Experimental exposure of the blue mussel (Mytilus edulis, L.) to the toxic dinoflagellate Alexandrium fundyense: Histopathology, immune responses, and recovery

Abstract

The harmful dinoflagellate Prorocentrum minimum has different effects upon various species of grazing bivalves, and these effects also vary with life-history stage.Possible effects of this dinoflagellate upon mussels have not been reported; therefore, experiments exposing adult blue mussels, Mytilus edulis, to P. minimum were conducted. Mussels were exposed to cultures of toxic P. minimum or benign Rhodomonas sp. in glass aquaria. After a short period of acclimation, samples were collected on day 0 (before the exposure) and after 3, 6, and 9 days of continuousexposure experiment. Hemolymph was extracted for flow-cytometric analyses of hemocyte, immune-response functions, and soft tissues were excised for histopathology.Mussels responded to P. minimum exposure with diapedesis of hemocytes into the intestine, presumably to isolate P. minimum cells within the gut, thereby minimizing damage to other tissues. This immune response appeared to have been sustained throughout the 9-day exposure period, as circulating hemocytes retained hematological and functional properties. Bacteria proliferated in the intestines of the P. minimumexposed mussels. Hemocytes within the intestine appeared to be either overwhelmed by the large number of bacteria or fully occupied in the encapsulating response to P. minimum cells; when hemocytes reached the intestine lumina, they underwent apoptosis and bacterial degradation. This experiment demonstrated that M. edulis is affected by ingestion of toxic P. minimum; however, the specific responses observed in the blue mussel differed from those reported for other bivalve species. This finding highlights the need to study effects of HABs on different bivalve species, rather than inferring that results from one species reflect the exposure responses of all bivalves.

Effects of Alexandrium minutum exposure upon physiological and hematological variables of diploid and triploid oysters, Crassostrea gigas

“…Concurrently, an inflammatory response was observed in the mussel alimentary canal (Galimany et al, 2008a). These findings suggested a possible link between changes in digestive-gland lipids and inflammatory response in the same organ.…”

“…In accordance with the above-cited studies, adductor muscles of A. minutum-exposed oysters in the present study were intensely affected by myopathy: myoatrophy, hyaline degeneration and wavy-pattern degeneration. Such changes of muscle tissue structure may be associated with the muscle paralysis observed during Alexandrium exposure in C. virginica and Mytilus edulis Galimany et al, 2008a). Observed myodegeneration may partially explain the modifications in valve activity of oysters exposed to A. minutum (Tran et al, 2010).…”

“…Some recent studies have described inflammatory responses (aggregation/infiltration of hemocytes in organs and/or hemocytes in diapedesis through epithelia) in different tissues of bivalve species exposed to several harmful microalgae (Galimany et al, 2008 a, b and c;Hégaret et al, 2009). Mussels (Mytilus edulis -Linnaeus, 1758) exposed to A. fundyense showed an inflammatory response consisting of diapedesis of hemocytes into the alimentary canal and hemocyte migration into the connective tissue between the gonadal follicles (Galimany et al, 2008a). These findings suggest that harmful-algal exposure can elicit activation of defense or repair mechanisms in response to resulting tissue lesions in bivalves.…”

“…Moreover, inflammatory responses are known to be induced by lipid oxidation in vertebrate models (reviewed in Fantone and Ward, 1982). In mussels (M. edulis) exposed to A. fundyense, increased ceroidosis in tissues was probably attributable to lipid peroxidation generated by ingestion of the harmful alga (Galimany et al, 2008a).…”

Effects of the environment and culture depth on growth and mortality in juvenile Pacific oysters in the Strait of Georgia, British Columbia

“…Harmful algal blooms (HABs) can cause shellfish mortalities by means of oxygen depletion and/or tox in production (Shum way et al 1990, Lands berg 2002. HABs can also re duce shellfish growth rates (Alexander et al 2006) and filtration efficiencies (Gainey & Shumway 1988, Cassis & Taylor 2006, as well as damaging their digestive systems (Keppler et al 2005, Galimany et al 2008). Oysters may succumb to opportunistic viral and bacterial infections during or after periods of heightened environmental and/ or physiological stress (Fried man et al 1991, Cheney et al 2000, Burge et al 2007).…”