Deep Sea

For centuries, the wondrous creatures of the deep sea have inspired myths and legends of sea monsters, kraken and serpents. Others have even been thought to have gone extinct millions of years ago, just to be rediscovered in the deep sea.

The giant oarfish (Regalecus glesne) is the longest known bony fish with a body length reaching 8 m. Its body is narrow and elongated, allowing it to move through the water like a snake.

Because these fish are very rarely seen, and since they had not been described before the 1700’s, it is likely that they inspired the myths of giant sea serpents, often depicted on historic maps.

The Comoros coelacanth (Latimeria chalumnae) is one of the two coelacanth species still living today. Thought to have been extinct since the Cretaceous, its discovery by fishermen in 1938 caused an international sensation.

In contrast to the ray-finned fishes, the anatomy of coelacanth fins is particularly unique because they feature bones and muscles.

Scientists had long assumed that Coelacids were extinguished along with the dinosaurs at the end of the Cretaceous 66 million years ago.

The misleading term “living fossil” is often used for the coelacanth. This term refers to an organism that has retained specific—and often “primitive”—physical characteristics over a long period of Earth`s evolutionary history.

The giant squid (Architeuthis dux) was long shrouded in myth and mystery. Reaching 13 m in length, it engages in epic deep-sea battles with its greatest enemy—the sperm whale.

Each tentacle is equipped with suction cups studded with ring-shaped teeth made of chitin that allow it to capture prey and defend against attack, particularly from its primary predator, the sperm whale.

Scars bearing the pattern of a squid's suction cups are commonly found etched on a sperm whale’s thick skin—a testament to the ferocity of unseen battles in the deep sea.

In the realm of absolute darkness, light is used in various ways by different organisms: Some attract their prey, others use it to chase away attackers.

The alarm jellyfish (Atolla wyvillei) uses bioluminescence specifically to deter predators. Despite its small 18 cm diameter, it can prove to be a dangerous quarry.

If attacked, it reacts with bright, pulsating flashes of light that flicker around its umbrella-shaped bell. This response is an attempt to attract even larger predators to frighten off its attacker.

The Fire Salp (Pyrosoma atlanticum) is actually more closely related to humans than to jellyfish.
A single pyrosome is just 5 mm in size, but thousands of individuals aggregate to form tube-shaped colonies.

Every member of the colony has a pair of luminescent organs where bacteria of the genus Photobacterium are housed. When stimulated, these organs emit a bright rhythmic blinking of blue-green light.

The pelican eel (Eurypharynx pelecanoides) resembles a pelican's beak with a long tail because of its huge throat pouch. Its jaws comprise one quarter of its body length and are studded with small teeth.

. At the end of its tail, this fish has a luminous organ that emits a reddish-orange light. The glow is generated by a chemical reaction—the oxidation of the luciferin molecule—which produces light instead of heat.

The pelican eel positions this light organ in front of its gaping mouth as a lure and patiently waits for prey.

The barreleye (Macropinna microstoma) has extremely light-sensitive eyes that allow it to hunt in darkness. For protection, the eyes are housed in a transparent, gel-like dome covering the head.

The eyes are not fixed, but can rotate, allowing the barreleye to focus on its prey while swimming forward to capture it or to identify and escape a predator.

In
contrast to coastal zones where plants photosynthesize and numerous animals live, the deep
sea is a nutrient-poor habitat. The only food source are parts of animals or plants that
descend from the upper water layers. Without sunlight, other sources of energy become important, like the gases emerging from hydrothermal vents.

Endless silent plains of layered silt shroud approximately 70% of the seafloor. Contrary to appearances, these underwater “deserts” provide food and shelter to countless creatures.

Fish species inhabiting the soft bottom include the knifenose chimaera (Rhinochimaera pacifica)...

.. and the strange tripod spiderfish (Bathypterois grallator).

Some deep-sea creatures, like herds of sea pigs—a type of sea cucumber—can be easily identified by the tracks they leave in the silt.

Hydrothermal vents form in volcanically active submarine regions,
especially at the mid-ocean ridges. There, ocean water circulates
through cracks where the Earth’s new crust is being formed.

The water is super-heated up to 400° C, dissolving minerals from the rock and emerging as a hydrothermal solution. As it mixes with 2°C seawater, the suspended minerals are precipitated and form chimney-like structures, the black smokers.

The primary “producers” in this environment are sulfur bacteria, which use hydrogen sulfide and other minerals as an energy source. They can be found as symbionts in the digestive tract of these giant tube worms (Riftia pachyptila).

For many inhabitants of the deep sea, the arrival of a whale carcass from above marks the beginning of an epic feast.

Over the next centuries, the whale’s body will be consumed, decomposed and colonized by a wide variety of organisms.

For up to two years after a dead whale has sunk to the seabed, scavengers such as sharks and hagfish feed on the soft tissue of the carcass.

In phase two, smaller fish, crabs, giant isopods, sea cucumbers and octopuses comb the skeleton and surrounding silt for any edible remains.

The third phase can last from a few years to several decades as sulfur-loving bacteria penetrate the whale’s bones and convert the energy-rich lipids contained within.

Finally, over the following centuries, a mineral crust forms around the whale bones. The skeleton is now a rare and valuable hard substrate for sedentary deep-sea dwellers such as corals, sponges and sea lilies.

The deep sea is home to strange and beautiful creatures - as well as promising energy sources, rare metal deposits and commercial fish stocks. Deep sea mining and fishing pose a serious threat to its ecosystems. Senckenberg is researching
how these habitats could be effectively restored and repopulated to mitigate
long-term damage.

Deepwater coral gardens grow in near darkness, providing a habitat for countless species of fish, molluscs, crabs, echinoderms and microorganisms.

Deepwater reefs are extremely vulnerable to damage from bottom-trawling commercial fishing operations. The weights of the net ravage the ocean floor and cause destruction to deepwater coral reefs.

Recovery of these ecosystems is a long process due to extremely slow growth rates in such cold, dark habitats. A trawled seafloor can remain barren for decades.

This sediment contains methane hydrate, that is methane "frozen" in ice-like compounds. In this form, it is 160 times more concentrated than in its gaseous state, making it a very compelling energy source for the future.

Methane hydrate can be found frozen in marine sediments on continental slopes, often holding them in place like a kind of cement. Further analysis must determine whether mining could destabilize continental slopes, causing massive underwater landslides and triggering tsunamis.

This is a sea butterfly (Limacina helicina), a tiny snail of 11 mm length. They play a major role in the Arctic Ocean marine ecosystem. When they die, they sink to the seafloor and serve as a food source and building material.

Due to climate change, oceanic CO2 levels are also rising, reducing the pH value of seawater. Fragile organisms like the sea butterfly are highly affected by acidification as their shells become thinner and may break.

The deep sea and its inhabitants are as strange as they are beautiful. Senckenberg is involved in many research projects, leading to a better understanding and ultimately protection of this fascinating environment.

We hope you enjoyed the dive! If you want to find out more, visit the new exhibition at the Senckenberg Nature Museum in Frankfurt once it is open to the public again.