Search for: All records

Seasonal upwelling in coastal environments supports high primary production by increasing concentrations of inorganic nutrients in the euphotic zone. Diatoms typically dominate planktonic primary production and community composition during seasonal upwelling, especially in temperate ecosystems. Some diatoms elevate their competitive fitness by producing polyunsaturated aldehydes (PUAs). These phytochemicals act to reduce the fecundity of their grazers by reducing sperm motility, lowering egg production and viability, and delaying embryo development, reducing diatom consumptive pressure. While research into the mechanisms driving PUA production includes bottom-up factors (i.e., nutrient availability), few studies have explored how dissolved carbon dioxide (pCO2) concentration affects PUA production. In this study, we analyzed the production of bioactive PUAs (2,4-heptadienal, 2,4-octadienal, and 2,4-decadienal) in two diatom species found in the Salish Sea, an inland sea of the North Pacific ecosystem, under varying pCO2 concentrations that are experienced during seasonal upwelling events. We found that elevated pCO2 concentration caused an increase in carbon uptake in the diatoms, but did not lead to more PUA production, and at times caused a decrease in production. Our results suggest that carbon enrichment does not elevate the chemically defensive capabilities of diatoms by way of elevated PUA production. 

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. 

Diatoms are key primary producers across marine, freshwater, and terrestrial ecosystems. They are responsible for photosynthesis and secondary production that, in part, support complex food webs. Diatoms can produce phytochemicals that have transtrophic ecological effects which increase their competitive fitness. Polyunsaturated aldehydes (PUAs) are one class of diatom-derived phytochemicals that are known to have allelopathic and anti-herbivory properties. The anti-herbivory capability of PUAs results from their negative effect on grazer fecundity. Since their discovery, research has focused on their production by pelagic marine diatoms, and their effects on copepod egg production, hatching success, and juvenile survival and development. Few investigations have explored PUA production by the prolific suite of benthic marine diatoms, despite their importance to coastal trophic systems. In this study, we tested eight species of benthic diatoms for the production of the bioactive PUAs 2,4-heptadienal, 2,4-octadienal, and 2,4-decadienal. Benthic diatom species were isolated from the Salish Sea, an inland sea within the North Pacific ecosystem. All species were found to be producers of at least two PUAs in detectable concentrations, with five species producing all three PUAs in quantifiable concentrations. Our results indicate that production of PUAs from Salish Sea benthic diatoms may be widespread, and thus these compounds may contribute to benthic coastal food web dynamics through heretofore unrecognized pathways. Future studies should expand the geographic scope of investigations into benthic diatom PUA production and explore the effects of benthic diatoms on benthic consumer fecundity.