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Anthropogenic climate change is projected to affect marine ecosystems by challenging the environmental tolerance of individuals. Marine fishes may be particularly vulnerable to emergent climate stressors during early life stages. Here we focus on embryos of Pacific herring(Clupea pallasii), an important forage fish species widely distributed across the North Pacific. Embryos were reared under a range of temperatures (10-16°C) crossed with twopCO2levels (600 and 2000μatm) to investigate effects on metabolism and survival. We further tested how elevatedpCO2affects critical thermal tolerance (CTmax) by challenging embryos to short-term temperature fluctuations. Experiments were repeated on embryos collected from winter and spring spawning populations to determine if spawning phenology corresponds with different limits of environmental tolerance in offspring. We found that embryos could withstand acute exposure to 20°C regardless of spawning population or incubation treatment, but that survival was greatly reduced after 2-3 hours at 25°C. We found thatpCO2had limited effects onCTmax. The survival of embryos reared under chronically warm conditions (12°, 14°, or 16°C) was significantly lower relative to 10°C treatments in both populations. Oxygen consumption rates (MO2) were also higher at elevated temperatures andpCO2levels. However, heart contraction measurements made 48 hours afterCTmaxexposure revealed a greater increase in heart rate in embryos reared at 10°C compared to 16°C, suggesting acclimation at higher incubation temperatures. Our results indicate that Pacific herring are generally tolerant ofpCO2but are vulnerable to acute temperature stress. Importantly, spring-spawning embryos did not clearly exhibit a higher tolerance to heat stress compared to winter offspring.
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This content will become publicly available on November 7, 2025
The Effects of Diatom-Derived Polyunsaturated Aldehydes on Embryonic and Larval Surf Smelt (Hypomesus pretiosus) Fitness.
Polyunsaturated aldehydes (PUAs) are secondary oxylipins produced by some diatoms. PUAs are produced at a greater rate when diatom cells are damaged, suggesting that they may act as chemical grazing deterrents. Past studies showed the deleterious effects of particulate PUAs on diatom consumers like copepods and marine invertebrates. However, to date, very few studies have explored the potential for diatom-derived PUAs to affect marine vertebrates, such as forage fishes. Forage fishes are a foundational functional group in marine ecosystems whose early life history stages are often sympatric with diatoms due to their nearshore spawning behavior and planktivorous diet. In this study, I addressed the question of whether PUAs detrimentally affect a common Salish Sea forage fish, the surf smelt (Hypomesus pretiosus; Girard 1854). The project focused on determining whether PUAs affect the development and physiology of surf smelt embryos and larvae. This was done by measuring survival and hatch success rates, embryonic heart rates, usage of endogenous energy reserves, and morphological features at hatch. Higher concentrations of PUAs resulted in higher mortality and lower hatch success rates of embryonic surf smelt. Embryonic heart rates were equivalent among treatments when embryos were exposed to PUAs soon after fertilization, suggesting that surf smelt embryos can acclimate to PUAs if exposed during early development. However, higher concentrations of PUAs significantly lowered the heart rates of embryos that were exposed to PUAs days after fertilization. Exposure to PUAs diminished the consumption rate of endogenous energy reserves, and the overall size of surf smelt at hatch was reduced. Our results indicate that exposure to dissolved PUAs could impair the fitness of ecologically foundational forage fish early life history stages. Negative effects that manifest into low adult population sizes will have cascading effects on marine ecosystems.
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- Award ID(s):
- 2342375
- PAR ID:
- 10638936
- Publisher / Repository:
- Western Washington University Graduate School Collection
- Date Published:
- Format(s):
- Medium: X
- Institution:
- Western Washington University
- Sponsoring Org:
- National Science Foundation
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