During the summer of 2017, recurrent extensive blooms of the diazotrophic cyanobacterium Trichodesmium invaded the beaches and coastal waters of the Canary Islands, causing great social alarm. Some local media and public sectors ascribed, without any strong scientific evidence, the origin and reactivation of these blooms to untreated sewage outfalls distributed along the coasts. In order to test whether sewage outfalls could have any influence on the metabolic activity of Trichodesmium, we performed 13C and 15N2 uptake experiments with colonies experiencing three different bloom development stages, incubated both with clear seawater and sewage water from an outfall south of Gran Canaria island. Our results showed that sewage outfalls did not promote any increase in dinitrogen (N2) fixation in Trichodesmium, supporting the hypothesis that decaying blooms were generated offshore and transported shoreward by local currents and winds, accumulating mostly leeward of the islands. The combination of unusually warm seawater temperatures, enhanced and sustained stratification of the upper water column and recurrent dust deposition events would have favored the development of the Trichodesmium blooms, which lasted for at least four months.
Trichodesmium is a colonial filamentous cyanobacterium capable of atmospheric dinitrogen (N2) fixation. It abounds in subtropical and tropical oceanic waters, often forming blooms large enough to be detected by satellite images1, rendering a source of fixed nitrogen that fuels primary production significantly2. Its growth may be limited however by the availability of iron3 and phosphorus4,5,6. In the open waters of the subtropical North Atlantic Ocean, the seasonal meridional shift of the North African dipole controls the deposition of iron-rich Saharan dust on surface waters7. Dust events are known to enhance the proliferation and diazotrophic activity of Trichodesmium leading to the formation of massive blooms8,9,10,11, with colonies adopting three-dimensional shapes known as "puffs" or “tufts”. Their organic matter coating as well as the microbial epibiont community provide Trichodesmium colonies the ability to degrade atmospheric dust particles to obtain the iron they contain12,13, which is likely not possible for free single Trichodesmium filaments14.
Although it is not clear what mechanism, or combination of mechanisms, triggers the development of Trichodesmium blooms, warm (> 20 °C) and stratified waters as well as the availability of phosphorus and iron, are essential requirements to sustain extensive blooms15. Under such conditions, Trichodesmium develops swiftly, fixing high amounts of carbon and nitrogen16. This intense activity may exhaust limiting nutrients, forcing Trichodesmium filaments to release exopolymeric substances while aggregating and forming dense colonies17. This strategy optimizes nutrient uptake and repartition of resources between filaments of a same colony17,18. When all limiting resources are depleted, Trichodesmium cells induce apoptosis, also referred to as programmed cell death (PCD)19, a process that can make Trichodesmium blooms almost disappear in a matter of hours to days20.
Traditionally considered an autotroph16, Trichodesmium is now known to use dissolved organic matter (DOM) molecules which may provide it with alternative nutrient resources when their inorganic forms are unavailable or their use becomes too energetically demanding. Trichodesmium is able to use dissolved organic phosphorus (DOP) forms including phosphoesters and phosphonates when inorganic phosphate availability is low5,6. The RuBisCo enzyme of Trichodesmium has a low affinity for CO221, which is thought to explain its enhanced carbon fixation when exposed to high CO2 levels and/or lower pH22,23. The inefficiency of RuBisCo may drive Trichodesmium to use DOM to meet its carbon needs. For example, natural Trichodesmium colonies from the Southwest Pacific Ocean have been observed to obtain as much carbon via amino acids as via CO224. Cultures of Trichodesmium have been reported to grow faster on combined nitrogen forms such as urea than on N225. More recent laboratory experiments have shown that when grown under limiting concentrations of iron and/or phosphorus, Trichodesmium downregulates N2 fixation and obtains nitrogen from trimethylamine or ammonium26. Collectively, these studies suggest that Trichodesmium adopts a mixotrophic nutrition mode when its basic metabolic activities are reduced due to environmental stress or a limitation of resources. Mixotrophy thus confers Trichodesmium metabolic plasticity and adaptation to dynamic environmental nutrient scenarios.
Throughout the summer of 2017, recurrent blooms of Trichodesmium were observed in coastal and offshore waters around the Canary Islands27. These blooms appeared first in the western side of the archipelago, coinciding with dense Saharan dust deposition events, enhanced water column stratification and seawater temperatures > 23 °C, later spreading to the eastern side of the archipelago, when those conditions extended eastwards27. The massive accumulations of Trichodesmium along the coasts of the Canary Islands (see Fig. 1) caused great social alarm, and were attributed by some media and public sectors to uncontrolled sewage outfalls28, for which the Spanish Government has been sued by the European Commission29. The attribution was partly based on a recent coastal study in the eastern Mediterranean Sea, that reported an increase in the abundance and N2 fixation activity of Trichodesmium after a sporadic outburst of a local wastewater treatment plant30. In this study the authors suggested that, due to the low N2 fixation activity measured, Trichodesmium could have shifted to a mixotrophic nutrition using wastewater-derived DOM compounds. Although the magnitude of the bloom in the Canary Islands was orders of magnitude larger in terms of density compared to that of the Mediterranean Sea26, we wanted to verify whether wastewater outfalls could have promoted or helped maintain Trichodesmium blooms in the nearshore waters of the Canary Islands. With this aim, we collected Trichodesmium colonies at different stages of development of the bloom (Fig. 2), and performed incubations with clear seawater and wastewater from an urban sewage outfall to the south of Gran Canaria Island and examined its impact on N2 and carbon fixation rates.
Results and discussion
We incubated Trichodesmium from three different bloom development stages (sparse, slick and PCD-like, Fig. 2) with clear and sewage waters. Our experiments showed that N2 fixation rates in clear water incubations were not significantly different from those of sewage incubations (Fig. 3, t-test p = 0.98), which indicates that sewage did not promote N2 fixation in Trichodesmium. The concentrations of dissolved organic carbon (DOC) and nitrogen (DON) in sewage waters were double than in clear waters (Table 1), which is likely responsible for the increase in bacterial abundance in sewage waters with respect to clear waters (Table 2). In support of these results, the abundance of the most active high nucleic acid bacteria (HNA) tripled when incubated with sewage for 24 h (Fig. 4e) coinciding with a net consumption of DOC (Fig. 4f), a trend which was not observed in clear water incubations (Fig. 4b,c). Trichodesmium could have responded positively to DOP inputs as observed elsewhere31,32, but in our study DOP concentrations of clear and sewage waters were not significantly different (Table 1). We cannot exclude however, the possibility that there were toxic components in sewage waters that may have locally promoted the death of Trichodesmium close to the coast, as wastewaters are known to impair the metabolic activity of phytoplankton33.
N2 fixation rates were ~ 200, 70 and 2 nmol N L−1 day−1 in sparse, slick and PCD samples, respectively, in both clear or sewage water incubations (Fig. 3a,b). We confidently attribute these rates to Trichodesmium, since our incubations included concentrated Trichodesmium biomass and clear or sewage water prefiltered by 20 µm (see “Methods”). Diazotrophs smaller than 20 µm such as UCYN-A have been reported in the surroundings of the Canary Islands34, but their N2 fixation activity is one to two orders of magnitude lower than that measured here. Our N2 fixation rates were three, two and one order of magnitude higher than those observed during a sewage outburst in the eastern Mediterranean Sea30. The N2 fixation rates of sparse colonies were at the high end of volumetric rates compiled in the global N2 fixation database35, and in the range of those observed in hotspots of diazotrophy such as the western tropical South Pacific36. This indicates that Trichodesmium were healthy and active at the time of sampling. Between June and August 2017, the Canary Islands experienced optimal conditions for the development of Trichodesmium: unusually warm seawater temperatures (> 23 °C), enhanced stratification of the water column and several dust deposition peaks superimposed on a lower but steady dust supply throughout the summer months27. There was no evidence that Trichodesmium consumed DOC and DON despite their higher concentrations in sewage waters than in clear waters (Table 1). This agrees with previous studies that point towards a mixotrophic nutrition in Trichodesmium only when inorganic nutrients are not available24,26.
The N2 fixation rates of the three bloom development stages were significantly different (one-way ANOVA p = 1.5 × 10–5 and p = 0.003 for clear and sewage waters, respectively). This sequential decrease in N2 fixation between bloom development stages agrees well with those observed in culture and field experiments19,20,37,38, and is clearly depicted by an increase in the release of PO43−, NH4+ and DOC as cells die and the bloom decays (Table 1).
Carbon fixation rates were not significantly different between clear and sewage water incubations either (t-test, p = 0.07). Contrary to N2 fixation rates, carbon fixation was 1.4 and ~ 2 times higher in slick samples than in sparse stages in clear and sewage water incubations, respectively (Fig. 3c,d). However, this enhancement was only statistically significant in clear water incubations (one-way ANOVA p = 0.0002). Carbon fixation is performed by the bulk phytoplanktonic community and not only by Trichodesmium, however, the abundance of picophytoplankton in slick samples was not higher than that observed in the other bloom stages (Table 2).
The recurrent PCD-like status of the Trichodesmium accumulations observed along the Canary Islands’ coasts in the summer of 2017 (Fig. 1) further reinforce our hypothesis that sewage outfalls were not causing bloom reactivation and raises the question of whether they were, on the contrary, toxic to Trichodesmium. We however note that the chemical composition of sewage waters may be highly variable depending on their source (e.g. urban vs. rural domestic sewage, hotel resorts, golf courses, desalinization plants, etc.), potentially leading to differences in their impact on bacteria, non N2 fixing phytoplankton and diazotrophs.
In conclusion, our results support the hypothesis that sewage outfalls south of the islands did not trigger the formation of new blooms, nor sustain or enhance blooms originated previously offshore. Although this study examines only the potential effects of sewage waters on the growth of Trichodesmium, other results (which will form the basis of a complementary paper) provide evidence that the 2017 bloom originated in open ocean waters of a large part of the Canary Current region, and the colonies were transported towards the coasts by the regional circulation and local winds. The progression from sparse colonies in open ocean waters, followed by surface slicks nearer the islands to finally decaying blooms accumulated in the lee of the islands strongly supports this hypothesis27.
Trends in ocean temperature in the past two decades39 indicate that the surface waters of the Canary Current are warming unabatedly, presumably favoring the more common appearance of Trichodesmium blooms in the near future. This has unknown consequences for the Canary region, as blooms have also occurred in the years 2018–2020, although with less intensity than in 2017. In order to predict the development of these blooms it is therefore necessary to determine which factors (or combination of factors) trigger and maintain the blooms from their origin to their collapse. The results of this study shed some light on this issue by clearly showing that coastal sewage outfalls do not enhance or maintain these blooms near the coast.
Carbon and N 2 fixation measurements
In order to test the effects of sewage waters on the N2 and carbon fixation activity of Trichodesmium, we sampled colonies from near surface waters south of Gran Canaria Island in September 2017 (Table 1). To evaluate the behavior of colonies experiencing different developmental stages, we sampled waters with Trichodesmium under three different bloom development phases (Fig. 2): (i) sparse colonies -’sparse’-, (ii) colonies accumulated in the surface as slicks-’slick’-, and (iii) collapsing accumulated colonies -’PCD-like’-, collected at three different locations south of Gran Canaria Island (Table 1). Clear seawater devoid of Trichodesmium colonies was sampled further offshore and sewage water was collected from a coastal outlet off Puerto Rico village (27° 47′ 17″ N 15° 42′ 40″ W, Table 1). In situ temperature was measured using a Hydrolab LH4 probe.
Sparse, slick and PCD-like colonies were concentrated using a 20 µm mesh sieve. Subsequently, 5 mL of the concentrate was distributed in triplicate acid-washed 2.3 L polycarbonate bottles (Nalgene) containing either clear seawater or sewage water from separate coastal areas (Table 1), previously filtered through 20 µm mesh to remove predators. Each bottle was spiked with 2.5 mL 15N2 (98 atom %, Euriso-top) and 13C-labeled bicarbonate (NaH13CO3; ≥ 98 atom %, Sigma Aldrich, 10 atom % final enrichment) as previously described40. The bottles were incubated in shaded incubators with surface seawater for 24 h. At the end of incubations, the content of the bottles was filtered through pre-combusted (5 h, 450 °C) GF/F filters (Whatman) and stored at – 20 °C until analysis. The concentration of particulate nitrogen and carbon as well as the isotopic ratio of samples (15N/14N and 13C/12C) were obtained by means of a Thermo Flash 1112 elemental analyzer interfaced by a Conflo III with a Thermo Delta V Advantage isotope ratio mass spectrometer. To ensure an accurate calculation of N2 fixation rates, background dissolved 15N atom % enrichments were determined in all incubations by membrane inlet mass spectrometry as previously described41.
Nutrient and dissolved organic matter concentrations
Seawater samples for the analysis of inorganic nutrients and dissolved organic nitrogen and phosphorus (DON and DOP, respectively) were collected from clear waters, sewage-affected waters and within the Trichodesmium blooms (sparse, slick and PCD-like, see above). Samples for the determination of dissolved organic carbon (DOC) concentrations were collected from within Trichodesmium blooms as above, but also at the start and end of incubations for carbon and N2 fixation measurements. All samples were filtered through pre-combusted GF/F filters (Whatman) before storage at – 20 °C.
Samples for the analysis of nitrate and nitrite (NO3− + NO2−), phosphate (PO43−) and ammonium (NH4+) were collected in 15 mL polyethylene tubes and stored at − 20 °C. Nutrient concentrations were determined using a Technicon II segmented-flow autoanalyzer. Samples for DOC analyses were collected in HCl-washed 20 mL polycarbonate tubes (Nalgene), stored at – 20 °C, and DOC concentrations determined with a TOC-V Shimadzu as detailed in Santana-Falcón et al.42. DON and DOP concentrations were collected in 50 mL polyethylene tubes and analyzed by the wet oxidation of total dissolved nitrogen and phosphorus (TDN and TDP, respectively), with subsequent subtraction of NO3− + NO2− and PO43− concentrations, respectively using standard wet oxidation methods43.
Autotrophic and heterotrophic picoplankton
Abundances of autotrophic (Prochlorococcus and Synechococcus type cyanobacteria and pigmented picoeukaryotes) and heterotrophic prokaryote assemblages were determined by flow cytometry. Samples (1.6 mL) were preserved with paraformaldehyde (2% final concentration), left 15 min at 4 °C in the dark to fix, deep frozen in liquid nitrogen and stored at – 80 °C until analyzed. Fixed samples were thawed, stained in the dark for a few minutes with a DMS-diluted SYTO-13 (Molecular Probes Inc.) stock (10:1) at 2.5 µM final concentration, and run through a BD FACSCalibur cytometer with a laser emitting at 488 nm. High and Low Nucleic Acid content prokaryotes (HNA, LNA) were identified in bivariate scatter plots of side scatter (SSC-H) versus green fluorescence (FL1-H). Autotrophic picoplankton were discriminated in plots of orange fluorescence (FL2) versus red fluorescence (FL3) and picocyanobacteria (Prochlorococcus and Synechococcus) were subtracted from HNA prokaryote counts. Samples were run at low or medium speed until 10.000 events were captured. A suspension of yellow–green 1 µm latex beads (105–106 beads ml−1) was added as an internal standard (Polysciences, Inc.).
Dupouy, C. et al. Satellite captures Trichodesmium blooms in the Southwestern Tropical Pacific. Eos Trans. Am. Geophys. Union 81, 13 (2000).
Capone, D. G. et al. Nitrogen fixation by Trichodesmium spp.: An important source of new nitrogen to the tropical and subtropical North Atlantic Ocean. Glob. Biogeochem. Cycles 19, 1–17 (2005).
Berman-Frank, I., Cullen, J. T., Shaked, Y., Sherrell, R. M. & Falkowski, P. G. Iron availability, cellular iron quotas, and nitrogen fixation in Trichodesmium. Limnol. Oceanogr. 46, 1249–1260 (2001).
Dyhrman, S. T., Webb, E. A., Anderson, D. M., Moffett, J. W. & Waterbury, J. B. Cell-specific detection of phosphorus stress in Trichodesmium from the Western North Atlantic. Limnol. Oceanogr. 47, 1832–1836 (2002).
Dyhrman, S. T. & Haley, S. T. Phosphorus scavenging in the unicellular marine diazotroph Crocosphaera watsonii. Appl. Environ. Microbiol. 72, 1452–1458 (2006).
Dyhrman, S. T. et al. Phosphonate utilization by the globally important marine diazotroph Trichodesmium. Nature 439, 68–71 (2006).
Rodríguez, S. et al. Modulation of Saharan dust export by the North African dipole. Atmos. Chem. Phys. 15, 7471–7486 (2015).
Moore, C. M. et al. Large-scale distribution of Atlantic nitrogen fixation controlled by iron availability. Nat. Geosci. 2, 867–871 (2009).
Langlois, R. J., Mills, M. M., Ridame, C., Croot, P. & LaRoche, J. Diazotrophic bacteria respond to Saharan dust additions. Mar. Ecol. Prog. Ser. 470, 1–14 (2012).
Ratten, J. M. et al. Sources of iron and phosphate affect the distribution of diazotrophs in the North Atlantic. Deep. Res. Part II Top. Stud. Oceanogr. 116, 332–341 (2015).
Capone, D. G. An iron curtain in the Atlantic Ocean forms a biogeochemical divide. Proc. Natl. Acad. Sci. https://doi.org/10.1073/pnas.1322568111 (2014).
Rubin, M., Berman-Frank, I. & Shaked, Y. Dust-and mineral-iron utilization by the marine dinitrogen-fixer Trichodesmium. Nat. Geosci. 4, 529–534 (2011).
Polyviou, D. et al. Desert dust as a source of iron to the globally important Diazotroph Trichodesmium. Front. Microbiol. 8, 1–12 (2018).
Benavides, M., Arístegui, J., Agawin, N., Cancio, J. L. & Hernández-León, S. Enhancement of nitrogen fixation rates by unicellular diazotrophs vs. Trichodesmium after a dust deposition event in the Canary Islands. Limnol. Oceanogr. https://doi.org/10.4319/lo.2013.58.1.0267 (2013).
Bergman, B., Sandh, G., Lin, S., Larsson, J. & Carpenter, E. J. Trichodesmium—A widespread marine cyanobacterium with unusual nitrogen fixation properties. FEMS Microbiol. Rev. https://doi.org/10.1111/j.1574-6976.2012.00352.x (2012).
Capone, D. G., Zehr, J. P., Paerl, H. W., Bergman, B. & Carpenter, E. J. Trichodesmium, a globally significant marine cyanobacterium. Science (80-). https://doi.org/10.1126/science.276.5316.1221 (1997).
Tzubari, Y., Magnezi, L., Be’er, A. & Berman-Frank, I. Iron and phosphorus deprivation induce sociality in the marine bloom-forming cyanobacterium Trichodesmium. ISME J. 12, 1682–1693 (2018).
Mulholland, M. R. & Capone, D. G. The nitrogen physiology of the marine N2-fixing cyanobacteria Trichodesmium spp.. Trends Plant Sci. 5, 148–153 (2000).
Berman-Frank, I., Bidle, K. D., Haramaty, L. & Falkowski, P. G. The demise of the marine cyanobacterium, Trichodesmium spp., via an autocatalyzed cell death pathway. Limnol. Oceanogr. https://doi.org/10.4319/lo.2004.49.4.0997 (2004).
Spungin, D. et al. Mechanisms of Trichodesmium demise within the New Caledonian lagoon during the VAHINE mesocosm experiment. Biogeosciences https://doi.org/10.5194/bg-13-4187-2016 (2016).
Tchernov, D. & Lipschultz, F. Carbon isotopic composition of Trichodesmium spp. colonies off Bermuda: Effects of colony mass and season. J. Plankton Res. 30, 21–31 (2008).
Levitan, O. et al. Elevated CO2 enhances nitrogen fixation and growth in the marine cyanobacterium Trichodesmium. Glob. Change Biol. 13, 531–538 (2007).
Boatman, T. G., Mangan, N. M., Lawson, T. & Geider, R. J. Inorganic carbon and pH dependency of photosynthetic rates in Trichodesmium. J. Exp. Bot. 69, 3651–3660 (2018).
Benavides, M., Berthelot, H., Duhamel, S., Raimbault, P. & Bonnet, S. Dissolved organic matter uptake by Trichodesmium in the Southwest Pacific. Sci. Rep. 7, 1–6 (2017).
Mulholland, M. R., Ohki, K. & Capone, D. G. Nitrogen Utilization and metabolism relative to patterns of N2 fixation in cultures of Trichodesmium Nibb1067. J. Phycol. 35, 977–988 (1999).
Walworth, N. G. et al. Nutrient co-limited Trichodesmium as nitrogen source or sink in a future ocean. Appl. Environ. Microbiol. https://doi.org/10.1128/AEM.02137-17 (2017).
Arístegui, J., Ramos, A. G. & Benavides, M. Informe sobre la presencia de Trichodesmium spp. en aguas de Canarias, en el verano de 2017. https://www3.gobiernodecanarias.org/sanidad/scs/content/cca93804-a35c-11e7-8b56-bf65dd086cd4/InformePresenciaTrichodesmiumspp.pdf (2017).
Gobierno de Canarias. Actualización del censo de vertidos desde tierra al mar en canarias Memoria Detallada: Isla de Gran Canaria. https://opendata.gobiernodecanarias.org/dataset/actualizacion-del-censo-de-vertidos-desde-tierra-al-mar-ano-2017 (2017).
CJEU. On account of its delay in implementing the Urban Waste Water Treatment Directive, Spain is ordered to pay a lump sum of €12 million and a penalty payment of almost €11 million per six-month period of delay. Court Justice Eur. Union. Judgment in Case C-205/17. Commission v Spain. https://curia.europa.eu/jcms/upload/docs/application/pdf/2018-07/cp180120en.pdf (2018).
Rahav, E. & Bar-Zeev, E. Sewage outburst triggers Trichodesmium bloom and enhance N2 fixation rates. Sci. Rep. 7, 1–8 (2017).
Benavides, M. et al. Dissolved organic matter stimulates N2 fixation and nifH gene expression in Trichodesmium. FEMS Microbiol. Lett. 367, 1–8 (2020).
Benavides, M. et al. Dissolved organic matter influences N2 fixation in the New Caledonian Lagoon (Western Tropical South Pacific). Front. Mar. Sci. https://doi.org/10.3389/fmars.2018.00089 (2018).
MacIsaac, J. J., Dugdale, R. C., Huntsman, S. A. & Conway, H. L. The effect of sewage on uptake of inorganic nitrogen and carbon by natural populations of marine phytoplankton. J. Mar. Res. 37, 51–66 (1979).
Agawin, N. S. R. et al. Dominance of unicellular cyanobacteria in the diazotrophic community in the Atlantic Ocean. Limnol. Oceanogr. https://doi.org/10.4319/lo.2014.59.2.0623 (2014).
Luo, Y.-W. et al. Database of diazotrophs in global ocean: abundance, biomass and nitrogen fixation rates. Earth Syst. Sci. Data 4, 47–73 (2012).
Bonnet, S., Caffin, M., Berthelot, H. & Moutin, T. Hot spot of N2 fixation in the western tropical South Pacific pleads for a spatial decoupling between N2 fixation and denitrification. Proc. Natl. Acad. Sci. https://doi.org/10.1073/pnas.1619514114 (2017).
Spungin, D. et al. Programmed cell death in diazotrophs and the fate of organic matter in the Western Tropical South Pacific Ocean during the OUTPACE cruise. Biogeosciences 15, 3893–3908 (2018).
Bar-Zeev, E., Avishay, I., Bidle, K. D. & Berman-Frank, I. Programmed cell death in the marine cyanobacterium Trichodesmium mediates carbon and nitrogen export. ISME J. https://doi.org/10.1038/ismej.2013.121 (2013).
Santana-Falcón, Y. et al. Coastal-offshore exchange of organic matter across the Cape Ghir filament (NW Africa) during moderate upwelling. J. Mar. Syst. 154, 233–242 (2016).
Berthelot, H., Benavides, M., Moisander, P. H., Grosso, O. & Bonnet, S. High-nitrogen fixation rates in the particulate and dissolved pools in the Western Tropical Pacific (Solomon and Bismarck Seas). Geophys. Res. Lett. https://doi.org/10.1002/2017GL073856 (2017).
Kana, T. M., Darkangelo, C., Hunt, M. D., Oldham, J. B., Bennett, G. E. & Cornwell, J. C. Membrane inlet mass spectrometer for rapid high-precision determination of N2, O2, and Ar in environmental water samples. Anal. Chem. https://doi.org/10.1021/ac00095a009 (1994).
Santana-Falcón, Y., Álvarez-Salgado, X. A., Pérez-Hernández, M. D., Hernández-Guerra, A., Mason, E. & Arístegui, J. Organic carbon budget for the eastern boundary of the North Atlantic subtropical gyre: major role of DOC in mesopelagic respiration. Sci. Rep. https://doi.org/10.1038/s41598-017-10974-y (2017).
Pujo-Pay, M. & Raimbault P. Improvement of the wet oxidation procedure for simultaneous determination of particulate organic nitrogen and phosphorous collected on filters. Mar. Ecol. Prog. Ser. 105, 203–207 (1994).
This work was funded by the General Directorate for Nature Protection, Deputy Ministry of the Environment of the Canary Government, and co-funded by the FEDER Canarias Operational Program (2014–2020). Thank you to the General Directorate of Fisheries for the provision of a boat to carry out the sampling, to the crew of the GMR company, and to the Emergency and Rescue Group of the Canary Government (GES). Thanks also to the group of Biological Oceanography (IOCAG), the Spanish Bank of Algae (BEA) and Ellittoral, for their support at sea and in the lab, and to Oliver Grosso (MIO, France) for MIMS analyses. Special thanks to Rogelio Herrera, for his invaluable help during all the phases of the experiment, and to Antonio J G Ramos and Josep Coca for their support and thoughtful comments during the study of the bloom. Pictures from Fig. 1 were provided by Rogelio Herrera. This is a contribution of the Canarian Observatory of Harmful Algae (OC-HABs).
The authors declare no competing interests.
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Benavides, M., Arístegui, J. Untreated sewage outfalls do not promote Trichodesmium blooms in the coasts of the Canary Islands. Sci Rep 10, 18386 (2020). https://doi.org/10.1038/s41598-020-75447-1