Inter-Research > MEPS > v379 > p91-107  

MEPS 379:91-107 (2009)  -  DOI: https://doi.org/10.3354/meps07898

Nitrogen nutrition in assemblages dominated by Pseudo-nitzschia spp., Alexandrium catenella and Dinophysis acuminata off the west coast of South Africa

S. Seeyave1,*, T. A. Probyn2, G. C. Pitcher2, M. I. Lucas3, D. A. Purdie1

1National Oceanography Centre, University of Southampton, European Way, Southampton SO14 3ZH, UK
2Marine & Coastal Management, Private Bag X2, Rogge Bay 8012, Cape Town, South Africa
3Zoology Department, University of Cape Town, Rondebosch 7701, South Africa

ABSTRACT: A study was carried out in the southern Benguela upwelling system in 2006 and 2007 to establish how the nutrient regime determines community succession and the selection of harmful algal bloom species. In March 2006, Pseudo-nitzschia spp. reached concentrations of 13 × 106 cells l–1, representing 80% of the total estimated phytoplankton biomass, while chlorophyll a (chl a) reached 57 µg l–1. High rates of NO3 uptake (ρNO3, maximum 0.56 µmol N l–1 h–1) led to NO3 depletion (<0.1 µM). However, cell numbers remained high for several days, sustained by regenerated nitrogen, with ƒ-ratios dropping from 0.79 to 0.12. In March 2007, a bloom of Alexandrium catenella (4.5 × 105 cells l–1, 77% of the phytoplankton biomass) occurred, with surface chl a concentrations of 26 µg l–1. NO3 concentrations were high (10 to 17 µM), sustaining high ρNO3 (maximum 0.61 µmol N l–1 h–1) and ƒ-ratios up to 0.87. In April, Dinophysis acuminata reached 3.1 × 104 cells l–1 (91% phytoplankton biomass), with NO3 concentrations <0.5 µM and ƒ-ratios <0.1, indicative of regenerated production. Nutrient uptake kinetics showed that Pseudo-nitzschia spp. displayed the highest maximum specific uptake rates (15.0 × 10–3 and 18.0 × 10–3 h–1 for NO3 and NH4+, respectively). D. acuminata displayed the highest affinity for NH4+, as shown by its higher α (slope of the nutrient uptake vs. concentration curve) of 20.7 × 10–3, compared to 13.4 × 10–3 and 5.9 × 10–3 h–1 (µmol N l–1)–1 for Pseudo-nitzschia spp. and A. catenella, respectively. D. acuminata was an affinity strategist, successful in nitrogen-depleted waters, whereas both Pseudo-nitzschia spp. and A. catenella were velocity strategists, better adapted to utilising high NO3 concentrations during upwelling pulses.


KEY WORDS: Benguela upwelling system · Harmful algal blooms · Nutrient uptake · Nutrient kinetics   ·   Dinoflagellates   ·   Diatoms


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Cite this article as: Seeyave S, Probyn TA, Pitcher GC, Lucas MI, Purdie DA (2009) Nitrogen nutrition in assemblages dominated by Pseudo-nitzschia spp., Alexandrium catenella and Dinophysis acuminata off the west coast of South Africa. Mar Ecol Prog Ser 379:91-107. https://doi.org/10.3354/meps07898

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