Annual cycle of microalgal biomass in a South African temporarily-open estuary: nutrient versus light limitation

Nozais, Christian; Perissinotto, Renzo; Mundree, Sarasvathi

doi:10.3354/meps223039

Cited by 78 publications

(34 citation statements)

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“…Phytoplankton biomass was determined fluorometrically (Turner Designs 10-AU) after cold extracting chl a and phaeopigments from filters in 10 ml 90% acetone for 48 h in the dark. Microphytobenthic cores (internal diameter = 2 cm, n = 3, depth = 1 cm) were collected on each sampling occasion at each station and placed in 100 ml polyethylene bottles containing 30 ml 90% acetone for microphytobenthic chl a extraction (Nozais et al 2001). Biomass was again determined flourometrically and expressed as mg chl a m -2 .…”

Section: Methodsmentioning

confidence: 99%

Zooplankton of the St. Lucia Estuary during the current drought cycle: a comparison between open- and closed-mouth conditions

Carrasco¹,

Perissinotto²,

Pillay³

2010

Mar. Ecol. Prog. Ser.

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Section: Methodsmentioning

confidence: 99%

Zooplankton of the St. Lucia Estuary during the current drought cycle: a comparison between open- and closed-mouth conditions

Carrasco¹,

Perissinotto²,

Pillay³

2010

Mar. Ecol. Prog. Ser.

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“…The total chlorophyll-a (chl-a) concentrations in IOCEs (0.1 and 15.4 mg chl-a.m À3 ) are lower than those reported for permanently open systems (POEs) (20-100 mg chl-a.m À3 ) within the same geographic region [4,12,15] (Table 1) due to reduced macronutrient availability as a result of limited freshwater inflow [12,14,16]. The inflow of freshwater into these systems is characterised by increased phytoplankton biomass likely sustained by the increase in macronutrient availability [12,16].…”

Section: Biologymentioning

confidence: 81%

“…In contrast to the water column, microphytobenthic algae concentrations in IOCEs are two to three orders of magnitude higher than the water column phytoplankton biomass and substantially higher than those recorded in permanently open systems within the same region [4,14,[25][26][27][28]. A combination of low turbidity, high concentrations of macronutrients in the sediments, and reduced current flow contributes to the elevated microphytobenthic algae biomass in IOCEs [4].…”

Section: Biologymentioning

confidence: 99%

“…Following periods of high rainfall (>100 mm in a month) and freshwater runoff, the volume of water in the estuary rises until it exceeds the height of the sandbar [1][2][3]. It is at this stage that breaching usually occurs, with a consequent drastic drop in water level exposing large areas of substratum [2,4]. During the subsequent period, the estuary will be tidally dominated until such time that long-shore drift contributes to the reformation of the sandbar at the mouth of the system.…”

Section: Introductionmentioning

confidence: 99%

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The Ecology and Food Web Dynamics of South African Intermittently Open Estuaries

Froneman¹

2018

Estuary

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This chapter provides an overview of the ecology and food web dynamics of southern African intermittently open/closed estuaries (IOCEs). Intermittently open/closed estuaries experience periodic isolation from the ocean due to a sandbar at the mouth and account for some 71% of all estuaries along the southern African coastline. Field studies indicate that the ecosystem functioning of IOCEs is strongly linked mouth phase (open vs. closed) of these systems. During the closed phase, these systems are generally characterised by low biological diversity and elevated biomass of both invertebrates and vertebrates, which are thought to be sustained by elevated biomass of microphytoplankton and zooplankton within these systems. The low diversity can be related to the virtual absence of marine species within these systems due to the presence of a sandbar at the mouth which limits recruitment. The overflow of marine waters into the estuary during winter storms or spring high tides contributes to the recruit of marine breeding species into these systems. Heavy rainfall in the catchment areas of these systems culminates in the water levels of these systems rising until such time the estuary breaches. The breaching event coincides with the outflow of biologically rich estuarine waters into the marine environment and provides an opportunity for marine breeding species to recruit into these systems. Global warming is likely to contribute to changes in the hydrodynamics of these systems with a concurrent impact on the food webs of these systems.

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“…Phytoplankton biomass was determined fluorometrically (Turner Designs 10-AU) after cold extracting chl a and phaeopigments from filters in 10 ml 90% acetone, for 48 h in the dark. Microphytobenthic cores (2 cm internal diameter, n = 3, depth = 1 cm) were collected at each station and placed in 100 ml polyethylene bottles containing 30 ml 90% acetone for chl a extraction (Nozais et al 2001 To obtain an estimate of SOM, the upper 1 cm layer of sediment was collected and treated with excess 2% hydrochloric acid (HCl) in order to remove carbonates. The sediment was then rinsed thoroughly with distilled water, dried in an oven at 60°C for 24 h, and subsequently crushed with a pestle and mortar (e.g.…”

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confidence: 99%

Spatial and temporal variations in the diet of the mysid Mesopodopsis africana in the St. Lucia Estuary (South Africa)

Carrasco¹,

Perissinotto²

2010

Mar. Ecol. Prog. Ser.

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This study presents one of the few known examples where a mysid species has been observed modifying its diet rapidly and under natural conditions in response to environmental changes. Mesopodopsis africana is a dominant mysid in many estuaries along the east coast of South Africa, and a key species in the St. Lucia Estuary, Africa's largest estuarine lake. St. Lucia is currently undergoing severe desiccation owing to freshwater deprivation. Lack of freshwater input has dampened the effect of temporal variations, while different regions have become more spatially heterogeneous. The mixed model SIAR v 4.0 (stable isotope analysis in R) was used to determine the likely contribution of each of the available carbon sources to the diet of M. africana. The copepod Pseudodiaptomus stuhlmanni made a significant contribution to M. africana's diet in the Mouth region. At Catalina Bay, mysids mostly utilized particulate organic matter (POM), while at Charters Creek they were most closely associated with the macroalga Cladophora sp. The sensitivity of Charters Creek to drought effects is emphasized here, as well as the important role M. africana plays in this habitat as an omnivore, increasing the connectance and, hence, sustaining its food web. While the Mouth and Narrows are partly protected from drought effects, the northern lakes have experienced further increases in salinity during the past decade, forcing the periodical exclusion of this mysid from much of the system. This has lead to severe effects on the food webs that the mysid supports under normal conditions. KEY WORDS: Stable isotopes · South Africa · iSimangaliso Wetland Park · Trophic relations · Key speciesResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 417: 127-138, 2010 ences cyclical wet and dry phases, each lasting between 4 and 10 yr (Begg 1978). Past agricultural practices, combined with the below-average rainfall the area has received since 2002, have resulted in the estuary being cut off from the ocean. Low freshwater input and high evaporation rates have led to the persistence of a reversed salinity gradient, with hypersaline conditions in the upper reaches. These harsh conditions combined with the closed-mouth state, have resulted in only the most adaptive species remaining (Carrasco et al. 2010). Dominant zooplankton within the St. Lucia Estuary include the mysid Mesopodopsis africana and the calanoid copepods Pseudodiaptomus stuhlmanni and Acartia natalensis. While the copepods are numerically dominant, mysids tend to be more important in terms of biomass (Wooldridge 1999). Due to the ongoing drought, M. africana has disappeared from large sections of the estuarine lake, currently occurring only in its mouth region and in parts of the Narrows and South Lake (Fig. 1).The present study examines the implications of harsh environmental conditions on the key zooplankton species Mesopodopsis africana. Knowledge of food web properties, such as trophic processes, enables inferences to be made ab...

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Annual cycle of microalgal biomass in a South African temporarily-open estuary: nutrient versus light limitation

Cited by 78 publications

References 53 publications

Zooplankton of the St. Lucia Estuary during the current drought cycle: a comparison between open- and closed-mouth conditions

Zooplankton of the St. Lucia Estuary during the current drought cycle: a comparison between open- and closed-mouth conditions

The Ecology and Food Web Dynamics of South African Intermittently Open Estuaries

Spatial and temporal variations in the diet of the mysid Mesopodopsis africana in the St. Lucia Estuary (South Africa)

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