Climate change, specifically increased atmospheric carbon dioxide (CO2), has profoundly altered global ecosystems, leading, among other things, to increased sea surface temperatures and levels, ocean acidification, and greater prevalence of waterborne diseases. In the past two decades, this shift in ocean conditions has contributed to more frequent harmful algal blooms (HABs) along coastal areas, raising concerns about the threats that HABs pose to shellfish aquaculture.
Shellfish aquaculture is valuable ecologically for its role in sustaining healthy marine ecosystems, and economically for being a source of food. In the United States, the Pacific oyster Magallana gigas is a commercially valuable shellfish species by weight but is threatened by recurring summer mortality events. These events have primarily been attributed to infectious pathogens, such as Ostreid herpesvirus-1 and Vibrio spp., as well as to elevated seawater temperatures. Recently, HABs have gained attention for their potential, yet less known, role in these mortality events. Toxins produced by HAB species can adversely affect aquatic and terrestrial animals. Research indicates that HAB toxins can impact shellfish by affecting their feeding, morphology, growth, reproduction, and survival at both juvenile and adult stages. While there are indicators suggesting a correlation between HABs and summer mortalities in Pacific oysters, a definitive link has not yet been established.
We are investigating the physiological effects of a toxin-producing algae (Alexandrium catenella) on juvenile Pacific oysters. Our objectives include assessing survival, growth, and gene expression patterns in juvenile Pacific oysters upon laboratory exposure to A. catenella. The goal is to determine whether these exposures increase Pacific oysters’ susceptibility to summer mortality through physiological changes.
Juvenile oysters (n = 25) will be placed in 3L tanks, each fitted with a magnetic stirrer, a mesh barrier, and artificial seawater at 22°C. Following starvation for 24 h, oysters will be treated with either toxic Alexandrium sp., non-toxic Alexandrium sp., a dietary algal mix of Nannochloropsis spp., or no algae for 72 h. Each treatment will be replicated in three separate tanks, totaling 12 tanks. Mortalities will be monitored daily, and oysters (n = 5) and water samples will be collected every 24 h. Toxin concentration in both oyster and water samples will be measured with a Saxitoxin (PSP) Enzyme-Linked Immunosorbent Assay (ELISA) kit. Oyster RNA will be evaluated for quality and submitted for sequencing. Preliminary results will be presented.