Lake St Lucia, Africa’s largest estuarine lake in crisis: Combined effects of mouth closure, low levels and hypersalinity
Keywords:
drought, estuary, fish, low lake levels, macrobenthic invertebrates, zooplankton
Abstract
The Lake St Lucia estuarine system is the most important nursery ground for juvenile marine fish and prawns along the KwaZulu-Natal coast. The estuary mouth closed in June 2002 because of drought and remained so for 4 years and 9 months. A study to determine the impacts of extended mouth closure, hypersalinity and low lake levels on the mesozooplankton, macrobenthic invertebrates and fish fauna was initiated in 2004. Zooplankton and benthic invertebrate diversity declined, benthic invertebrate community composition changed and the diversity and abundance of fish decreased between 2004 and 2007. In the case of fish, the declines were related to die-offs in the lake and the failed recruitment of post-larvae and juveniles from the marine environment as a result of the mouth having been closed. Options for management intervention under closed-mouth conditions are limited at this time, particularly in the short term, to breaching the mouth and facilitating the inflow of sea water. In the medium term, as was the historical situation, the reconnection of the Mfolozi system to St Lucia should be viewed as a major priority.References
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29. Turpie JK, Adams JB, Joubert J, et al. Assessment of the conservation priority status of South African estuaries for use in management and water allocation. Water SA. 2002;28(2):191–206.
30. Cyrus DP, Jerling HL, Owen RK, Vivier L. Ecological impacts of a short-term diversion of the uMfolozi/uMsunduzi Estuary into Lake St Lucia. CRUZ Investigational Report. 2008;123:1–14.
2. Whitfield AK, Taylor R. A review of the importance of freshwater inflow to the future conservation of Lake St Lucia. Aquatic Conservation: Marine and Freshwater Ecosystems. 2009;19:838–848. doi:10.1002/aqc.1061
3. Taylor RH. Patterns of physical variability in the St Lucia Estuary. Paper 1. In: Ecological responses to changes in the physical environment of the St Lucia estuary. Norwegian University of Life Sciences. Doctor scientarium thesis. 2006;7:1−41.
4. Day JH, Millard NAH, Broekhuysen GJ. The ecology of South African estuaries. Part V: The St Lucia system. Trans R Soc S Afr. 1954;34;129–156. doi:10.1080/00359195409518982
5. Blaber SJM. Fish communities of south-east African coastal lakes. In: Leveque C, Bruton MN, Ssentongo GW, editors. Biology and ecology of African freshwater fishes. Paris: Orstom, 1988; p. 351–362.
6. Day J. Summaries of current knowledge of 43 estuaries in southern Africa. In: Day JH, editor. Estuarine ecology with particular reference to southern Africa. Cape Town: Belkama, 1981; p. 251–330.
7. Taylor RH. Biological responses to changing salinity. In: Taylor RH, editor. Proceedings of the workshop on water requirements for Lake St Lucia. Pretoria: Department of Environment Affairs, 1993; p. 1–83.
8. Jerling HL, Wooldridge TH. Plankton distribution and abundance in the Sundays River estuary, South Africa, with comments on potential feeding interactions. S Afr J Mar Sci. 1995;15:169–184.
9. PRIMER. Version 6. Ivybridge: Primer Enterprisers.
10. Clarke KR, Warwick RM. Change in marine communities: An approach to statistical analysis and interpretation. Plymouth: Plymouth Marine Laboratory, 1994; p. 144.
11. Grindley JR. The vertical migration behaviour of estuarine plankton. Zool Afr. 1972;7:13–20.
12. Champalbert G, Pagano M, Sene P, Corbin D. Relationships between meso- and macro-zooplankton communities and hydrology in the Senegal River Estuary. Estuar Coast Shelf Sci. 2007;74:381–394. doi:10.1016/j.ecss.2007.04.023
13. Whitfield AK. An estuary-association classification for the fishes of southern Africa. S Afr J Sci. 1994;90:411–417.
14. Whitfield AK. Biology and ecology of fishes in southern African estuaries. Ichthyological. Monographs of the J.L.B. Smith Institute of Ichthyology. 1998;(2):1–223.
15. Grindley JR. The role of zooplankton in the St Lucia system. In: Taylor RH, editor. St Lucia research review. Pietermaritzburg: Ezemvelo KZN Wildlife, 1982; p. 88–107.
16. Jerling HL. The zooplankton community of the Mhlathuze (Richards Bay) estuary: Two decades after construction of the harbour. Afr J Mar Sci. 2003;25:289–299. doi:10.2989/18142320309504018
17. Jerling HL. The zooplankton community of Richards Bay Harbour and adjacent Mhlathuze Estuary, South Africa. Afr J Mar Sci. 2008;30:55–62. doi:10.2989/AJMS.2008.30.1.6.456
18. Jerling HL, Weerts S. Mesozooplankton community structure of the Kosi Bay Lake system. Paper presented at: Joint SASAQS/PSSA Conference; 2006 Jun 19–22; Maputo, Mozambique.
19. Pillay D, Perissinotto R. The benthic macrofauna of the St Lucia Estuary during the 2005 drought year. Estuar Coast Shelf Sci. 2008;77:35–46. doi:10.1016/j.ecss.2007.09.004
20. Millard NAH, Broekhuysen GJ. The ecology of South African estuaries. Part X: St Lucia: A second report. Zool Afr. 1970;5:277–307.
21. Boltt RE. The benthos of some southern African lakes. Part V: The recovery of the benthic fauna of St Lucia Lake following a period of excessively high salinity. Trans R Soc S Afr. 1975;41:295–323. doi:10.1080/00359197509519445
22. Reavell PE, Cyrus DP. Preliminary observations on the macrocrustacea of coastal lakes in the vicinity of Richards Bay, Zululand, South Africa. S Afr J Aquat Sci. 1989;15:103–128.
23. Santos SL, Simon JL. Responses of soft-bottom benthos to annual catastrophic disturbance in a South Florida estuary. Mar Ecol: Prog Ser. 1980;3:347–355. doi:10.3354/meps003347
24. Grassle JF, Grassle JP. Opportunistic life histories and genetic systems in marine benthic polychaetes. Mar Res. 1974;32:253–284.
25. Nair KKC, Gopalakrishnan TC, Venugopal P, Peter MG, Jayalakshmi KV, Rao TSS. Population dynamics of estuarine amphipods in Cochin backwaters. Mar Ecol: Prog Ser. 1983;10:289–295. doi:10.3354/meps010289
26. Whitfield AK, Taylor RH, Fox C, Cyrus DP. Fishes and salinities in the St Lucia system – a review. Rev Fish Biol Fish. 2006;16:1–20. doi:10.1007/s11160-006-0003-x
27. Cyrus DP, Vivier L. Status of the estuarine fish fauna in the St Lucia estuarine system, South Africa, after 30 months of mouth closure. Afr J Aquat Sci. 2006;31(1):71–81. doi:10.2989/16085910609503873
28. Mann BQ, Pradervand P. Declining catch per unit effort of an estuarine-dependent fish, Rhabdosargus sarba (Teleostei: Sparidae), in the marine environment following closure of the St Lucia Estuarine System, South Africa. Afr J Aquat Sci. 2007;32:133–138. doi:10.2989/AJAS.2007.32.2.4.201
29. Turpie JK, Adams JB, Joubert J, et al. Assessment of the conservation priority status of South African estuaries for use in management and water allocation. Water SA. 2002;28(2):191–206.
30. Cyrus DP, Jerling HL, Owen RK, Vivier L. Ecological impacts of a short-term diversion of the uMfolozi/uMsunduzi Estuary into Lake St Lucia. CRUZ Investigational Report. 2008;123:1–14.