Application of a chlorophyll index derived from satellite data to investigate the variability of phytoplankton in the Benguela ecosystem

Demarcq, Hervé; Barlow, Raymond G; Hutchings, L.

doi:10.2989/ajms.2007.29.2.11.194

Cited by 51 publications

(46 citation statements)

References 19 publications

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“…However, compared with other EBUSs, these investigations have been relatively infrequent and limited in area, and more data are available for the southern than the northern Benguela. In recent years, estimates of phytoplankton biomass and production have become dominated by the use of remotely-sensed ocean colour and modelled output, rather than in situ measurements (Demarcq et al, 2003(Demarcq et al, , 2007Demarcq, 2009;Koné et al, 2005;Weeks et al, 2006).…”

Section: Phytoplankton Biomass and Primary Productionmentioning

confidence: 99%

“…In upwelling regions, maximum chlorophyll concentrations are usually both spatially and temporally coincident with the seasonal maximum in upwelling and are observed downstream of upwelling cells, while the centres of upwelling cells are associated with lower concentrations (Demarcq et al, 2003(Demarcq et al, , 2007Thomas et al, 2001Thomas et al, , 2003Weeks et al, 2006). Phytoplankton biomass is highly variable in the BCLME, with the highest abundances usually found in the nearshore regions (20-80 km from the coast), although elevated chlorophyll a has been observed to extend over 100 km offshore following periods of intense upwelling (Brown et al, 1991;Weeks et al, 2006).…”

Section: Phytoplankton Biomass and Primary Productionmentioning

confidence: 99%

“…Following the method of Demarcq et al (2007), an index of chlorophyll concentration along the west coast of southern Africa was computed by integrating monthly averages of surface chlorophyll a concentration, obtained from satellite sensors, in a zonal direction from the coast to the 1 mg Chl m À 3 offshore level. SeaWiFS data were used from September 1997 to June 2002, and MODIS Aqua data thereafter.…”

Section: Phytoplankton Biomass and Primary Productionmentioning

confidence: 99%

“…In contrast, wind-driven upwelling at discrete upwelling centres in the southern Benguela is strongly pulsed and shows greater seasonal differences, with a narrow band of high plankton productivity in the southern part, restricted to the narrow coastal zone by warm Agulhas water offshore forming a front. North of Cape Columbine, the southern Benguela is characterised by a wider shelf, with elevated biomass and production extending further offshore (Demarcq et al, 2007;Hutchings et al, 2009b).…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Plankton productivity of the Benguela Current Large Marine Ecosystem (BCLME)

Verheye

Lamont

Huggett

et al. 2016

Environmental Development

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Section: Phytoplankton Biomass and Primary Productionmentioning

confidence: 99%

Section: Phytoplankton Biomass and Primary Productionmentioning

confidence: 99%

Section: Phytoplankton Biomass and Primary Productionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Plankton productivity of the Benguela Current Large Marine Ecosystem (BCLME)

Verheye

Lamont

Huggett

et al. 2016

Environmental Development

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“…An increasing trend in measured surface chlorophyll during the 1990s has been documented for the West Coast, based on data from the St Helena Bay region (Verheye 2000), but Hutchings et al (2009) found little overall trend in chlorophyll measurements from 2000 to 2008 in the same region. For the southern Benguela ecosystem as a whole, the phytoplankton variability derived from SeaWiFS ocean colour data and modelled primary production based on depth-integrated chlorophyll a distributions showed no trend over the period 1997 to the early 2000s (Demarcq et al 2007). However, there was an average decrease of 0.4 mg Chl m-3 decade-1 over the continental shelf when the time-series was longer, from 1998 to 2007 (Demarcq 2009), with most of the decrease south of Cape Columbine.…”

Section: Changes In Distribution and Local Abundancementioning

confidence: 97%

Reviewing evidence of marine ecosystem change off South Africa

Moloney

Fennessy

Gibbons

et al. 2013

African Journal of Marine Science

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Recent changes have been observed in South African marine ecosystems. The main pressures on these ecosystems are fishing, climate change, pollution, ocean acidification and mining. The best long-term datasets are for trends in fishing pressures but there are many gaps, especially for non-commercial species. Fishing pressures have varied over time, depending on the species being caught. Little information exists for trends in other anthropogenic pressures. Field observations of environmental variables are limited in time and space. Remotely sensed satellite data have improved spatial and temporal coverage but the time-series are still too short to distinguish long-term trends from interannual and decadal variability. There are indications of recent cooling on the West and South coasts and warming on the East Coast over a period of 20-30 years. Oxygen concentrations on the West Coast have decreased over this period. Observed changes in offshore marine communities include southward and eastward changes in species distributions, changes in abundance of species, and probable alterations in foodweb dynamics. Causes of observed changes are difficult to attribute. Full understanding of marine ecosystem change requires ongoing and effective data collection, management and archiving, and coordination in carrying out ecosystem research.

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Hydrographic variability in the St. Helena Bay region of the southern Benguela ecosystem

Lamont

Hutchings

Berg³

et al. 2015

JGR Oceans

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Cross-shelf distributions of temperature, salinity, water masses, and dissolved oxygen in St. Helena Bay revealed substantial vertical and seasonal variations. In the surface layers, nearshore and offshore temperature and salinity patterns differed, with bay-scale variability linked to upwelling dynamics and coastal processes, while the offshore region was influenced by solar insolation. Spectral analysis revealed that an annual signal prevailed at most stations, and corroborated contrasting patterns between the offshore and nearshore regions, with phase differences suggesting shoreward propagation of the offshore temperature signal. The shelf was dominated by Modified Upwelled Water (MUW) and Subantarctic Mode Water (SAMW), which comprised the primary source of upwelled water. Clear zonation of MUW was evident across the shelf, resulting from seasonal variations in locations of the oceanic and bifurcated shelf-break fronts. Dynamics within St. Helena Bay consistently differed from those further offshore, due to the influences of the shelf-break front, Cape Columbine upwelling plume, and cyclonic recirculation, which appeared to be associated with an intraannual signal with a periodicity of 3-4 months. Persistent hypoxia in the bottom waters suggested the occurrence of a permanent reservoir of Low Oxygen Water (LOW). Seasonal shoreward and offshore expansion of LOW occurred throughout the upwelling season, with maximum extent reached during summer and autumn, due to the coupled effects of advection and local phytoplankton decay. While wind mixing ventilated the water column at nearshore stations in winter, and the onset of upwelling during spring introduced oxygen-richer water from further offshore, hypoxia persisted in the center of the Bay.

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Application of a chlorophyll index derived from satellite data to investigate the variability of phytoplankton in the Benguela ecosystem

Cited by 51 publications

References 19 publications

Plankton productivity of the Benguela Current Large Marine Ecosystem (BCLME)

Plankton productivity of the Benguela Current Large Marine Ecosystem (BCLME)

Reviewing evidence of marine ecosystem change off South Africa

Hydrographic variability in the St. Helena Bay region of the southern Benguela ecosystem

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