Wild Wetlands: the importance of wetlands and the conservation of the St. Lucia estuary

It’s World Wetlands Day and we’re going to explore these incredible ecosystems that provide a plethora of benefits to the environment, to communities and even to sharks! Did you know that wetlands are one of the most productive ecosystems? In fact, 40% of all species rely on wetlands despite them covering less than 1% of the world’s surface. They provide habitat for fish and other wildlife, protect and improve water quality by filtering potentially harmful compounds, store flood waters, act as buffers against the sea, and play their part with atmospheric maintenance by storing carbon in plants and soil – is there anything they can’t do?

Now we want to zoom in a little bit on a specific type of wetland – an estuary. This is the transition zone where a river meets the sea. One of the main ecological roles that estuaries play is to provide nursery habitats to various marine animals. The shallow waters and shelters in amongst vegetation provide the ideal safe habitat for juvenile fish to grow big in. Even sharks and rays make use of these habitats! Species like bull sharks, lemon sharks and mangrove stingrays are known to rely on estuaries for nurseries.

A juvenile mangrove stingray using shallow, protected waters. Video: Chantel Elston

Let’s further zoom in on a local example of a wetland ecosystem– the St. Lucia estuary in the iSimangaliso Wetland Park in KwaZulu-Natal. This estuarine lake system, the largest in Southern Africa and covering an area of 350km2, represents 60% of the estuarine area in the country and has historically been the most important nursery ground for juvenile marine fish along the east coast of South Africa. There have been 155 fish species recorded in the Lake St. Lucia estuarine system, 71 of which use the lake as a nursery area (including the bull shark).

St. Lucia estuary mouth (when the mouth was open). Photo: Lidiko Lodge

Unfortunately, farming around the uMfolozi River since the ‘50s has given rise to significant changes to the estuary system. This has included the removal of swamp vegetation and transforming part of the river into a canal. Then almost a decade ago, an increase in sediments caused the mouth of the estuary to close, meaning that the lake was no longer connected to the sea, and it could no longer function as a critical nursery to the many marine species that relied upon it.

St. Lucia estuary mouth (with the mouth closed). Photo: South Africa Safari Blog

Through the years there have been calls to bulldoze the river mouth with suggestions that, unless the mouth is breached, tourism, industry and the ecosystem will suffer. However, some scientists urged patience for the natural estuarine process to take its course for the long-term health of the estuary. Despite the controversy, it was decided in late 2020, after a multi-disciplinary and multi-sector stakeholder engagement, that the system needed a ‘nudge’ to support the natural processes. As a result, bulldozers rolled in between 4th – 6th January 2021 and the St. Lucia estuary was successfully connected to the sea after 8 years.

Whilst some believe this has set the system back in terms of restoration, others believe this will help reinstate the functionality of the estuary and to bring back the nursery grounds for a number of marine fish. Whichever side of the fence you fall on, one cannot deny the immediate changes this action brought about. In fact, within days of the estuary being reconnected with the sea, bull shark pups were spotted at the mouth. These shark pups would have been born around the time the mouth was opened and would have moved in an out of the estuary mouth, seeking a good nursery habitat. Scientist Ryan Daly even captured the image of a lifetime – a Nile crocodile attacking a bull shark pup! He captioned it ‘when a predator becomes prey’.

Unfortunately, Lake St. Lucia is just one case study among many. Estuaries and wetlands face increasing pressures from us. Human-induced modifications to wetland systems are only too common, and these problems are being exacerbated by global crises such as climate change. It is our responsibility to restore these incredible ecosystems which provide so many benefits to not only us, but countless other species.