Chemotaxonomic investigation of phytoplankton in the shelf ecosystem of the KwaZulu-Natal Bight, South Africa

Barlow, Raymond G; Lamont, Tarron; Gibberd, M-J; Berg, Marcel van den; Britz, K.

doi:10.2989/1814232x.2015.1106976

Cited by 12 publications

(12 citation statements)

References 28 publications

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“…Early studies showed Chla concentrations in Delagoa Bight ranging between 0.6 and 1.26 mg m -3 (Mordasova, 1980), and more recent investigations (Barlow et al 2008;Kyewalyanga et al, 2007;Sá et al, 2013) have illustrated variable phytoplankton distributions in response to changing circulation patterns (Lamont et al, 2010). On the KZN shelf, a wide range of in situ Chla concentrations has been observed (Barlow et al, 2008(Barlow et al, , 2010(Barlow et al, , 2013(Barlow et al, , 2015Burchall, 1968 a, b;Carter and Schleyer, 1988). Although the variance associated with these Chla values is high (Carter and Schleyer, 1988), in response to rapid changes in hydrographic conditions (Lamont and Barlow, 2015;Lamont et al, 2016;Lutjeharms et al, 2000), there was an indication of maximum phytoplankton biomass occurring during autumn and late winter/early spring (Burchall 1968a, b;Carter and Schleyer, 1988).…”

Section: East Coast Of Southern Africa and Madagascarmentioning

confidence: 99%

Seasonal variation in remotely-sensed phytoplankton size structure around southern Africa

Lamont

Brewin

Barlow

2018

Remote Sensing of Environment

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The three-component model of Brewin et al. (2010) computes fractional contributions of three phytoplankton size classes (micro-(> 20 m), nano-(2-20 m), picophytoplankton (< 2 m)) to the overall chlorophyll a concentration (Chla). Using in situ pigment data, model coefficients were adjusted for application to the southern African marine region. The refined model was applied to seasonal and monthly climatologies of MODIS Aqua Chla around Southern Africa. Chla > 1 mg m-3 was limited to shelf regions along the coasts of Southern Africa and Madagascar, while values < 0.1 mg-3 were found over most of the open ocean between the equator and 38 °S during austral summer and autumn. In winter and spring, low values (< 0.1 mg m-3) were restricted to smaller regions within subtropical gyres, while values up to 0.7 mg m-3 extended over a much greater area of the open ocean. Shelf regions in the northern (NB) and southern Benguela (SB), Agulhas Bank (AB), Agulhas region (AR), and Mozambique Channel (MC) all showed similar seasonal cycles of size structure. On average, micro-phytoplankton comprised > 50 % of the total Chla in these regions with little change throughout the year. The AR shelf differed, with picophytoplankton dominating in summer, and micro-and nanophytoplankton the rest of the year. In the open ocean domains of the NB, SB, and AB regions, nanophytoplankton dominated for most of the year, with picophytoplankton being more prevalent during summer and autumn. In contrast, in the AR open ocean, nanophytoplankton were dominant only during winter and early spring, whereas picophytoplankton dominated throughout the year in the MC open ocean. The refined model characterised previously unknown spatial and temporal changes in size structure in various ecosystems around Southern Africa.

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Section: East Coast Of Southern Africa and Madagascarmentioning

confidence: 99%

Seasonal variation in remotely-sensed phytoplankton size structure around southern Africa

Lamont

Brewin

Barlow

2018

Remote Sensing of Environment

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“…Some of the highest surface chlorophyll concentrations are observed over the Agulhas Bank near the coast between Cape Agulhas and Algoa Bay (Figures 20, 21b, and 22;Probyn, 1994;Demarcq et al, 2003), between Algoa Bay and Port Alfred (Barlow et al, 2010;O'Donoghue et al, 2010) and in the KZN Bight north of Durban (Lamont and Barlow, 2015). Coastal diatom species are the primary contributor to the elevated phytoplankton biomass and primary production observed in these upwelling centers (Carter and Schleyer, 1988;Lamont and Barlow, 2015), with Prochlorococcus and Synechococcus dominant in the offshore regions (Barlow et al, 2015). A subsurface chlorophyll maximum is also observed to form over the shelf in the KZN Bight (Barlow et al, 2015) and in the central Agulhas Bank ( Figure 22) when nutrient concentrations near the surface become limiting (Shannon et al, 1984;Probyn et al, 1995).…”

Section: Impacts On Primary Productionmentioning

confidence: 96%

“…Coastal diatom species are the primary contributor to the elevated phytoplankton biomass and primary production observed in these upwelling centers (Carter and Schleyer, 1988;Lamont and Barlow, 2015), with Prochlorococcus and Synechococcus dominant in the offshore regions (Barlow et al, 2015). A subsurface chlorophyll maximum is also observed to form over the shelf in the KZN Bight (Barlow et al, 2015) and in the central Agulhas Bank ( Figure 22) when nutrient concentrations near the surface become limiting (Shannon et al, 1984;Probyn et al, 1995).…”

Section: Impacts On Primary Productionmentioning

confidence: 99%

“…The concentrations, distribution and movement of nutrients over the southeast African shelf can be strongly influenced by the Agulhas Current via topographically forced upwelling at specific locations (e.g., the St. Lucia upwelling cell in the KZN Bight;Meyer et al, 2002). In general, inorganic nutrient concentrations (nitrate, silicate and phosphate) off southeastern Africa decline in the surface waters from the inner shelf to the outer shelf and into the Agulhas current (Carter and d'Aubrey, 1988;Barlow et al, 2015). However, the interaction of upwelling, with horizontal advection and mixing can…”

Section: Impacts On Primary Productionmentioning

confidence: 99%

“…give rise to complex nutrient distribution patterns in the coastal zone (Meyer et al, 2002;Barlow et al 2015). Nutrient concentrations measured in the near-surface waters (10 m depth) over the shelf in the vicinity of the KZN Bight reveal enrichment of both phosphorus and silicate relative to nitrate compared to Redfield (Carter and d'Aubrey, 1988;Meyer et al, 2002;Barlow et al, 2015) suggesting the potential for nitrate limitation.…”

Section: Impacts On Primary Productionmentioning

confidence: 99%

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Biogeochemical and ecological impacts of boundary currents in the Indian Ocean

Hood

Beckley

Wiggert

2017

Progress in Oceanography

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Monsoon forcing and the unique geomorphology of the Indian Ocean basin result in complex boundary currents, which are unique in many respects. In the northern Indian Ocean, several boundary current systems reverse seasonally. For example, upwelling coincident with northward-flowing currents along the coast of Oman during the Southwest Monsoon gives rise to high productivity which also alters nutrient stoichiometry and therefore, the species composition of the resulting phytoplankton blooms. During the Northeast Monsoon most of the northern Indian Ocean boundary currents reverse and favor downwelling. Higher trophic level species have evolved behavioral responses to these seasonally changing conditions. Examples from the western Arabian Sea include vertical feeding migrations of a copepod (Calanoides carinatus) and the reproductive cycle of a large pelagic fish (Scomberomorus commerson). The impacts of these seasonal current reversals and changes in upwelling and downwelling circulations are also manifested in West Indian coastal waters, where they influence dissolved oxygen concentrations and have been implicated in massive fish kills. The winds and boundary currents reverse seasonally in the Bay of Bengal, though the associated changes in upwelling and productivity are less pronounced. Nonetheless, their effects are observed on the East Indian shelf as, for example, seasonal changes in copepod abundance and zooplankton community structure. In contrast, south of Sri Lanka seasonal reversals in the boundary currents are associated with dramatic changes in the intensity of coastal upwelling, chlorophyll concentration, and catch per unit effort of fishes. Off the coast of Java, monsoon-driven changes in the currents and upwelling strongly impact chlorophyll concentrations, seasonal vertical migrations of zooplankton, and sardine catch in Bali Strait. In the southern hemisphere the Leeuwin is a downwelling-favorable current that flows southward along western Australia, though local wind forcing can lead to transient near shore current reversals and localized coastal upwelling. The poleward direction of this

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