal regions of Franc, and in numerous other countries worldwide ( 8 ).…”

Transcriptomics Analysis and Re-sequencing Reveal the Mechanism Underlying the Thermotolerance of an Artificial Selection Population of the Pacific Oyster

“…Previous studies have suggested that environmental parameters, the physiological and genetic status of oysters, and the synergistic effects of pathogenic microorganisms may contribute to summer mortality (Tomaru et al, 2001; de Lorgeril et al, 2011;Genard et al, 2012). Seawater temperature, the amount of food, sea level atmospheric pressure, rainfall, and wind speed have all been associated with mortality risk (Fleury et al, 2020). Among all of the abiotic and biological factors that cause oyster mass mortality in summer, temperature rise is considered the most important (Le Roux et al, 2002;Gay et al, 2004;Meng et al, 2014).…”