The following are sections from Ugu Lwethu - Our Coast (Goble et al., 2014). Contributions are from a range of authors all of whom are credited per section.
Ecosystems are defined as groups of living organisms (animals, plants and microbes) interacting together and with the non-living components of their environment (air, water and minerals). Coastal and marine ecosystems encompass a wide range of habitat types, providing an integral link between terrestrial and aquatic environments.
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.
Dry 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.
Photo: Fiona MacKay
Photo: Ronel Nel
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.
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 generic global definition of an estuary.
South Africa has two sets of coastal lakes; a group of five in the Southern Cape and a northern series of 8 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.
Photo: Bruce Mann
Given that the coast of KZN provides a gateway to the world, a playground for leisure, and a primary zone for economic development, it is not surprising that there is a high demand for coastal resources and economic development opportunities. This is matched by growing resident and seasonal populations who utilise the coast and supporting infrastructure and services. Collectively these features create a basis for development that is pivotal to the future economy of KZN.
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.
Photo: Judy Mann
Photo: Camilla Floros
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, one of the largest rivers in the country.
Coastal and Marine Ecosystems PDF