The development and decline of phytoplankton blooms in the southern Benguela upwelling region

Brown, Penelope Cranstoun

The development and decline of phytoplankton blooms in the southern Benguela upwelling region

Thesis / Dissertation

1986

Abstract

[page ii, 27 missing] These "Redfield productivity 14 estimates" were similar to C-uptake productivity but lower than estimates obtained from changes in particle volume. If the period of maximum nutrient decrease was used for the calculations, the "Redfield productivity 14 estimates" lie between the C-uptake and particle volume estimates. 14 Daily rates of C-uptake water column productivity ranged between 0.94 and 14.01 g C.m- 2 .d- 1 (mean 3.80 g C.m- 2 .d- 1) and were similar to or higher than productivity estimates reported for other upwelling areas. Phytoplankton biomass in the upper 50 metres ranged between 8 and 506 mg phll �- m- 2 (mean 208 mg chll �.m- 2); on average, about half the biomass occurred below the 1% light level indicating that self-shading is an important factor limiting primary production in the Benguela upwe!ling system. The temporal scale of phytoplankton bloom development was investigated in terms of changes in chlorophyll � concentrations in the euphotic zone. The build up and decline of the primary phytoplankton (diatom) bloom in newly upwelled water occurred within 6-8 days. The initiation of blooming appears to be controlled by the stability of the water body (vertical and horizontal), and the decline of the bloom was usually associated with reduced nutrient levels and is considered to result mainly from phytoplankton cells sinking out of the surface layers. Dispersive processes may also contribute to bloom decline. Zooplankton grazing made little impact on the phytoplankton community. The wide coastal band of chlorophyll-rich water seen in satellite images to well beyond the outer limit of the drogue tracks, suggests that both regenerated nutrients and new nutrients (entrained into surface waters after the primary bloom), maintain primary production in shelf waters at moderate levels than the 6-8 days suggested by this study.

Keywords

Science

Reference:

Collections

PhD / Doctoral

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