Spatio-temporal variations in biological performances and summer mortality of the Pacific oyster Crassostrea gigas in Normandy (France)

Abstract

Mortality and biological performances of halfgrown Crassostrea gigas were studied from spring 2000 to autumn 2001 at six instrumented stations located in two areas (Gefosse and Grandcamp) of the Bay of Veys (Normandy). Shell and meat growth, condition indexes and a macroscopic maturity index were determined on oysters deployed at the six stations in order to assess spatial variability in the influence of environmental conditions. In addition, histological and biochemical analyses were performed in order to determine the sex and establish the reproductive cycle (at all six sites) and the biochemical composition (at four stations). The data set including monthly mean temperatures and data provided by examination of 2,837 oysters were analysed by Principal Component Analysis and a Hierarchical Ascending Clustering which resulted in the formation of four clusters. The highest station on the shoreline belonged to a cluster characterized notably by low total weight due to a short immersion/feeding period, whereas all other stations belonged to another single cluster. Nevertheless, various biological differences were found between these stations, e.g. the reproductive cycle was generally synchronized throughout the bay but some differences relative to spawning occurrence were observed. In 2000, oyster mortality was higher at Gefosse than at Grandcamp, the latter being a more marine area.In 2001, oyster mortalities were significantly higher and all stations were strongly affected. In the Bay of Veys, oyster biological performances and mortality thus showed spatio-temporal variations which were worthy to be discussed.

Biochemical and elemental composition of the offshore-cultivated oysters Ostrea edulis and Crassostrea gigas

“…Energy utilization in C. gigas coincided with reduced shell growth and a decrease in DM (Pogoda et al, 2011). This may be explained by reproductive effort, as during summer C. gigas >40 mm starts to invest energy in gonad maturation (Costil et al, 2005;Royer et al, 2008). The simultaneous glycogen decrease and lipid increase may indicate the conversion of carbohydrates into lipids during ontogenesis (De la Parra et al, 2005;Robinson, 1992;Whyte et al, 1990), as lipid contents of oyster eggs are directly related to survival rates of the lecithotrophic embryonic stages and veliger larvae (Gallager and Mann, 1986).…”

“…Several studies were carried out on seasonal changes of the biochemical composition of oysters (Abad et al, 1995;Costil et al, 2005;Dridi et al, 2007;Li et al, 2009;Linehan et al, 1999;Robert et al, 1993;Ruíz et al, 1992;Soletchnik et al, 2006). However, no information is available about the biological performance and fitness of oysters grown under offshore farming conditions.…”

Growth and economic performance of diploid and triploid Pacific oysters Crassostrea gigas cultivated in three lagoons of the Gulf of California

“…On other hand, the higher mortality values for all groups were observed in the same time period. It is well documented that summer mortality of Pacific oyster are associated to water temperature exceeding 20°C (Costil et al, 2005;Gagnaire et al, 2006) that in many cases, promote favorable conditions for pathogens as well (Enríquez-Espinoza et al, 2010). Therefore, it is possible assume that BW and survival of diploid and triploid oyster were strongly affected for the high water temperature during the first five cultivation months (summer).…”

Transcriptional expression levels of cell stress marker genes in the Pacific oyster Crassostrea gigas exposed to acute thermal stress

“…Moreover, it should be kept in mind that temperature is not the only parameter changing with the seasons and suspected to be responsible for stress in oysters. Other parameters include environmental factors such as trophic conditions, oxygen and nature of sediment (Delaporte et al 2003;Soletchnik et al 2005) as well as physiological and genetic factors such as reproduction, oxidative stress and parasitism (Le Roux et al 2002;Huvet et al 2004;Costil et al 2005). …”