The Abyss


The Abyss, Die Afgrond, Enzonzobileni

Deepest, darkest plains where life is slow and there is still so much to discover

What is the Abyss?

The abyss is a distinct zone in the ocean, usually considered to start at a depth of between 3000m and 4000m and extending to 6000m. (Just think – that is 6km under the ocean surface!). Below this is the trench zone which is the deepest ocean zone extending to 11000m in the Mariana trench – the deepest part of the ocean. The abyssal plain is the flat, featureless area between the continental slopes and mid ocean ridges with chains of underwater mountains or seamounts making up distinct ecosystems within the abyss or slope. Abyssal plains form the deepest, darkest and coldest part of the ocean around South Africa although trenches in our sub-Antarctic territory in the Southern Ocean extend deeper into what is known as the hadal zone.

Deep ecosystems like the abyss have long been places of myth and legend. Recent scientific explorations into the depths of these ecosystems have found amazing creatures able to live in one of the harshest environments on earth. The South African geologist, Professor John Rogers, was the first to glimpse the South African abyssal plain when he took the first photographs of abyssal ecosystems using a camera in a specialised housing in 1988! 

Most of the abyss is made up of soft and fine sandy or muddy seabed, with scattered rocky areas providing essential habitats for creatures to attach. Similar to an oasis in a desert, boulders, cobbles, fossilised whalebones and small rocks are areas where a greater number of animals can live. These small rocks contain metal and are known as polymetallic nodules. They grow over millions of years as layers of the minerals – manganese and iron – are deposited around a core. These small metal nodules are of commercial mining interest because of the metals they contain.

Who lives in the Abyss?

Scientists are still learning about the creatures that live in the abyss with increasing evidence that there is actually high diversity especially in terms of bacteria, microbes and animals living in abyssal sediments. Scientists who sample the abyss report that it is typical to find more than 100 species in just 1m2 of seafloor sediment! Animals that live in the abyss are adapted to the harsh environment with very cold water (usually 1-3°C),  extreme water pressure, limited food and oxygen and absolutely no light. Water pressure increases at greater depths and animals must be able to withstand pressures as much as 600 times the water pressure experienced at the surface. Because there is no light, animals rely on food particles like those from decaying wood, dead animals and other organic matter falling from the upper ocean. Food also flows from shelf ecosystems. Just think, when a whale dies its body falls to the ocean floor where it becomes food for many animals. 

We do not know much about who lives on the abyss in South Africa. Elsewhere, camera and submarine systems have only explored a small portion of abyssal ecosystems. South African scientists are very excited to discover more about our deep-sea ecosystems. Most animals that live in the abyss are long-lived and slow growing. Life in the abyss is slow as this is an environment with little natural disturbance. Animals that live in the abyss are adapted to the darkness, pressure and limited oxygen and food. Scientists have discovered new species of sea cucumbers and worms at abyssal depths. Some of the most charismatic fauna include the seapig – a pink sea cucumber and giant isopods – large crustaceans that grow to be more than 15cm. Animals like brittle stars, starfish and sea urchins (all spiny-skinned echinoderms) feed on food particles that fall from shallower waters. Scavengers like crabs and shrimps feed on whatever organic matter they can find. Rattails are a common group of fish found in the abyss with snail fishes, tripodfish and greeneyes also occurring in the abyss. Some species of sharks, rays and chimaeras new to science, like the frilled shark, have recently been discovered in abyssal ecosystems. As there is no light in the abyss, many animals make their own light through special cells in their body. This is called Bioluminescence – animals that glow in the dark.

Why is the Abyss important?

Abyssal ecosystems are places  of deep mystery. Scientists think that tiny abyssal creatures (such as microbes) may play the most important role in  regulating the chemistry and climate cycles that allow life on our planet. There is great potential for new scientific exploration on abyssal plains with the chance of finding new species  previously unknown to science, new records (species known from elsewhere but discovered in South African territory for the first time) and creatures that may have applications in medicines or new technology. In Zulu and Xhosa culture, the deep sea is considered a sacred place where ancestors live

How do we care for the Abyss?

To care for these extremely deep ecosystems, we need to:

Build understanding and knowledge about the abyss: To care for the abyss we need to understand the system. Scientists are working to record which animals live in the abyss, better understand how the ecosystem functions and to identify research priorities. This will guide how we use the abyss and which areas in the abyss we should prioritise for protection. Support research to study abyssal plains and follow international research to learn more.

Protect portions of abyssal ecosystem types in Marine Protected Areas (MPAs): Protection of each abyssal ecosystem type in the Atlantic, Indian and Southern Ocean is important to provide reference areas to understand abyssal ecosystems. The Southeast Atlantic Seamounts,  Agulhas Front and Southwest Indian Seamount MPAs help protect parts of the Atlantic and Indian Ocean abyss in the Cape Basin and Agulhas Ocean Basin. Abyssal ecosystems in the Natal Valley and rocky parts of the Agulhas Basin currently have no protection in South Africa. New efforts are needed to protect unprotected abyssal ecosystem types.

Manage with precaution –  Abyssal ecosystems, because they are unexplored; require careful management that takes the limited knowledge and high uncertainty into account. A precautionary approach should be used. Life in the abyss changes slowly and if we impact these ecosystems through for example nodule mining we may destroy habitats for the unique animals that live on these nodules. As polymetallic nodules take millions of years to form, removing nodules may permanently remove habitats, meaning that these animals will probably never recover. New medicines have been found in newly identified marine species, we should preserve parts of the deep seabed to avoid losing  potentially important species. Seabed mining for polymetallic nodules is a growing concern as it may remove undescribed species. More research is needed on the abyss. Governments need to carefully consider the granting of approvals for seabed mining in the abyss, apply scientific research to guide decision making and make sure to establish and maintain protected areas for reference.

How do we learn more about the Abyss?

Studying the abyss is a relatively new science. Researchers are still making new discoveries and identifying all the many creatures that live in the abyss. Oceanographers, geologists, chemists and biologists are all hoping to understand and share more about this rarely studied ecosystem.

Dr Kirsty McQuaid

Abyssal scientist focused on impacts of deep-sea mining

Studied: Bachelor of Science (Rhodes University), Bachelor of Science, Honours (Rhodes University), Doctorate of Philosophy (University of Plymouth)

What is interesting about the ecosystem you are working in?

What is interesting to me about doing research in the abyss is that we are exploring unknown and mysterious places. We are seeing places that nobody has ever seen before. We do not know what many of the animals are, how they function or what services they provide.

What are the challenges with working in your ecosystem?

For my doctoral degree, I researched the impacts of mining in the deep sea, which is an emerging concern worldwide. Working on the issue of deep-sea mining is a unique opportunity to support environmental management of a new activity before it starts on a commercial scale. Now I am helping to classify and sample abyssal and other deep sea ecosystems by working with researchers across the South Atlantic.

What are you working on and why is it important?

Sampling the abyss is technically very challenging and very expensive. You might be surprised at the time involved in sampling these systems- it takes 5 hours just for the sampling gear to reach the seafloor. Abyssal scientists spend weeks away at sea apart from their families, to build the knowledge base for good decision making in the deep ocean.

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