10 Amazing Facts About the Deep Sea and Its Threats

Our Deep Sea – What's It All About?

The deep sea is the habitat in the ocean where no sunlight penetrates. Scientifically, you are in the deep sea from a depth of 200 meters - even though our oceans are on average 3,688 meters deep. In terms of volume, the majority of our oceans are deep sea. Despite the darkness, it offers a variety of life and is a spectacular ecosystem that is definitely worth a closer look: Here are ten amazing facts about the deep sea.

1. The largest habitat on our planet

The ocean is already the largest habitat on our planet in terms of area, covering 71% of the earth's surface. In contrast to rural habitats, we are in three-dimensional space in the water. This means that the depth dimension means there is much more space that animals can use. If you include the third dimension in the calculation, the ocean offers 99% of all possible habitats. Due to its enormous depth, 95% of the ocean is below 200 meters and therefore in the deep sea. This therefore contains by far the largest habitat on our planet.

2. Ghost nets in the deep sea

In the deep sea ghost nets pose a particular danger because they cannot be recovered and decompose even more slowly. These are abandoned, lost or discarded fishing nets that end up in the sea. Even without human use, these non-biodegradable nets become deadly traps for all kinds of marine life. The animals get caught and die without ever being used by humans. Depending on the study, the time varies from days to years. Many sink into the deep sea. Since biological degradation processes are slower there than in higher water layers, ghost nets exist for a particularly long time in the deep sea. The nets that end up on the bottom of the deep sea change the habitat in the long term. It becomes more difficult for many species to colonize the bottom and many animals die in the nets. Ghost nets are becoming more and more common in shallow waters. recovered , but this is not possible in the deep sea.

3. Deep Sea Mining – Threat to an Unknown Ecosystem

Deep sea mining is threatening the previously barely explored deep sea ecosystem. Our everyday lives and our economy need more and more resources. The deep sea has now become the focus of resource extraction. This is because there are countless so-called polymetallic nodules there. These are rich in manganese, iron, cobalt, nickel, copper and titanium, among other things. As these metals are becoming increasingly scarce on land, interest in the previously little-explored deposits in the deep sea is growing rapidly. But deep sea researchers are concerned. So far, too little is known about deep sea mining and its consequences for the biodiversity and functionality of the ecosystem. Such mining could degrade the ecosystem before humanity has even understood it. We take a closer look at the exact effects of deep-sea mining in our Ocean Crime Podcast.

4. The International Seabed Authority as a decision-maker for activities in the deep sea

The International Seabed Authority (ISA) is an intergovernmental organization that regulates all activities in the deep sea outside of national jurisdiction. As of May 2022, it has already issued 31 contracts to explore this ecosystem for deep-sea mining. There are no contracts for actual mining yet. But that could change in the next few years. The IUCN assumes that deep-sea mining could begin as early as 2026, although sustainable extraction of the metals is hardly conceivable at present.

5. Single-celled organisms as a food source in the deep sea

Photosynthesis, which is so important for life, is carried out on land by plants and trees. In the ocean, these primary producers are mainly single-celled algae, the phytoplankton. The majority are only 1-70 micrometers (one micrometer is equal to 0.001 millimeters) in size and cannot be seen with the naked eye. Since they need sunlight for photosynthesis, they only live in the upper 200 meters. When a single-celled organism dies, it begins to sink. Many appendages are attached to their bodies. As the single-celled organisms sink, these appendages hook onto other microscopic dead organisms. They combine to form larger particles that look like small snowflakes in the water and are therefore often referred to in science as “marine snow”. The sinking single-celled organisms make up the majority of organic material in the deep sea and form the basis of the food web. However, other sinking dead animals, such as whale carcasses, also attract a large number of animals and provide them with a source of food for a long period of time.

6. Pitch black and bitterly cold

The deep sea is an extreme habitat and therefore leads to strange but very clever adaptations of its inhabitants. With an average temperature of just 4°C, it is bitterly cold. There is no light. Due to the lack of photosynthesis, there is a lack of food. Due to these difficult living conditions, deep-sea organisms have become real survivors. They have adapted perfectly to this hostile ecosystem. Around three quarters of all deep-sea creatures are bioluminescent: they produce their own light through an enzymatic reaction. Others have huge mouths and teeth, which they use to eat much larger prey when food is scarce. Because it is so dark, many deep-sea organisms either have gigantic eyes - or none at all. The animals camouflage themselves in transparent or red colors. This is because red is the first color to be absorbed in the ocean. Therefore, red animals appear black at a certain depth and are perfectly camouflaged.

In the family of anglerfish, the red coloration and the abnormal size of the mouth relative to the body size are easily recognizable. © Masaki Miya et al. 2010

7th The deep sea as a source of nutrients

The deep sea is largely responsible for the productivity of surface waters - you can find out how here: The single-celled algae not only need sunlight to survive, but also nutrients. If there is a lot of sunlight available, the available nutrients determine the growth of these algae. This means that only as much photosynthesis can take place as the nutrients allow. When deep-sea organisms eat the sinking marine snow, the nutrients are returned to the water with their excretions. They are then available again for photosynthesis. At least in theory, because the lack of sunlight in the deep sea means that no photosynthesis takes place there.
However, there is a solution: For example, at underwater mountains that rise from the deep sea towards the water surface, nutrient-rich water from the deep sea returns to the surface. These so-called upwellings promote primary production enormously and support a huge diversity of species. These biodiversity hotspots are now fishing or tourism strongholds. But an underwater mountain is not always necessary. They can also be created by other oceanographic conditions.

8th Predators – the link to the deep sea

Many marine predators that were previously thought to be found on the surface of the sea regularly dive into the deep sea: whales, dolphins, penguins, elephant seals and sea turtles. But also sharks, swordfish and tuna. The rare beaked whales even dive to depths of almost 3,000 meters. Due to the extreme conditions (pressure, temperature, reduced oxygen levels, lack of light), the dives are physiologically extremely challenging. So why do all these animals still go on these daily excursions into the deep sea? Most scientists assume one main reason: hunting. Swordfish hunt deep-sea fish, sperm whales eat giant squid and blue sharks hunt squid. On the one hand, the deep sea is therefore an important source of food for the predators. On the other hand, the dives enable nutrients to be exchanged between ecosystems.

9. The destructive power of deep-sea fishing

Just one fish and thousands of years of growth are destroyed. Deep-sea bottom trawling is a huge problem because it gradually kills all the animals that live on the seabed and destroys the habitat there in the long term. The target is usually medium-sized deep-sea fish that live on deep underwater mountains close to the bottom. A bottom trawl can weigh up to four tons and ensures that the seabed is level with the ground. Corals, sponges and other seabed dwellers can hardly recover from this stress. Some of the organisms live up to thousands of years and grow very slowly. Just a few uses of these nets destroy an ecosystem that will need thousands of years to fully recover.

10. The threat of climate change

Climate change is also making itself felt in the deep sea. The deep sea is getting warmer, it soured and has less oxygen available. Due to the complex oceanographic conditions and nutrient flows, the consequences are difficult to predict in detail. Researchers expect the loss of habitats, poorer food supplies, a reduction in growth and reproduction of various species and ultimately a decline in biodiversity. In addition, Ocean acidification . Due to the changed chemical environment, many calcifying deep-sea organisms, such as crustaceans, can hardly form their calcareous skeletons. Despite the apparent distance from anthropogenic CO2 emissions, the consequences of climate change are already clearly noticeable in the deep sea.

The deep sea is a gigantic, fascinating place with a biodiversity that we have barely gotten to know, let alone been able to decipher in its complexity. But if we want to use and protect this habitat sustainably, we must understand it as well as possible. Otherwise, we risk unsustainable resource extraction, which has already caused mass species extinction in other ecosystems.

CONTRIBUTION BY LENNART VOSSGÄTTER

Lennart is a master's student in marine biology at the University of Bremen and is researching the population ecology of tiger sharks. He has a passion for diving with sharks and spent five weeks on the Azores, a volcanic island group in the middle of the Atlantic, as part of a scholarship from Bracenet. There he studied and photographed the marine megafauna.

SOURCES:

Angiolillo, M. (2019). Debris in deep water. In World Seas: an Environmental Evaluation (pp. 251-268). Academic Press.

Braun, CD, Arostegui, MC, Thorrold, SR, Papastamatiou, YP, Gaube, P., Fontes, J., & Afonso, P. (2022). The functional and ecological significance of deep diving by large marine predators. Annual Review of Marine Science , 14 , 129-159.

Clark, M. (2017). Deep-sea seamount fisheries: a review of global status and future prospects. Latin American Journal of Aquatic Research, 37 (3), 501-512.

IUCN (2022) Deep sea mining. International Union of the Conservation of Nature , https://www.iucn.org/resources/issues-brief/deep-sea-mining.

Levin, LA, Wei, CL, Dunn, DC, Amon, DJ, Ashford, OS, Cheung, WW, ... & Yasuhara, M. (2020). Climate change considerations are fundamental to management of deep‐sea resource extraction. Global change biology , 26 (9), 4664-4678.

Miya, M., Pietsch, TW, Orr, JW, Arnold, RJ, Satoh, TP, Shedlock, AM, ... & Nishida, M. (2010). Evolutionary history of anglerfishes (Teleostei: Lophiiformes): a mitogenomic perspective. BMC Evolutionary Biology , 10 (1), 1-27.