Physiological responses of Manila clams Venerupis (=Ruditapes) philippinarum with varying parasite Perkinsus olseni burden to toxic algal Alexandrium ostenfeldii exposure

Abstract

Manila clam stock from Arcachon Bay, France, is declining, as is commercial harvest. To understand the role of environmental biotic interactions in this decrease, effects of a toxic dinoflagellate, Alexandrium ostenfeldii, which blooms regularly in Arcachon bay, and the interaction with perkinsosis on clam physiology were investigated. Manila clams from Arcachon Bay, with variable natural levels of perkinsosis, were exposed for seven days to a mix of the nutritious microalga T-Iso and the toxic dinoflagellate A. ostenfeldii, a producer of spirolides, followed by seven days of depuration fed only T-Iso. Following sacrifice and quantification of protozoan parasite Perkinsus olseni burden, clams were divided into two groups according to intensity of the infection ("Light-Moderate" and "Moderate-Heavy"). Hemocyte and plasma responses, digestive enzyme activities, antioxidant enzyme activities in gills, and histopathological responses were analyzed. Reactive oxygen species (ROS) production in hemocytes and catalase (CAT) activity in gills increased with P. olseni intensity of infection in control clams fed T-Iso, but did not vary among A. ostenfeldii-exposed clams. Exposure to A. ostenfeldii caused tissue alterations associated with an inflammatory response and modifications in hemocyte morphology. In the gills, superoxide dismutase (SOD) activity decreased, and an increase in brown cell occurrence was seen, suggesting oxidative stress. Observations of hemocytes and brown cells in tissues during exposure and depuration suggest involvement of both cell types in detoxication processes. Results suggest that exposure to A. ostenfeldii disrupted the pro-/anti-oxidant response of clams to heavy P. olseni intensity. In addition, depressed mitochondrial membrane potential (MMP) in hemocytes of clams exposed to A. ostenfeldii suggests that mitochondrial functions are regulated to maintain homeostasis of digestive enzyme activity and condition index.

Interaction between toxic dinoflagellate Alexandrium catenella exposure and disease associated with herpesvirus OsHV-1 μVar in Pacific oyster spat Crassostrea gigas

“…Although immune defense against herpesvirus is not well documented, hemocyte-mediated responses appear to be involved, as shown by hemocyte infiltrations (Jenkins et al, 2013) and differentially expressed genes related to hemocyte functions in virus-infected oysters (Green et al, 2014;Jouaux et al, 2013;Renault et al, 2011). Previous studies showed an inflammatory response in bivalves exposed to Alexandrium sp., which increased circulating hemocyte concentration, as well as hemocyte infiltration and diapedesis, particularly in the digestive gland but also in the gills and the mantle (Galimany et al, 2008a;Haberkorn et al, 2010aHaberkorn et al, , 2010bLassudrie et al, 2014). More numerous hemocytes in these organs that are also targeted by OsHV-1 (Corbeil et al, 2015;Schikorski et al, 2011a) could result in a faster, more efficient defense and accelerate elimination of herpesvirus, possibly through release of humoral factors.…”

“…In fact, exposure to Alexandrium spp. modulated antioxidant mechanisms (enzyme activity or gene expression) in clams and oysters (Estrada et al, 2007;Lassudrie et al, 2014;Romero-Geraldo and Herná ndez-Saavedra, 2012), and increased observations of ceroid bodies (containing oxidized molecules) in tissues (Galimany et al, 2008b;Lassudrie et al, 2014). Oxidation of the viral envelope could decrease virus viability, but also may alter entry mechanisms into the host cells, as well as interfering with viral replication (Lorizate and Krä usslich, 2011).…”

“…Alterations of physiological processes and tissue integrity have been reported in bivalves after a few hours to a few (4-9) days of exposure to Alexandrium sp. cells (10 2 -10 3 cells mL À1 ) (Cucci et al, 1985;Shumway, 1988a, 1988b;Galimany et al, 2008a;Haberkorn et al, 2010b;Landsberg, 2002;Lassudrie et al, 2014;Medhioub et al, 2012;Shumway, 1990). Hemocytes, which are involved in many functions including immunity, also are affected by Alexandrium sp.…”

Physiological and pathological changes in the eastern oyster Crassostrea virginica infested with the trematode Bucephalus sp. and exposed to the toxic dinoflagellate Alexandrium fundyense

“…A positive effect of A. minutum exposure (depending upon the season and the oyster ploidy) or of toxin accumulation, however, was reported upon THC in C. gigas (Haberkorn et al, 2010a;Hégaret et al, 2007), possibly stimulating the immune system. Modifications of cellular proand anti-oxidant mechanisms, which may participate in the immune response and are involved in cellular protection, also have been reported (Fabioux et al, in preparation;Lassudrie et al, 2014). Whether or not these effects upon immune-related variables are direct consequences of Alexandrium sp.…”

“…exposure could not be assessed, because Alexandrium spp. also affect general physiological processes (Cucci et al, 1985;Shumway, 1988a, 1988b;Landsberg, 2002;Shumway, 1990) and tissue integrity (Galimany et al, 2008;Haberkorn et al, 2010b;Lassudrie et al, 2014;Medhioub et al, 2012), that could indirectly affect hemocytes.…”