Lake St Lucia, Africa’s largest estuarine lake in crisis: Combined effects of mouth closure, low levels and hypersalinity

Cyrus, D. P.; Jerling, H.L.; MacKay, Fiona; Vivier, L

doi:10.4102/sajs.v107i5/6.291

Cited by 6 publications

(7 citation statements)

References 14 publications

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“…The mouth of the St Lucia system closed in 2002 due to below-average rainfall and, except for a six-month open phase in 2007, has since remained closed (Cyrus et al 2011).…”

mentioning

confidence: 99%

Prawn community structure in the subtropical Mfolozi–Msunduzi estuarine system, KwaZulu-Natal, South Africa

Collocott

Vivier

Cyrus

2014

African Journal of Aquatic Science

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The life cycles of many marine and freshwater prawn species are closely associated with estuarine habitat. Here, the prawn community of the Mfolozi-Msunduzi estuarine system is described and the system's potential as an alternative nursery for prawns during prolonged closure of the adjacent St Lucia estuarine system is examined. Sampling was conducted at five localities in summer and winter in 2007-2012. The Mfolozi-Msunduzi Estuary is a river-dominated system with mouth condition, sediment grain size and turbidity being the most important factors affecting the structure of its prawn community. Twelve prawn species were recorded, including five marine penaeid and five freshwater palaemonid species. The prawn community was numerically dominated by freshwater Macrobrachium equidens and two penaeids, Fenneropenaeus indicus and Metapenaeus monoceros. Significant differences were recorded between summer and winter samples, with freshwater species dominating the catch in summer, while penaeid species were dominant in winter. The marked seasonal change in the prawn community was related to strong river flows during summer creating low-salinity conditions, unsuitable for penaeid postlarval development, throughout most of the system. Compared to St Lucia, the Mfolozi-Msunduzi Estuary can be regarded as a poor alternative nursery area for penaeids during the summer peak postlarval recruitment period.

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“…The mouth of the St Lucia system closed in 2002 due to below-average rainfall and, except for a six-month open phase in 2007, has since remained closed (Cyrus et al 2011).…”

mentioning

confidence: 99%

Prawn community structure in the subtropical Mfolozi–Msunduzi estuarine system, KwaZulu-Natal, South Africa

Collocott

Vivier

Cyrus

2014

African Journal of Aquatic Science

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“…Agricultural practices in the catchment and in the immediate vicinity of the estuary have led to an increase in sediment loads in the system, a decrease in the freshwater inflow and a change in the nutrient content of the water. The Mfolozi River, historically a major source of fresh water, was artificially separated from the mouth of the St Lucia estuarine system in 1952, reducing the ability of the St Lucia system to self-regulate the open/ closed state of the mouth (Cyrus et al 2011). The establishment of large timber plantations on the eastern shores also reduced freshwater levels in the system (Perissinotto et al 2013).…”

Section: Discussionmentioning

confidence: 99%

Do sawfishPristisspp. represent South Africa's first local extirpation of marine elasmobranchs in the modern era?

Everett

Cliff

Dudley³

et al. 2015

African Journal of Marine Science

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Largetooth sawfish Pristis pristis and green sawfish P. zijsron were not uncommon in catches made in KwaZulu-Natal (KZN) on the east coast of South Africa in the mid part of the last century but apparently have disappeared from this area. This paper traces the decline in sawfish catches from 1951 and assesses the current population status and local extinction risk, based on historical and current records up to 2012. Records were collected from research surveys, literature, media and museum specimens, and through contacting researchers and conservation managers who have worked in KZN coastal and estuarine areas. A total of 150 green sawfish, 7 largetooth sawfish and 89 unidentified sawfish records were located. Most sawfish (115) were caught during a four-year (1967-1970) gillnetting survey conducted by the Oceanographic Research Institute in the St Lucia estuarine system while 91 were caught in the bather protection nets installed and maintained along the KZN coast by the KwaZulu-Natal Sharks Board. Sawfish ranged from 63 to 533 cm total length (TL). Sawfish caught in the estuarine environments (mean TL 162 cm [SD 72], n = 95) were significantly smaller than those caught in the inshore marine environments (mean TL 310 cm [SD 109], n = 83), confirming the importance of estuaries as pupping and nursery areas. The St Lucia estuarine system, given the high abundance of sawfish, was determined to be the most important nursery area in KZN. The last sawfish encountered in KZN, which was not identified to species level, was caught in the bather protection nets in 1999 and released alive. Extinction probability analysis indicates that sawfish no longer occur in KZN waters. Anthropogenic changes to the St Lucia estuarine system, as well as to other KZN estuaries, gillnetting for bather protection, and illegal fish harvesting, coupled with a non-adaptive life-history style, may have precipitated the disappearance of sawfish from KZN waters.Online supplementary material: The complete list of records and specimens for largetooth sawfish Pristis pristis and green sawfish P. zijsron located by consulting various data sources, primary literature, media, museums and local conservationists and scientists is available online in Supplementary Appendix S1 at http://dx.

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“…The trophic position of fish species at the estuary mouth displayed a general increase compared to that in the hypersaline drought phase ( Hypersaline conditions in Lake St Lucia have had adverse effects on spawning and recruitment of juvenile fish (Cyrus and Vivier 2006), allowing only the most euryhaline species to survive and reproduce (Vivier and Cyrus 2009). This has led to a drastic reduction in the fish diversity of St Lucia, especially under closed-mouth conditions, when estuary-associated marine species were unable to recruit (Cyrus et al 2011). The high rainfall experienced in December 2010-January 2011 led to a substantial decrease in salinity of the system due to increased freshwater input from rivers.…”

mentioning

confidence: 97%

Flood effects on trophic linkages of selected fish species in the littoral zone of the St Lucia estuarine system, South Africa

Peer

Carrasco

Perissinotto

et al. 2013

African Journal of Aquatic Science

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The St Lucia Estuary, a UNESCO World Heritage Site, has experienced prolonged mouth closure since 2002. Until recently it was hypersaline, but heavy rainfall between October 2010 and January 2011 led to a large overall decrease in salinity. A stable isotope study was conducted in March 2011 on selected fish species from the nearshore environments at Charter's Creek and the estuary mouth region to determine the influence of flooding events on their diet. Oreochromis mossambicus, the dominant fish species at both sites, had a generalised diet and occupied the lowest trophic level both before and after flooding. Monodactylus argenteus, Leiognathus equula and Gerres acinaces from the mouth area displayed a largely zooplanktivorous diet and showed some changes in prey species between drought and post-flood conditions.

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Lake St Lucia, Africa’s largest estuarine lake in crisis: Combined effects of mouth closure, low levels and hypersalinity

Cited by 6 publications

References 14 publications

Prawn community structure in the subtropical Mfolozi–Msunduzi estuarine system, KwaZulu-Natal, South Africa

Prawn community structure in the subtropical Mfolozi–Msunduzi estuarine system, KwaZulu-Natal, South Africa

Do sawfishPristisspp. represent South Africa's first local extirpation of marine elasmobranchs in the modern era?

Flood effects on trophic linkages of selected fish species in the littoral zone of the St Lucia estuarine system, South Africa

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