Simultaneous Occurring Heatwaves and Cyanobacteria Blooms Alter Polyunsaturated Fatty Acid Transfer in a Brackish Trophic Cascade

Abstract

With climate change, marine heatwaves become more frequent and may favour the emergence of cyanobacterial blooms. Because cyanobacteria lack long-chain polyunsaturated fatty acids, they provide poor dietary quality for consumers, potentially altering the fatty acid composition of primary consumers and propagating nutritional stress through food webs. We examined how a simulated heatwave (12 °C to 18 °C) and an associated cyanobacterial bloom-like dominance may affect trophic transfer from phytoplankton to the herbivorous rotifer Brachionus plicatilis and further to its predator, the mysid Neomysis integer. Rotifers were fed either high-quality algae or a low-quality cyanobacteria-dominated diet mixture. Rotifers were then rinsed to remove external residual phytoplankton and subsequently offered as prey to mysids. We analyzed the fatty acid profiles of both rotifers and mysids and monitored mysid survival. High temperature and the presence of cyanobacteria at the base of the food web reduced mysid survival. Both factors also influenced the fatty acid composition of rotifers and mysids. For mysids at the third trophic level, warming modulated how strongly diet quality affected their fatty acid profile. These results suggest that concurrent heatwaves and cyanobacterial blooms may intensify cyanobacteria’s negative impacts on food webs by altering the transfer of key fatty acids across trophic levels.

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