Using cell size to represent phytoplankton diversity in studies of nitrogen dynamics in the southern Benguela
type: CreativeWork
description: Phytoplankton are a key component in the functioning of marine ecosystems and play a central role in the cycling of nitrogen and other elements. Metrics that can adequately represent the biogeochemical processes associated with phytoplankton diversity are needed in order to make use of remote sensing and modeling platforms. A single-value size proxy, effective diameter (Deff ), represents the mean volume to surface area ratio across the nano and micro plankton size fraction (2-200µm) in the southern Benguela, but has yet to be tested regarding its biogeochemical relevance. Cell size imposes overarching constraints on phytoplankton metabolism; there are therefore strong grounds for evaluating the usefulness of the metric (Deff ) in studies of nitrogen dynamics in diverse, natural assemblages. Three case studies were used to explore the nitrogen dynamics in naturally occurring assemblages and to evaluate the relationships between Deff and the uptake of the different sources of nitrogen. Two of the case studies comprised high biomass, harmful algal blooms observed off Lamberts Bay during an upwelling/downwelling cycle. The third case study used bi-monthly sampling over a full year in Saldanha Bay. The Lamberts Bay case studies involved blooms occasionally dominated by HAB-forming species: a mixotrophic ciliate, Myrionecta rubra, and a dinoflagellate, Prorocentrum triestinum. The nitrogen uptake rates followed the well observed pattern of high nitrate uptake by large cells and regenerated nitrogen uptake by small cells. Myrionecta rubra had a wide range of nitrate (O₃⁻ ) uptake rates (0.02-0.3 µmol N L⁻¹ h⁻¹). Prorocentrum triestinum showed slower rates of O₃⁻ uptake (0.01-0.2 µmol N L⁻¹ h⁻¹) and dominated in low O₃⁻ , stratified conditions. Diatoms were the most efficient utilisers of O₃⁻ and total nitrogen in these cases. The effective diameter was significantly related to the uptake rates of ammonium (NH₄⁺ ) (r=-0.54, p<0.005) and urea (r=-0.59, p<0.005), but not O₃⁻…
abstract: Phytoplankton are a key component in the functioning of marine ecosystems and play a central role in the cycling of nitrogen and other elements. Metrics that can adequately represent the biogeochemical processes associated with phytoplankton diversity are needed in order to make use of remote sensing and modeling platforms. A single-value size proxy, effective diameter (Deff ), represents the mean volume to surface area ratio across the nano and micro plankton size fraction (2-200µm) in the southern Benguela, but has yet to be tested regarding its biogeochemical relevance. Cell size imposes overarching constraints on phytoplankton metabolism; there are therefore strong grounds for evaluating the usefulness of the metric (Deff ) in studies of nitrogen dynamics in diverse, natural assemblages. Three case studies were used to explore the nitrogen dynamics in naturally occurring assemblages and to evaluate the relationships between Deff and the uptake of the different sources of nitrogen. Two of the case studies comprised high biomass, harmful algal blooms observed off Lamberts Bay during an upwelling/downwelling cycle. The third case study used bi-monthly sampling over a full year in Saldanha Bay. The Lamberts Bay case studies involved blooms occasionally dominated by HAB-forming species: a mixotrophic ciliate, Myrionecta rubra, and a dinoflagellate, Prorocentrum triestinum. The nitrogen uptake rates followed the well observed pattern of high nitrate uptake by large cells and regenerated nitrogen uptake by small cells. Myrionecta rubra had a wide range of nitrate (O₃⁻ ) uptake rates (0.02-0.3 µmol N L⁻¹ h⁻¹). Prorocentrum triestinum showed slower rates of O₃⁻ uptake (0.01-0.2 µmol N L⁻¹ h⁻¹) and dominated in low O₃⁻ , stratified conditions. Diatoms were the most efficient utilisers of O₃⁻ and total nitrogen in these cases. The effective diameter was significantly related to the uptake rates of ammonium (NH₄⁺ ) (r=-0.54, p<0.005) and urea (r=-0.59, p<0.005), but not O₃⁻…
author: Atkins, Josephine ffion
language: eng
date published: 2017
date modified: 2026-07-22T22:23:09Z
provider: University of Cape Town
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Department of Oceanography

PropertyValue
property ID: Handle
value: http://hdl.handle.net/11427/25208