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Rapid downward transport of the neurotoxin domoic acid in coastal waters


Toxic phytoplankton blooms threaten coastlines worldwide by diminishing beach quality and adversely affecting marine ecosystems and human health1,2. The common diatom genus Pseudo-nitzschia consists of several species known to produce the neurotoxin domoic acid3. Recent studies suggest that algal blooms dominated by Pseudo-nitzschia are increasing in frequency and duration owing to changes in coastal nutrient regimes1,4,5. However, few studies have examined the persistence or long-term biogeochemical cycling of domoic acid in marine waters6,7,8. Here, we measure the concentration of domoic acid in surface waters and sediment traps—up to 800 m in depth—off the coast of Southern California. We show that peaks in Pseudo-nitzschia abundance and domoic acid concentrations in surface waters coincide with peaks in diatom and toxin abundance at depth, suggesting rapid downward transport of the toxin. In some cases, the sinking particles contain over five times the United States federal limit of domoic acid. Detection of domoic acid in bottom sediments indicates that the toxin may persist long after the Pseudo-nitzschia blooms. Our results indicate that vertical fluxes of domoic acid are a substantial source of the toxin to deep-ocean food webs, and could explain high levels of domoic acid previously observed in benthic organisms9,10.

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Figure 1: Santa Barbara Basin (SBB) and San Pedro Basin (SPB) sampling sites.
Figure 2: Domoic acid and Pseudo-nitzschia cell measurements in sediment-trap material and surface waters of Santa Barbara Basin.
Figure 3: Domoic acid in sediment-trap material and surface waters of San Pedro Basin.
Figure 4: Comparison of Pseudo-nitzschia bloom and non-bloom events.


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We thank A. Michaels and D. Capone for the use of the SPB sediment traps; D. Hammond for help in processing SPB sediment-trap samples; E. Tappa for his help in deployments and recoveries of the SBB trap; N. Guillocheau and the Channel Islands National Marine Sanctuary for help with SBB water collections; R. Kudela for providing laboratory facilities for Pseudo-nitzschia and DA analyses of surface SBB water samples and J. Gully, C. Tang and the Los Angeles County Sanitation Districts for providing sediment core samples. This work was supported by NSF OCE 0351169 and OCE 0850425, EPA RD-83170501, NOAA NA160P2790, NOAA Sea Grant NA06OAR4170012 and NASA NNX08AG82G.

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E.S.-W., A.S. and C.R.B.-N. measured DA concentrations, conducted Pseudo-nitzschia cell counts and handled data interpretation for the SBB and SPB datasets. J.M.B. and J.L.F. helped in the development of the LC-MS/MS method for SBB. S.L.M. provided SEM images. C.A. provided surface DA and Pseudo-nitzschia cell concentrations for SBB. E.F. measured DA with ELISA kits on SPB samples. R.S. and I.C. assisted sampling collection throughout the covered time period in the SPB area. R.T. and W.M.B. provided sediment-trap samples in SBB and SPB, respectively. D.A.C., B.H.J., P.E.M. and D.A.S. provided support and infrastructure for the SPB Pseudo-nitzschia and DA measurements.

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Correspondence to Claudia R. Benitez-Nelson.

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Sekula-Wood, E., Schnetzer, A., Benitez-Nelson, C. et al. Rapid downward transport of the neurotoxin domoic acid in coastal waters. Nature Geosci 2, 272–275 (2009).

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