Spatio-temporal variability of phytoplankton in the southern Benguela upwelling system

Pitcher, GC; Brown, P. C.; Mitchell-Innes, B. A.

doi:10.2989/02577619209504717

Cited by 50 publications

(33 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The large groups observed in the St Helena Bay area may be aggregations associated with surface feeding on schooling fish in a similar manner to that observed in Argentina (Würsig & Würsig 1980). St Helena Bay is very close to the site of a strong, regular upwelling plume enriching the area (Pitcher et al 1992). Shore based observations in the same area showed that dusky dolphins moved offshore during windy conditions that were likely to cause upwelling (Elwen et al 2009).…”

Section: Discussionmentioning

confidence: 99%

“…No published explanation for these apparent hotspots in hake numbers can be found. However, the southern Benguela Current system is a wind-driven upwelling current system in which changes in bottom topography and longshore wind stress can result in locally enhanced and predictable upwelling cells (Pitcher et al 1992). Two of the strongest upwelling cells in the region occur off the Cape Peninsula and Cape…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Near-shore distribution of Heaviside’s (Cephalorhynchus heavisidii) and dusky dolphins (Lagenorhynchus obscurus) at the southern limit of their range in South Africa

Elwen¹,

Thornton²,

Reeb³

et al. 2010

African Zoology

View full text Add to dashboard Cite

Photo-identification surveys over three years along 390 km of coastline north of Cape Town, revealed that Heaviside's dolphin distribution was consistent between years and higher in areas more exposed to swells and with greater long-term availability of small hake Merluccius capensis (their principal prey). Dusky dolphin sighting rates varied considerably between years, but were generally higher in areas with lower hake availability and sandier shores (mostly straighter coastline). Large groups of 50-200 dusky dolphins were only seen in St Helena Bay, the site of a wind-driven upwelling zone. Heaviside's dolphins were found in shallower, cooler water than dusky dolphins and were more likely to be seen during brighter phases of the moon (when nocturnal light conditions may influence the vertical migration patterns of prey) and in areas of high hake abundance. Near-shore fishing activity was higher in the northern half of the study area and clustered around harbours. Set netting occurred only at Yzerfontein and St Helena Bay, but due to changes in the industry is currently thought to be a low threat to the population. Interactions between Heaviside's and dusky dolphins were usually neutral and sympatry appears to be mediated by differences in overall range and the type and size of prey species taken.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Near-shore distribution of Heaviside’s (Cephalorhynchus heavisidii) and dusky dolphins (Lagenorhynchus obscurus) at the southern limit of their range in South Africa

Elwen¹,

Thornton²,

Reeb³

et al. 2010

African Zoology

View full text Add to dashboard Cite

show abstract

“…Diatoms are particularly adapted to upwelling conditions through high doubling rates and their ability to form resting spores, which sink and are subsequently returned to the surface via upwelling (Pitcher et al, 1992). In the Humboldt Current system, EN reduces the upwelling of nutrient-rich water, which results in a reduction of the larger size fraction of the phytoplankton community (e.g.…”

Section: Introductionmentioning

confidence: 99%

Trophic modeling of the Northern Humboldt Current Ecosystem, Part II: Elucidating ecosystem dynamics from 1995 to 2004 with a focus on the impact of ENSO

Taylor

Tam

Blaskovic

et al. 2008

Progress in Oceanography

View full text Add to dashboard Cite

a b s t r a c tThe Northern Humboldt Current Ecosystem is one of the most productive in the world in terms of fish production. Its location near to the equator permits strong upwelling under relatively low winds, thus creating optimal conditions for the development of plankton communities. These communities ultimately support abundant populations of grazing fish such as the Peruvian anchoveta, Engraulis ringens. The ecosystem is also subject to strong inter-annual environmental variability associated with the El Niño Southern Oscillation (ENSO), which has major effects on nutrient structure, primary production, and higher trophic levels. Here our objective is to model the contributions of several external drivers (i.e. reconstructed phytoplankton changes, fish immigration, and fishing rate) and internal control mechanisms (i.e. predator-prey) to ecosystem dynamics over an ENSO cycle. Steady-state models and timeseries data from the Instituto del Mar del Perú (IMARPE) from 1995 to 2004 provide the base data for simulations conducted with the program Ecopath with Ecosim. In simulations all three external drivers contribute to ecosystem dynamics. Changes in phytoplankton quantity and composition (i.e. contribution of diatoms and dino-and silicoflagellates), as affected by upwelling intensity, were important in dynamics of the El Niño of 1997-98 and the subsequent 3 years. The expansion and immigration of mesopelagic fish populations during El Niño was important for dynamics in following years. Fishing rate changes were the most important of the three external drivers tested, helping to explain observed dynamics throughout the modeled period, and particularly during the post-El Niño period. Internal control settings show a mix of predator-prey control settings; however a ''wasp-waist" control of the ecosystem by small pelagic fish is not supported.

show abstract

“…This area is characterised by high phytoplankton biomass, as identified by remotely sensed chlorophyll data (Pitcher & Weeks 2006), and is particularly susceptible to the development of HABs during the latter half of the upwelling season, when the contribution of dinoflagellates to the phytoplankton community is greatest. The high productivity is a result of: (1) the periodic resupply of nutrients to the euphotic zone through upwelling; (2) the relative stability of the physical environment; and (3) retentive circulation in the region (Pitcher et al 1992). …”

mentioning

confidence: 99%

Contrasting wind patterns and toxigenic phytoplankton in the southern Benguela upwelling system

Fawcett¹,

Pitcher²,

Bernard³

et al. 2007

Mar. Ecol. Prog. Ser.

View full text Add to dashboard Cite

The southern Namaqua shelf of the Benguela upwelling system, downstream of the Cape Columbine upwelling cell, is frequently subjected to a variety of harmful algal bloom (HAB) phenomena. Here, winds dictate most physical processes that are important to the development of HABs. Toxic algal cell concentrations and distributions, in relation to their respective toxin content, are compared over 2 autumn periods in successive years which exhibited clearly different wind patterns and hydrographic responses. During the first study period (15 March to 6 April 2005), several periods of relaxation from upwelling-favourable winds were associated with poleward nearshore currents and increasing levels of stratification. The phytoplankton community was dominated by dinoflagellates, including Dinophysis spp. and Protoceratium reticulatum, responsible for the production of toxins associated with diarrhetic shellfish poisoning and yessotoxins, respectively. In contrast, the subsequent study period (7 to 23 March 2006) was characterised by persistent upwelling-favourable winds, equatorward near-surface currents, and a cooler, moderately mixed water column. The phytoplankton assemblage was co-dominated by Pseudo-nitzschia spp. and Chaetoceros spp.; domoic acid concentrations corresponded closely with cell concentrations of Pseudo-nitzschia spp. Contrasting wind patterns, and their influence on water column structure and mesoscale circulation, led to predictably different assemblages of phytoplankton life-forms and their associated toxins.KEY WORDS: Southern Benguela · Upwelling · Harmful algal bloom · Diatom · Dinoflagellate · Algal toxins 348: 19-31, 2007 upwelling in the southern Benguela is highly seasonal due to shifts in the position of the South Atlantic High; the upwelling season extends from September to March, with upwelling reaching a maximum in the austral spring and summer (Nelson & Hutchings 1983). The present study focuses on the greater St. Helena Bay region, where the shelf broadens downstream of the Cape Columbine upwelling cell at 33°S (Fig. 1). This area is characterised by high phytoplankton biomass, as identified by remotely sensed chlorophyll data (Pitcher & Weeks 2006), and is particularly susceptible to the development of HABs during the latter half of the upwelling season, when the contribution of dinoflagellates to the phytoplankton community is greatest. The high productivity is a result of: (1) the periodic resupply of nutrients to the euphotic zone through upwelling; (2) the relative stability of the physical environment; and (3) retentive circulation in the region (Pitcher et al. 1992). Resale or republication not permitted without written consent of the publisherMar Ecol Prog SerA conceptual model of red tide formation in St. Helena Bay has been presented by Pitcher & Nelson (2006). During upwelling, northward flow dominates and an equatorward coastal jet forms off Cape Columbine, where the shelf is narrow and steep (Nelson & Hutchings 1983). Under these conditions, a plume of cold water...

show abstract

Spatio-temporal variability of phytoplankton in the southern Benguela upwelling system

Cited by 50 publications

References 0 publications

Near-shore distribution of Heaviside’s (Cephalorhynchus heavisidii) and dusky dolphins (Lagenorhynchus obscurus) at the southern limit of their range in South Africa

Near-shore distribution of Heaviside’s (Cephalorhynchus heavisidii) and dusky dolphins (Lagenorhynchus obscurus) at the southern limit of their range in South Africa

Trophic modeling of the Northern Humboldt Current Ecosystem, Part II: Elucidating ecosystem dynamics from 1995 to 2004 with a focus on the impact of ENSO

Contrasting wind patterns and toxigenic phytoplankton in the southern Benguela upwelling system

Contact Info

Product

Resources

About