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

Carrasco, Nicola K.; Perissinotto, Renzo; Pillay, Deena

doi:10.3354/meps08355

Cited by 50 publications

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“…However, as a result of rising salinity, many species have been eliminated from large areas of the lake, and elsewhere only the most resistant eukaryotes appear to survive (9,37,39,40). Results also suggest that under hypersaline conditions, trophic systems begin to be truncated, as grazers are particularly susceptible to rising salinity, and that microalgal biomass, both benthic and planktonic, initially rises as a result (37).…”

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confidence: 77%

“…Results also suggest that under hypersaline conditions, trophic systems begin to be truncated, as grazers are particularly susceptible to rising salinity, and that microalgal biomass, both benthic and planktonic, initially rises as a result (37). Above 140 on the salinity scale, however, only prokaryotes appear able to survive, and eukaryotes are eliminated from both the plankton and benthos (9).…”

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confidence: 87%

“…The current 10-year-long drought is one of the longest on record, however, and has produced profound changes in the ecological conditions of the lake (4,9,20,37,39,40,52). Since 1992 the mouth has opened to the Indian Ocean on only two occasions: briefly in January 2004 and then for a 6-month period in 2007, when waves generated by Cyclone Gamede, combined with high equinoctial spring tides, breached the berm from the ocean side (9). This infrequent opening of the estuary mouth, coupled with very low freshwater inflow, has resulted in low water levels throughout the system and progressively rising salinities, particularly in the shallow North Lake and False Bay, where high insolation rates, shallow water levels, and high temperatures result in rapid evaporation (58).…”

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confidence: 99%

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Persistent Phytoplankton Bloom in Lake St. Lucia (iSimangaliso Wetland Park, South Africa) Caused by a Cyanobacterium Closely Associated with the Genus Cyanothece (Synechococcaceae, Chroococcales)

Muir

Perissinotto

2011

Appl Environ Microbiol

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, is the largest estuarine lake in Africa. Extensive use and manipulation of the rivers flowing into it have reduced freshwater inflow, and the lake has also been subject to a drought of 10 years. For much of this time, the estuary has been closed to the Indian Ocean, and salinities have progressively risen throughout the system, impacting the biotic components of the ecosystem, reducing zooplankton and macrobenthic biomass and diversity in particular. In June 2009, a bloom of a red/orange planktonic microorganism was noted throughout the upper reaches of Lake St. Lucia. The bloom persisted for at least 18 months, making it the longest such bloom on record. The causative organism was characterized by light and electron microscopy and by 16S rRNA sequencing and was shown to be a large, unicellular cyanobacterium most strongly associated with the genus Cyanothece. The extent and persistence of the bloom appears to be unique to Lake St. Lucia, and it is suggested that the organism's resistance to high temperatures, to intense insolation, and to hypersalinity as well as the absence of grazing pressure by salinity-sensitive zooplankton all contributed to its persistence as a bloom organism until a freshwater influx, due to exceptionally heavy summer rains in 2011, reduced the salinity for a sufficient length of time to produce a crash in the cyanobacterium population as a complex, low-salinity biota redeveloped.

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confidence: 77%

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confidence: 87%

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confidence: 99%

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Persistent Phytoplankton Bloom in Lake St. Lucia (iSimangaliso Wetland Park, South Africa) Caused by a Cyanobacterium Closely Associated with the Genus Cyanothece (Synechococcaceae, Chroococcales)

Muir

Perissinotto

2011

Appl Environ Microbiol

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“…After this initial phase of wide spatial cover, it was decided, on the basis of similarity analysis, that 1 station located on each side of the 3 lakes (False Bay, North Lake, South Lake) and another 2 each for the Narrows and Mouth included most of the spatial diversity observed (Pillay & Perissinotto 2008, Carrasco et al 2010. Hence, from February 2006 until August 2007, 5 representative stations were sampled, viz.…”

Section: Methodsmentioning

confidence: 99%

Microalgal biomass in the St Lucia Estuary during the 2004 to 2007 drought period

Perissinotto

Pillay²,

Bate³

2010

Mar. Ecol. Prog. Ser.

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Phytoplankton and microphytobenthic biomass were investigated over a 4 yr period in the drought-stricken St Lucia Estuary, KwaZulu-Natal, South Africa. This is the largest estuarine lake in Africa and part of the iSimangaliso Wetlands Park, South Africa's first World Heritage Site and a Ramsar Wetland of International Importance. The present study aimed at identifying the factors controlling the extreme variability in its ecological functioning. Water-column chlorophyll a (chl a) concentrations averaged (± SD) 32.3 ± 53.4 mg m -3

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“…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.…”

Section: Abstract: Stable Isotopes · South Africa · Isimangaliso Wetmentioning

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

Abstract: ), while previously dominant zooplankton grazers virtually disappeared. These findings emphasize the complexity of the system and stress the need for further research into the potential impacts of environmental and climate changes on this key African estuarine lake.

Cited by 50 publications

References 44 publications

Persistent Phytoplankton Bloom in Lake St. Lucia (iSimangaliso Wetland Park, South Africa) Caused by a Cyanobacterium Closely Associated with the Genus Cyanothece (Synechococcaceae, Chroococcales)

Persistent Phytoplankton Bloom in Lake St. Lucia (iSimangaliso Wetland Park, South Africa) Caused by a Cyanobacterium Closely Associated with the Genus Cyanothece (Synechococcaceae, Chroococcales)

Microalgal biomass in the St Lucia Estuary during the 2004 to 2007 drought period

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

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