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Shift Towards Syndiniales Prevalence in Protist Communities During a Marine Heatwave
Hanneloor Heynderickx1,2, Ro Allen1, Tina C Summerfield1
1Department of Botany, University of Otago, Dunedin, New Zealand.
Abstract:
Marine heatwaves (MHWs) are becoming more frequent and severe, yet their impact on natural marine protist communities remains poorly understood. Using 18S rRNA gene amplicon sequencing, we examined the effects of the extreme 2017/2018 Austral summer MHW on protist communities in three water masses off the southeast coast of New Zealand. During the MHW, alpha diversity declined significantly in Subtropical Waters (Shannon: 1.78 ± 0.42, p = 0.03) and the Front (Shannon: 3.26 ± 0.19, p = 0.05), driven by reduced evenness in Subtropical Waters (Pielou: 0.36 ± 0.06, p = 0.03) and by both richness and evenness in the Front. Communities also became more homogeneous, with lower dispersion among samples, and the water mass driven structuring of communities seen in non-MHW summers disappeared during the MHW. The taxonomic composition shifted substantially: the parasitic dinoflagellate Syndiniales became the most dominant group in Subtropical Waters and the Southland Front (up 68 and 30 percentage points, respectively), while Dinophyceae decreased by 47% and 20%, respectively. Since host-parasitoid interactions play a significant role in carbon and nutrient cycling, the strong increase in relative abundance of Syndiniales underscores the need to consider biotic interactions, including host-parasitoid relationships, when studying MHW impacts on marine protists.
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