10 need-to-know facts about… Life Below Water

Our blue planet is defined by its oceans. Sadly, the saying ‘plenty more fish in the sea’ could soon become obsolete.

1. Let’s start with some statistics

  • Oceans cover 70% of the planet Earth
  • Over 3 billion people depend on marine ecosystems to make their livings 
  • Oceans contain nearly 200,000 species that we know of. There may actually be millions.


They absorb about 30% of the carbon dioxide that humans produce, helping to reduce the impact of climate change. Which is a blessing and a curse. Unfortunately, the increase in CO2 has caused ocean acidity to rise by about 26% since pre-industrial times. And this acidification is causing big problems for marine species like coral. In fact, about 20% of the world’s coral has already been destroyed – with no prospects for recovery.

3. The plastic problem

It’s hard to quantify precisely, but scientists estimate there are over 5 trillion pieces of plastic currently littering our oceans. Two decades ago, a vessel descended into the deepest part of the ocean, the Mariana Trench in the western Pacific. At a depth of 10,988m, it found a single plastic bag. According to scientists, the bag will take up to 1,000 years to break down.

4. The plastic solution?

It’s early days yet, but work is underway to clean up the five massive rubbish patches in our oceans. One pioneering venture in this field was founded in 2013 by an 18-year-old Dutch inventor called Boyan Slat. His company, the Ocean Cleanup, is creating floating cleanup platforms he believes are capable of cleaning up 50% of the Great Pacific Garbage Patch within five years.

5. Welcome to the dead zones

Agricultural runoff and sewage flowing into the ocean create areas of low oxygen, dubbed “dead zones”. In these areas, marine life is unable to survive, and ecosystems collapse. There are now close to 500 such zones worldwide, with a total surface area of over 245,000km². That’s about the same size as the United Kingdom. 


Sadly, according to the International Union for Conservation of Nature, less and less so. Roughly 1,414 species of fish, or 5% of known species, are endangered.


Also known as the slimehead, this fish is native to the coasts of New Zealand, Australia, Namibia and the northeast Atlantic. Left to itself, it can live to the grand old age of 149. It reaches sexual maturity at somewhere between 20 and 32 years, which is, unfortunately, bad news for slimeheads. When fishermen trawl at their breeding grounds, they can wipe out entire generations.


Beluga whales, weighing in at up to 1.5 tons each, are extremely sociable mammals. They do everything with their pods, which can range in size from just a few in number to several hundred. Their signature bulbous foreheads (called “melons”) are flexible, allowing beluga whales to pull faces. These talented creatures can also whistle and chirp, a fact that has earned them the nickname “canaries of the sea”. Unfortunately, shipping and other human marine activity cause underwater noise pollution that interferes with their communication, making it harder for them to find food, find mates, and look after their young.


In 2015, in the small Madagascar village of Andavadoaka, locals who rely on fishing for their livelihoods were asked to close some of their favourite fishing zones for two months, allowing time for the species to breed and for populations to grow again. After the hiatus, they returned to fishing, and were surprised to find their catches had doubled in size. More importantly, their earnings tripled. Twenty other villages have now followed their lead.

10. Space invaders

With ever-expanding global trade, protecting ecosystems from invasive species is harder than ever. Scientists estimate there are 5,000 to 10,000 species traveling in cargo ships at any given time, floating in the ballast water used to keep the ships stable at sea. When the water is released on arrival, so are those living creatures. Zebra mussels are said to have attached themselves to the sides of ships travelling from Central Asia, then set up home in the Great Lakes of North America. There, they now clog boat engines, damage water pipes – and, most significantly, threaten native species.