The KZN coastal environment is home to a range of ecosystems that support high diversity and endemic species. These include coastal and aquatic vegetation, sandy and rocky shores, transitional ecosystems such as estuaries, coastal lakes, mangroves and wetlands, and dynamic systems such as sub-tidal reefs and soft substrata.
Arid coastal dune systems are ever changing with storms and seasons. Many of the coastal communities may disappear in a single storm event or gradually change in response to changing environmental factors. The coastal dune communities are often quite distinct, consisting of monospecific stands of pioneer plants. In other cases there may be a graduation from the pioneers into thicket, so that the different communities are not that distinct.
The coastline of KZN is an ocean-exposed, high energy interface between land and sea. Sandy shores comprise a significant proportion of this dynamic boundary, noting that here the term “sandy shores” refers to the coupled and contiguous dune, intertidal beach and surf-zone ecosystems. Encouragingly, a diversity of sandy shores with unique ecological attributes is still well represented in KZN.
Although estuaries are distinct habitats with an individual ecology, they form part of a transition gradient where freshwater from rivers meets saltwater from the sea. In the broadest sense, this is the longest standing and most universally accepted definition of an estuary. KZN has some of South Africa's finest estuaries, which provide a suite of goods and services to the province's communities. However, they are the most vulnerable of ecosystems and many of KZN's smaller estuaries are in a degraded state.
South Africa has two sets of coastal lakes; a group of five lakes located in the Southern Cape, and a northern series of 8 lakes located on the sandy coastal plain north of the Thukela River in KZN. These 13 water bodies differ from the estuaries along this coast in that they lack a surface water connection with the sea under current conditions and are highly variable in their origins and contemporary characteristics.
Mangroves occur on the eastern coastline of South Africa, from East London (Nahoon Estuary) to Kosi Bay, between mean sea level and mean highwater springtide level. They are inundated during high tide and exposed during low tide. Changes in freshwater inflow to estuaries, increased sedimentation due to land degradation and transformation, and prolonged closed mouth conditions all negatively affect mangroves. While the total area of mangroves in KZN has marginally increased in recent times, the geographic distribution of mangroves has unfortunately been reduced.
Wetlands are formally defined by the South African National Water Act and the ICM Act as "land which is transitional between terrestrial and aquatic systems where the watertable is usually at or near the surface, or the land is periodically covered with shallow water, and which in normal circumstances supports a vegetation typically adapted to life in saturated soil.” Historically, wetlands were often seen to be synonymous with wastelands and smelly bogs, marshlands, fens and swamps. As a result, many wetlands were drained, filled in or otherwise destroyed, often in support of “development”. Today wetlands are acknowledged for their value and role in delivering environmental goods and services. Fortunately, KZN is endowed with some excellent wetlands and thanks to
several past scientists and champions of wetlands, several are well protected and valued.
Rocky shores account for about 20% of the coast and are mainly located on the southern and central coast. They are composed of dolerite, granite, as well as Quaternary, Ordovician and Ecca sandstone. North of Cape Vidal, the rocky shores are interspersed between long stretches of sandy beach and are composed of Quaternary sandstone. The main threat to KZN rocky shores is coastal development, and given that they represent an important and highly vulnerable part of the coastal zone, these systems need careful protection to ensure long-term sustainability and productivity.
The subtidal reefs of KZN can be partitioned into two groups: coral reefs and rocky reefs. The coral reefs are located in the northern subtropical region of the province, where the warm climate and clear water have resulted in rich coral growth and abundant marine life. The rocky reefs are scattered intermittently along the rest of the KZN coast, with the most extensive reef structures found south of Durban, approximately 5 km offshore of the Umkomaas River.
Subtidal Soft Sediments
The KZN shelf edge, at 20 m, is a habitat that is always covered by water (subtidal) and characterised by soft sediment at the bottom. Coastal and marine sediments, ranging from large gravel elements to fine muds, occupy over 70% of the seafloor and constitute one of the largest habitats on earth. In KZN the most significant subtidal soft sediment habitat is found on the continental shelf between Richards Bay and Durban. This uncharacteristicly wide shelf section, known as the Natal Bight, has been identified as being highly productive due to the influence of local oceanographic features as well as out-welling via the Thukela River, one of the largest rivers in the country.
ORI • Nelson Mandela Metropolitan University • Rhodes University • University of Ulster • CSIR
EDTEA • ORI
Roy Lubke • Linda Harris • Ronel Nel • Fiona MacKay • Steven Weerts • Andrew Cooper • Janine Adams • Rudy van der Elst • Erika Steyn • Camilla Floros • Candice Untiedt