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PMEL Publications Abstract

FY 2025

Nutrient limitation dampens the response of a harmful algae to a marine heatwave in an upwelling system

Fischer, A.D., E. Houliez, B. Bill, M.T. Kavanaugh, S.R. Alin, A.U. Collins, R.M. Kudela, and S.K. Moore

Limnol. Oceanogr., 70(S1), S69-S85, doi: 10.1002/lno.12604, View open access article at ASLO/Wiley (external link) (2025)

Harmful algal blooms caused by toxin-producing species of the diatom genus Pseudo-nitzschia have been linked to anomalously warm ocean conditions in the Northern California Current System. This study compares summertime concentrations of Pseudo-nitzschia spp. and the toxin they produce, domoic acid, during a marine heatwave year (2019) and a climatologically neutral year (2021). An Imaging FlowCytobot was installed on a fishery survey vessel alongside environmental sensors to continuously sample phytoplankton and oceanographic parameters. This was paired with targeted manual sample collections for nutrients, chlorophyll, and domoic acid. Accumulations of Pseudo-nitzschia spp. were associated with upwelling zones and established hotspot regions: the Juan de Fuca Eddy, Heceta Bank, and Trinidad Head. Overall, however, Pseudo-nitzschia spp. and domoic acid concentrations were low during both summers and appear to have been limited by nitrate. Nutrient availability may therefore modulate the response of Pseudo-nitzschia spp. to warm anomalies. Comparison of these results with 2015, another marine heatwave year but one that produced record concentrations of Pseudo-nitzschia spp. and domoic acid, suggests that the timing of marine heatwave conditions in the nearshore relative to seasonal upwelling plays a key role in determining whether a Pseudo-nitzschia spp. harmful algal bloom will occur.

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