Lake St. Lucia is the largest estuarine lake in South Africa and is a UNESCO World Heritage Site. The St. Lucia
Estuary resides in a poor state due to drought and human impacts which have resulted in the closure of the
mouth to the sea since 2002 and changes in freshwater inflow particularly from theMfolozi River. This provides
a unique opportunity to study the responses of the mangroves that usually grow in an intertidal environment.
High water levels and inundation caused mangroves to die in The Narrows in 2013/2014 which caused concern.
The aim of this study was to investigate the response of the mangroves to fluctuating environmental conditions.
Thiswas done by measuring the population structure and sediment characteristics at four sites in 2010, 2013 and
2014. The reconnection of the Mfolozi River to St. Lucia in 2013 via the Beach Canal and Back Channel as well as
good rains led to an increase inwater levelwhich caused permanent inundation of pneumatophores (aerial roots
of thewhite mangrove Avicennia marina) and anoxic conditions resulting in the mortality of mangroves fringing
the main estuary channel (Site 3 on The Narrows). Self-thinning is a natural process that has occurred at Sites 1
and 2 while Site 4, which was previously considered a dying population, had a recruitment of a new seedling
cohort in 2014. The dieback of mangroves along the water's edge is part of the natural dynamics because
this would have occurred under the natural state for this system when the mouth closed to the sea, water
level was high and the estuary was fresher. This study has shown that site-specific differences will allow for
recruitment and overall survival of mangroves at St. Lucia Estuary