| Description: |
Oceanic high-nitrate, low-chlorophyll environments have been highlighted for potential large-scale iron fertilizations to help
mitigate global climate change. Controversy surrounds these initiatives, both in the degree of carbon removal and
magnitude of ecosystem impacts. Previous open ocean enrichment experiments have shown that iron additions stimulate
growth of the toxigenic diatom genus Pseudonitzschia. Most Pseudonitzschia species in coastal waters produce the
neurotoxin domoic acid (DA), with their blooms causing detrimental marine ecosystem impacts, but oceanic
Pseudonitzschia species are considered nontoxic. Here we demonstrate that the sparse oceanic Pseudonitzschia
community at the high-nitrate, low-chlorophyll Ocean Station PAPA (50° N, 145° W) produces approximately 200 pg DA L
−1 in response to iron addition, that DA alters phytoplankton community structure to benefit Pseudonitzschia, and that
oceanic cell isolates are toxic. Given the negative effects of DA in coastal food webs, these findings raise serious concern
over the net benefit and sustainability of large-scale iron fertilizations.
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