Research Articles

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

Digby Cyrus, Hendrik Jerling, Fiona MacKay, Leon Vivier
South African Journal of Science | Vol 107, No 3/4 | a291 | DOI: https://doi.org/10.4102/sajs.v107i3/4.291 | © 2011 Digby Cyrus, Hendrik Jerling, Fiona MacKay, Leon Vivier | This work is licensed under CC Attribution 4.0
Submitted: 26 May 2010 | Published: 09 March 2011

About the author(s)

Digby Cyrus, University of Zululand, South Africa
Hendrik Jerling, University of Zululand, South Africa
Fiona MacKay, Oceanographic Research Institute, South Africa
Leon Vivier, University of Zululand, South Africa


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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.

Keywords

drought; estuary; fish; low lake levels; macrobenthic invertebrates; zooplankton

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