#marine gerology

[oupacademic]

Episode Two of Blue Planet II takes us to the deepest, darkest depths of the ocean floor, where crushing pressure, brutal cold, and pitch-black darkness make this one of the most extreme environments on our planet. Leading up to the episode this week, we’ll discover alien worlds, volatile landscapes, and a host of bizarre creatures that call this almost-inhospitable environment their home:

The first systematic deep sea exploration took place between 1872 and 1876, and was conducted by the Challenger Expedition on board the ship H.M.S. Challenger, led by Charles Wyville Thomson. The expedition led to the discovery of two new forms of deep-sea Ascidians (sac-like marine invertebrate filter feeders).

Benthic deep-sea environments are the largest ecosystem on Earth, covering approximately 65% of the planet’s surface and account for <95% of the volume of the biosphere. Increasing evidence suggests that global climate changes affect even this most remote of ecosystems.

Deep-ocean animals have adapted to the lack of light and scarcity of food in a number of ways. These include: greatly overdeveloped eyes, huge mouths, and being often equipped with numerous long, sharp, inward-pointing teeth.

Day-to-day you may not notice our bioluminescent aquatic friends, but in reality glow-in-the-dark critters comprise 5–59% of the abundance and 10–15% of the biomass in the world's oceans.

In addition to being home to a vast number of deep-sea critters, the Mid Ocean Ridge is also rich in minerals such as copper, zinc, and gold due to high amounts of volcanic activity.

The nature of a deep sea vent is dependent on the nature of the rock beneath. Most vents are Basalt-hosted, rich in sulphides and silica. However, ‘Rainbow’ in the Mid Atlantic Ridge is one of only two hydrothermal vents situated on ultramafic rock, causing more acidic fluid, rich in metals such as iron and manganese, and high in methane. Yet one species of shrimp has managed to adapt to call this harsh environment home.

In 2015, two new species of deep-sea starfish (Forcipulatacea) were discovered, including the first known sea star from hydrothermal vent habitats. This led to a new family and genus of starfish within the class Asteroidea.

Rubyspira osteovora is an unusual deep-sea snail from California, and has only been found on decomposing whales, thought to use bone as a novel source of nutrition.

While they may be one of the ocean’s most voracious predators, even the Humboldt Squid is feeling the impact of climate change. Squid habitats are becoming displaced as they respond to varying levels of ocean warming, and are having to find even deeper water to call home to avoid hypoxic waters and thermal stress in shallower waters.

Squid are the favoured food of sperm whales, and titanic struggles have been witnessed between them and giant squid. The giant squid may also have given rise to the Norwegian myth of the sea-monster, the Kraken. The cock-eyed squid has one big eye and one small eye, and its underside if studded with light organs. Cranchid squid are jelly-like and concentrate ammonia in their blood. This makes them neutrally buoyant, so they do not have to swim constantly. 

There is so much of our ocean yet to explore. Scientists are still finding new species in the depths of the ocean – such as new crustacean genus’ and species in the Abyssal depths in the Japan trench.  While there is much we still don’t know about the deepest, darkest parts of our oceans, one thing we do know is that deep sea farming can be detrimental to those species of both flora and fauna that call those parts home.

Images: 1) Champagne vent white smokers by NOAA. Public domain via Wikimedia Commons. 2) Octopus by glucosala. Public domain via Pixabay. 3) Chauliodus sloani abissal fish arriving in surface waters in the Straits of Messina (permission of prof. Francesco Costa). CC BY-SA 3.0 via Wikimedia Commons. 4) ALVIN submersible by NOAA. Public domain via Wikimedia Commons.