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How much of the deep sea can we discover?

Getting to the bottom of things
The deep sea is both the largest and least studied habitat on earth, limiting the conservation and management of its ecosystems.

Food is scarce, and there is no sign of light. The pressure is equivalent to having a couple of elephants stand on your big toe. The temperature reaches just around freezing point (0°C). Yet, certain organisms flourish in this ecosystem by utilising and recycling these resources.

As technology has evolved over the last century, so too has our knowledge and discovery of the deep sea. The bottom of the ocean gives life to extraordinary ecosystems: communities that thrive in hydrothermal vents, organisms with photophore organs and the ability to undergo chemosynthesis using the ocean’s heavy metals.

While much of the earth’s ecosystems have been well-studied, we lack the same understanding about those in the ocean. The ocean covers over 70% of the earth’s surface, and much remains to be learned from exploring the mysteries of the deep.

This is curious given that the deep sea forms the largest habitat on the planet, covering over 50% of the sea’s surface and reaching over 4000m2 in depth.

In the mid-19th century, Edward Forbes set out on an expedition to investigate the distribution of life in the deep sea. Along the Aegean Sea, he concluded a simple finding: the deeper you are from the surface of the water, the more impoverished the natural flora and fauna becomes.

This was the infamous azoic hypothesis’ which stimulated debate and investigation among scientists and naturalists. In the years that followed, evidence of life in deep-sea systems accumulated. This era of exploration culminated in the eventual discovery of abundant sea life at deep levels, and an erroneous theory that was necessary to advance science.

We now know that the sea floor is teeming with life. Down in the black abyss of the ocean lurks an elusive sea creature which was first brought to surface in 2006.

The giant squid (Architeuthis dux) has been documented by sailors throughout history and is the largest living invertebrate (known so far). It measures up to 15m long, weighs over half a tonne, dwells 2100m below the surface, and has the largest eyes ever studied in the animal kingdom (measuring roughly the size of a soccer ball!). This is no surprise; such large eyes help the giant squid to survive and thrive in the depths of the ocean.

Giant squid bones

Professors Erling Sivertsen and Svein Haftorn measure a giant squid found in Ranheim, Norway in 1954 (NTNU Museum of Natural History and Archeology, 1954) 

Many other deep sea creatures have been observed, which tend to follow two trends: gigantism, like the giant squid, or dwarfism. Each faunal group has their own unique characteristics and have adapted to conserve their energy under such depths, allowing them to survive with limited food availability.

Although the deep sea remains relatively inaccessible, the impact of human activities on its habitats and communities needs to be considered. Global climate change has already started to degrade seascapes and shift habitats.

Mineral industries have begun to explore and exploit resources at increasingly deep waters of the ocean. Deep sea fishing has led to an up to 99% decline in deep-sea fish species over the last 30 years.

Yet the management and conservation of deep sea ecosystems is under-developed bdue to our limited knowledge on faunal composition, biodiversity, biogeochemistry and habitat distribution.

We cannot determine how to help protect deep sea species that are vulnerable to potential effects without expanding observations into its depths. With the commencement of the Ocean Decade, we have built on international scientific cooperation in order to preserve ocean health and understand the wonders of the deep sea.

Giant squid

Image of a live giant squid attacking bait (Tsunemi Kubodera, 2006). Adapted from: https://www.businessinsider.com.au/giant-squid-discovery-photos-history-2019-10?r=US&IR=T

9 July 2021