Gulf of Alaska | Lower Trophic Levels
Factors influencing the health of farmed Pacific oysters, Magallana gigas , in Southeast Alaska Presenter: Juliana Cornett , juliana.cornett@noaa.gov, NOAA Alaska Fisheries Science Center Rebecca Cates , rebecca.cates@noaa.gov, NOAA Alaska Fisheries Science Center
Muriel Dittrich , mcdittrich@alaska.edu, University of Alaska Fairbanks Courtney Hart , chart16@alaska.edu, University of Alaska Fairbanks Kelly Koehler , kelly.koehler@noaa.gov Meta Mesdag , meta@saltyladyseafood.co Cody Pinger , cody.pinger@noaa.gov, NOAA Alaska Fisheries Science Center Jordan Hollarsm , jordan.hollarsmith@noaa.gov, NOAA Alaska Fisheries Science Center
Mariculture is a rapidly growing industry in Alaska, with farmed Pacific oysters ( Magallana gigas ) currently significantly contributing to this industry’s profit. However, there are no wild oysters in Alaska and the high-latitude estuarine environment of southeast Alaska differs greatly from many other areas in the country where oysters are currently farmed. Therefore, it is important to determine environmental factors that influence oyster health to optimize growing conditions at existing oyster farms and to aid in site selection for future farms as the industry grows. Another challenge associated with farmed oysters is harmful algal blooms (HABs), with paralytic shellfish poisoning (PSP) from Alexandrium spp. diatoms being of particular concern for public health in the region. As part of an ongoing HAB monitoring project, water column and oyster tissue sampling occurs weekly at a local oyster farm in Juneau, Alaska. Temperature, salinity, nutrient concentrations, chlorophyll levels, PSP toxin levels, and phytoplankton community composition are measured at two water column depths. Additionally, oyster tissue is analyzed for PSP toxin levels, as well as for lipid content and fatty acid composition as indicators of oyster health. We observed significant seasonal variation in both environmental variables and phytoplankton community composition in southeast Alaska over the four years of monitoring, both of which may have major impacts on the health of farmed oysters in this region. Water temperature at the farm site ranges from 3 to 18 degrees Celsius throughout the year, while salinity ranges from 5 to 36 parts per thousand, with higher temperatures and lower salinities in the summer months. Summer months also bring higher phytoplankton biomass, especially in the form of diatom blooms, with Thalassiosira, Skeletonema, and Chaetoceros being a few of the dominant genera. Preliminary results suggest that higher lipid content in oysters may align with peaks in phytoplankton biomass, and tends to be higher at higher water temperatures and lower salinities. Thus far, toxin levels in sampled oysters have been below safe thresholds for consumption, but analyses are ongoing to identify drivers of toxicity. Determining which factors contribute most strongly to the health of farmed oysters, as well as to toxin levels in oyster tissue, is critical in allowing oyster mariculture to expand in a safe and profitable way in southeast Alaska.
Alaska Marine Science Symposium 2023 302
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