Oxylipins and Other Natural Products Produced by UV-sterilization Impact Commercial Oyster Larvae Production in a New England Estuary

Here, oyster larval developmental abnormalities within a New England hatchery were linked to a common UV sterilization technique that has been used for over 20 years. Because of the known link between phytoplankton oxylipins and egg mortality in copepods, we hypothesized that UV pretreatment of seawater results in the production of oxylipins that inhibit larval digestion of microalgae. We used lipidomics to observe changes in the organic compounds dissolved in estuarine seawater when filtered and when filtered and pretreated with UV. UV treatment resulted in an increase in the relative abundance of oxylipins associated with cyanobacteria, fungi, and macroalgae in 2020, whereas oxylipins typically produced by diatoms were more abundant in the UV treatments from 2021. Oxylipin concentrations were higher in 2020, when the hatchery reported the most severe problems with larval development. Removing the UV step allowed continued larval production in both years. However, the lack of UV sterilization led to an unidentified bacterial pathogen in 2021, which nearly decimated the overall seasonal production of oyster seed. To follow up in a more controlled environment, the larvae were exposed to exogenous oxidized lipids, which resulted in the same digestive syndrome and histological symptoms as the endogenous suite of compounds produced by UV. Further investigation of the lipidomes revealed that oxylipins were only one class of potentially harmful compounds linked to UV sterilization, and the dissolved concentrations of secondary metabolites associated with higher plants, a wide range of pharmaceuticals, and anthropogenic organic pollutants also increased under UV light. Future efforts will explore the sources of these compounds, the mechanisms by which they inhibit oysters, and whether this is an emerging environmental problem for other ecosystems and shellfish hatcheries.