Deleterious effects of diatom-derived polyunsaturated aldehydes on early life stages of a marine forage fish

Diatom-derived polyunsaturated aldehydes (PUAs) exert deleterious effects on numerous invertebrate consumers. However, their potential to impair vertebrate physiology and development remains unexplored. Forage fishes are a foundational functional group within marine ecosystems, and in many species, early life stages are sympatric with diatoms. Surf smelt, Hypomesus pretiosus , is a vital forage fish of the Northeast Pacific Ocean. Surf smelt spawn and embryos develop in the upper intertidal zone near benthic diatoms, and larvae undergo metamorphosis nearshore, feeding on plankton that includes diatoms. During these sensitive and transformative periods, surf smelt may experience negative ecotoxicological effects from diatom PUAs. This study investigated the effects of PUAs on the development and physiology of surf smelt embryos and larvae. Across a range of PUA concentrations, we measured embryonic survival, hatching success, heart rate, endogenous energy consumption, morphology, and sensory development at hatching. High PUA exposure increased embryonic mortality and reduced hatching success. Embryo heart rates were not significantly affected by PUA exposure; however, following acute exposure, heart rates showed a progressive decline with increasing concentration. PUA exposure throughout development slowed consumption of endogenous energy reserves and reduced size at hatch. Larvae from embryos reared under high PUA concentrations had smaller eyes, while otic capsule size was unaffected. Collectively, these findings indicate that dissolved PUAs may impair the survival of an ecologically foundational vertebrate during its early development through multiple integrated alterations in developmental trajectories. Given their ecological importance, any factors that reduce the annual recruitment of forage fishes could have cascading effects on marine ecosystems.