From Marine Protected Areas South Africa website:

After the 2011 National Biodiversity Assessment noted that offshore ecosystems were poorly protected, the Offshore MPA project (2007- 2011) initiated plans to increase protection of offshore ecosystems, which were advanced towards implementation during Operation Phakisa Oceans Economy. A total of 22 new MPAs were gazetted for comment in 2016 as part of a lengthy consultation process. The South African Cabinet granted permission to declare a revised network of 20 new MPAs in October 2018. It took several months to prepare the declaration notices and final regulations. This culminated in the gazetting of 20 new MPAs on 23 May 2019. These take effect on 1 August 2019 and expand the protection of South Africa’s mainland ocean territory to 5%.

From the Operation Phakisa website:

20 new MPAs, and two expanded MPAs were identified through Operation Phakisa‚ a presidential project to fast-track the development of South Africa’s Ocean Economy. The new MPAs will secure protection of marine habitats like reefs‚ mangroves and coastal wetlands which are required to help protect coastal communities from the results of storm surges‚ rising sea-levels and extreme weather. Offshore‚ these MPAs will protect vulnerable habitats and secure spawning grounds for various marine species‚ therefore helping to sustain fisheries and ensure long-term benefits important to food and job security.

From Government Gazette Staatskoerant:

The iSimangaliso Marine Protected Area in KwaZulu-Natal is a coastal and offshore Marine Protected Area stretching from the South Africa-Mozambique border in the north where it extends approximately 34 nautical miles offshore; to Cape St Lucia Lighthouse in the south where it extends approximately 58 nautical miles offshore. 

The purpose for declaring the Marine Protected Area is:

a) To contribute to a national and global representative system of marine protected areas, by providing protection for sites of special sensitivity and sites that are critically endangered; and by providing a large contiguous conservation area which links inshore marine habitats with those further offshore;

b) to contribute to sustainable marine and coastal ecotourism through the zonation for activities which yield socio-economic benefits on the local and national scales;

c) to facilitate fisheries management by protecting spawning stock, allowing stock recovery, and enhancing stock abundance in adjacent areas, in particular, for reef fish and large pelagic fish;

d) for the protection of fauna and flora or a particular species of fauna or flora and the physical features on which they depend, including the canyons which constitute known and potential Coelacanth habitat, vulnerable benthic habitats, including cold water corals and areas which are important migratory corridors for humpback whales and whale sharks and breeding and foraging areas for several turtle species; and

e) to provide reference sites for research, including areas in good ecological condition and areas which may show most clearly the impacts of climate change.

More Information:

Practical Implications of the Draft Regulations to the Management of Marine Protected Areas (25 April 2016) Lexology.com