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Productivity of dinoflagellate blooms on the west coast of South Africa, as measured by natural fluorescence
Mitchell-Innes, B.A.; Pitcher, G.C.; Probyn, T.A. (2000). Productivity of dinoflagellate blooms on the west coast of South Africa, as measured by natural fluorescence. S. Afr. J. Mar. Sci./S.-Afr. Tydskr. Seewet. 22: 273-284
In: South African Journal of Marine Science = Suid-Afrikaanse Tydskrif vir Seewetenskap. Marine & Coastal Management: Cape Town. ISSN 0257-7615, more
Peer reviewed article  

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    Chlorophyll; Chlorophyll; Irradiance; Migration; Migration; Migration; Photosynthesis; Populations; Populations; I, Pacific [Marine Regions]; Marine

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  • Mitchell-Innes, B.A.
  • Pitcher, G.C.
  • Probyn, T.A.

    The biomass and productivity of phytoplankton populations inshore on the west coast of South Africa were investigated towards the end of the upwelling season, a period when high-biomass dinoflagellate blooms are common. Productivity was estimated from natural fluorescence measurements (P-NP) using photosynthesis (P) v. irradiance (E) relationships (P-E) and by means of the in situ C-14-method (P-C). A linear regression of P-NF productivity against P-C and P-E productivities yielded a slope of 0.911 and an r(2) of 0.83 (n = 41). Physical and biological variability was high inshore. reflecting alternating periods of upwelling and quiescence. Mean chlorophyll inshore (within a 12 m water column) ranged from 0.7 to 57.8 (mean = 8.9) mg m(-3), mean P-NF productivity ranged from 8.4 to 51.0 (mean = 24.6) mgC.m(-3).h(-1) and daily integral P-NF productivity from 0.8 to 4.8 (mean = 2.3) gC.m(-2) day(-1). Transects sampled during active and relaxation phases of upwelling had different chlorophyll distributions. High chlorophyll concentrations (sometimes > 50 mg.m(-3)) were associated with surface blooms within the region of the upwelling front. Estimates of daily water-column PNF productivity within these frontal blooms ranged from 4.0 to 5.6 gC.m(-2) day(-1). With relaxation of wind stress, blooms dominated by dinoflagellates flooded shorewards and often formed red tides. Chlorophyll concentrations of > 175 mg.m(-3) and productivity rates > 500 mgC(.)m(-3.)h(-1) and 12 gC.m(-2.)day(-1) were measured during a particularly intense red tide. Offshore, the water column was highly stratified with a well-defined subsurface chlorophyll maximum layer within the pycnocline region. Estimates of daily water-column P-NF productivity ranged from 2.4 to 4.0 gC(.)m(-2)day(-1) offshore. The high productivity of shelf waters on the West Coast in late summer can be ascribed largely to dinoflagellate populations and their success in both upwelling systems and stratified conditions.

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