Our Oceans

The Ocean is bigger, deeper, more connected and has more ecosystem types than you may think…

South Africa has three connected oceans and unrolling the blue blanket reveals diverse and vibrant ecosystems

There is one global ocean although five different oceans have been recognised and can be considered as different but connected oceans. South Africa has territory in three of these connected oceans – the Atlantic, the Indian and the Southern Ocean and unrolling the blue blanket of the ocean surface reveals diverse and vibrant ecosystems 

Unrolling the blue blanket means learning about the world beneath the waves. It means finding answers to some of the important questions like…  

How big is the ocean?

How deep is the ocean?

How connected is the ocean?

How many different kinds of ecosystems are there in the ocean?

What are the zones of the ocean?

Why is the ocean around South Africa so unique? 

The ocean is bigger than you might think.

Most of Earth is water, and the Ocean covers 70% of the planet’s surface. It connects far distant continents, countries, cultures and people. Although it may seem as though it is one big blue expanse, the ocean has unique features in different parts of the world. By rolling back the big blue blanket, we can uncover more of the incredible diversity hidden beneath the waves.

The ocean is deeper than you may think

The deepest part of our ocean is about 11 000m deep. That is 11km deep and the height of 11 Table Mountains! Hundreds of thousands of different animals and plants live in many different ecosystems and habitats in a space that size.

The ocean is as deep as 11 Table Mountains stacked on top of one another,

The ocean is an open interconnected system

Everything in the ocean is connected. There are few physical barriers to movement through the ocean; there are no fences, borders, cities and roads separating areas. Mobile animals, larvae and algal spores are able to move across the seascape between ecosystems, habitats and regions. Many animals have long migration routes, travelling thousands of kilometres every year to breed and feed. Even invertebrates (animals without backbones like crabs, starfish, corals  and sponges) may spend long periods travelling across the ocean especially as juveniles (larvae).  Many such animals have multiple juvenile or larval life phases and have extended larval dispersal distances, finally settling in areas where they are best suited.

With the oceans as the main focus, this map (Spilhaus projection) shows that the Pacific, Atlantic, Indian, Arctic and Southern Oceans are all connected.

Many ecosystem types are found in the ocean

It takes a great deal of work for scientists to define an ecosystem type. Defining ecosystem types beneath the vast and inaccessible sea takes even more work than on land. This type of ocean exploration requires  specialised equipment that can function kilometres underwater where water pressure is high; temperature is low and light is absent. 

An ecosystem is an area where the living (plants and animals) and non-living (the physical environment) components interact with each other. Ecosystem types are areas that share the same types of living and non-living components and where the interactions between these components are similar. To define a marine ecosystem type scientists must first research the abiotic (non-living) conditions of an area, for example, whether it is rocky, sandy or muddy, and whether there are any ‘geomorphic features’ like seamounts or canyons. They also consider conditions like temperature, depth and light. Finally, scientists determine the biotic (living) components of an area. They research which species have all or parts of their life history stages in that area. Areas that contain similar non-living and living components are considered an ecosystem type.

Using underwater imagery, grab samples and other scientific means, South African marine scientists have been able to distinguish over 15o specific marine ecosystem types in South Africa. The MzanSea project shares these broadly.

The ocean is three-dimensional

The ocean is three-dimensional. This means that unlike on land – where we generally move on the surface of the earth – in the water we can move up and down in the water column too. The African continent does not end at the coast but extends for kilometres out to sea under the water surface. The continental shelf gradually becomes deeper, until the slope where a drastic drop in depth at the shelf edge marks the transition from the shelf to the deep sea. South Africa’s continental shelf is variable and ranges from a very narrow shelf and shallow shelf break on the east coast to a wide shelf with one of the world’s deepest shelf edges off our West Coast. Across ocean ecosystems, the seafloor varies. The ‘substrate’ or the type of seafloor an ecosystem has, defines the type of seafloor community able to live there. Plants and animals are better able to attach to hard seabed, like rocky and gravel sea floors. On soft or unconsolidated seabed, like sandy and muddy ecosystem types, animals struggle to attach, and many bury themselves within the sand, mud or gravel instead.

This diagram details the three-dimensional nature of ocean ecosystems.

South Africa’s unique ocean environment

South Africa has a unique ocean environment.Two oceans meet at the southern tip of South Africa and the cold Atlantic Ocean on the West Coast converges with the Indian Ocean to the East. 

The West Coast of South Africa is influenced by the cold Benguela Current, travelling northwards past Namibia and Angola. While the Agulhas Current influences the East Coast, carrying warm tropical water southwards. South Africa also has an overseas territory in the sub-Antarctic region of the Southern Ocean called the Prince Edward Islands. The Islands are directly in the path of the longest and strongest ocean current in the world, the Antarctic Circumpolar Current. The Antarctic Circumpolar current connects three oceans (Indian, Pacific and Atlantic Oceans) and carries nutrients in a continuous loop around the earth. 

Because of these distinctive ocean conditions, South Africa is a special place for ocean exploration and new discoveries. 

Mzansea: revealing south Africa's marine ecosystems Logo

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