OCEAN VALLEYS
Canyons, Imiwonyo, Imiwonyo, Imihhume, Canyons
Pathways connecting life between the shallow and deep seas
What are Canyons?
Submarine canyons are deep valleys under the sea that cut into the slope and edge or margin of the continental shelf. They are shaped over very long time periods (millennia) by changing sea levels and bottom currents eroding the seafloor. Imagine a massive canyon – like the Fish River Canyon or the Grand Canyon – but under water. Several of these steep sided canyons cut into the slope and in some cases the shelf edge of South Africa’s West, South and East Coasts, acting as a path for resources and nutrients between the continental shelf and the deeper ocean- making canyons one of the most productive transport routes of the ocean.
In the absence of light or in low light conditions, canyons rely on organic matter either falling from the surface layer or flowing through the canyon from the continental shelf. The edges and steep slopes of canyons interact with currents and can be very productive.
The different types of habitats and the highly productive environment of canyons result in high biodiversity with rich communities on the edge or margins of canyons, on their rocky or sandy slopes and in the usually muddy canyon floor. Canyons are important spawning and nursery grounds for some fish and these productive valleys support high numbers of crustaceans, fish and large marine mammals.
Who lives on Canyons?
Submarine canyons have distinct bands or zones of animals occurring at different depths. Lining the steep rocky walls and margins of canyons are usually filter-feeding sponges and deep-water corals and sea fans. These animals provide food, shelter and points of attachment for many smaller species and are an important nursery habitat for fish and crustaceans. Many canyons are terraced, gradually stepping down with some flatter sections and then drop-offs as the canyon descends into deeper water. The bottom of a canyon is known as a thalweg. This soft usually muddy canyon floor hosts tall feathery sea pens, sea cucumbers and burrowing animals.
The highly productive waters of canyons and the diverse seafloor communities support commercially important fish including hake on the West Coast and seabreams on the East Coast. Canyons are home to a high diversity of fishes with many charismatic species like pineapple fish, john dory, slopefish and deep-sea goldies. These fish attract sharks and predatory fish like yellowtail and tuna. The South Coast Rock Lobster and the Natal Deep Water Rock Lobster are found in submarine canyons in the Eastern Cape and Kwa-Zulu-Natal respectively. Albatross and petrels travel from their sub-Antarctic breeding grounds to feed in the sea above the canyon- especially off the productive West Coast. Whales and other deep-diving marine mammals have also been found to use canyon ecosystems although this has not been investigated in South Africa. Canyons off the coast of KwaZulu-Natal are home to ancient lobed finned fish known as coelacanths.
Why are Canyons important?
Canyons are one of the most productive places in the deep sea and provide an important link between the shelf and the slope. They are significant in the life history of many animals including threatened animals like seabirds, turtles, whales and coelacanths. The role of submarine canyons in the life history of hake needs to be examined and canyons may play a role in protecting other commercially important fish species from fishing. Protecting canyon ecosystems not only protects animals we love to see but may also help maintain the fish stocks for species we love to eat. South African scientists are only starting to explore our submarine canyons and have yet to discover many species. Some of these may be important for new medicines or be important in bio-discovery research.
SOUTH AFRICA’S FAMOUS CANYONS
Cape Canyon (Off Saldana Bay, Western Cape)
Cape Canyon in the cold Atlantic on the Western margin is the largest underwater canyon in South Africa. This canyon is the same size as the Grand Canyon in the United States of America and 100 times bigger than the small canyons in the iSimangaliso Marine Protected Area.
Gxulu Canyon (off East London, Eastern Cape)
In December 1938 Marjorie Courtenay-Latimer, the Curator of the East London Museum, was called to the docks. A local angler, Captain Hendrick Goosen, had caught a very strange fish while fishing off the Tyolomnqa river. The strange specimen was like nothing she had ever seen before and she eagerly brought it back to the museum for identification. After some help from Professor J.L.B Smith in Makhanda (formerly Grahamstown), they identified the fish as one who was thought to have gone extinct almost 65 million years ago.
The strange fish, was the first scientific specimen of the Coelacanth, a deep canyon dwelling lobe finned fish, thought to still occur in the Gxulu Canyon.
Jesser Canyon (Off Sodwana Bay, Northern KwaZulu Natal)
In what is now protected by the new iSimangaliso Marine Protected Area (recently expanding the former St Lucia and Maputaland MPAs), is one of the most accessible populations of Coelacanths in the world.
In 2000, Trimix divers, exploring the canyon ecosystem at just below 100 m below sea level, spotted something they never expected to see. Long thought to live in extremely deep waters, one of the divers spotted what he was sure was a coelacanth. Further dives corroborated this story and a new research initiative, the African Coelacanth Ecosystem Program (ACEP) was developed to learn more about these ancient creatures and the offshore ecosystems in South Africa.
Today, researchers know more than 30 coelacanth individuals in the iSimangaliso MPA, recognised by their unique spot patterns. In 2019 and 2021, coelacanths were found at the edge of uMzumbe canyon and a canyon in the Protea Banks MPA in southern KawaZulu-Natal.
How do we care for Canyons?
There are many pressures that affect submarine canyons including bottom fishing, mining and petroleum activities and laying of submarine cables. To care for canyons we should:
Build understanding and knowledge about canyons: The key to ensuring that canyons and the animals living in canyons are cared for is to understand these ecosystems. Further research is needed in South Africa to better understand which animals live there and to understand the flow of energy and nutrients, water masses and tidal influence in these productive habitats. Support research to study canyons and follow international research to learn more. No-one has seen the uThukela canyon – imagine what we might discover there!
Manage activities that damage the seabed: Canyons have complex seafloor topography that is often home to long-lived, slow-growing animals. Cold-water corals, sea fans and other soft corals and sponges take years to reach a large size and are sensitive to activities that can affect the seabed like bottom trawling, bottom set longlines or traps and mining. Such species may indicate the presence of Vulnerable Marine Ecosystems which should be identified, mapped and managed. In order to understand and manage canyons, reference areas of canyons in good condition should be maintained in Marine Protected Areas.
Protect portions of canyons in Marine Protected Areas (MPAs): Reference areas of canyon habitat in good condition should be maintained in Marine Protected Areas. Parts of South Africa’s canyons are protected in the Cape Canyon, Amathole offshore, Protea Banks and iSimangaliso MPA.
How do we learn more about Canyons?
Canyons hold enormous potential for scientific discovery. The first coelacanths in South Africa were discovered in canyon ecosystems and scientists are still uncovering new information about them. Canyon scientists study an important system for fisheries resources and continuously make new discoveries that could benefit people. Multi-disciplinary studies that undertake geological, oceanographic, biodiversity and ecological research are helping to build the knowledge base for submarine canyons.
Sinothando Shibe
MSc Student at UKZN focused on the mapping of Seapen habitats
Studied: Bachelor of Science (University of KwaZulu Natal), Bachelor of Science, Honours (University of KwaZulu Natal )
What is interesting about the ecosystem you are working in?
Submarine canyons are like rivers under the sea. They transport sediments from the shelf to the deep sea. Upwelling and downwelling occur in submarine canyons – cool, rich water moves up onto the shelf and water flows from the shelf into the deep. You might assume that the deeper you go the less life you might find but canyons are full of surprises. Deep down there are steep walls covered in life with remarkable corals, delicate branching and amazing volcano-shaped sponges and beautiful fishes. One of the most interesting animals associated with canyons are the seapens- soft corals adapted to living in the sand that can be abundant at the sandy edges of underwater canyons.
What are the challenges with working in your ecosystem?
Submarine canyons are difficult places to work as they are deep under the sea needing offshore boats and special equipment. There are often strong currents that can prevent our sampling gear from reaching the seabed. We often use Remotely Operated Vehicles and this is difficult in the constantly changing depths of submarine canyons needing skilled pilot and crew and it is best if canyons have been mapped before we put gear on the seabed. I must often rely on photographs and video to undertake research but many canyon animals are poorly known. However, when we do make it into the canyon it is always worthwhile and there is the chance to learn more about these amazing ecosystems, discover new species and observe new behaviour!
What are you working on and why is it important?
I am researching the animals that live on that seabed in sand, mud and gravel habitats around and away from canyons. My research will help us understand the role of canyons in shaping these amazing animal forests (dense communities formed by animals rather than trees). I have found many seapens on canyon margins in the Eastern Cape and KwaZulu-Natal with fewer and different species further away from canyons. Elsewhere, other scientists have shown that these fields of seapens provide homes for fish, especially baby fish and play a key role in connecting ecosystems and energy flow. As habitat-forming animals, it is important to manage dense seapen communities so that they can continue to provide homes and nutrients for young fish, adult fish and other animals. My work helps map these special habitats and to work out where protection and management are needed. Good management of Vulnerable Marine Ecosystems (like seapen and other animal forests) helps eco-certified fisheries achieve certification allowing for greater economic benefits and longer-term sustainability.
Acknowledgements
The ACEP Deep Forests (NRF Grant 110765) and ACEP Deep Connections (NRF Grant 129216) are acknowledged for helping build the knowledge base for better management of submarine canyons and for providing resources to share canyon research with the public.
MzanSea 