Considering more than two-thirds of our planet is covered by oceans, and it is a constant supply of food, energy and other resources, it’s alarming to realise that this underwater world is in danger.

You might only think of the ocean as a place to sail, surf or enjoy watching the sunset after a long walk on the beach, but there is a whole world beneath the surface that needs our help immediately.

In support of World Oceans Day, we take a look at the five biggest man-made threats to these huge bodies of water – and most importantly, what we can do to stop them deteriorating any further.

Overfishing

Fish and seafood might be a healthy choice for many people around the world, but the amount of fish and other sea creatures caught by humans is currently too high to allow for natural reproduction or replenishment. According to the UN’s Food and Agriculture Organization (FAO), around 30 percent of global fish stocks are overexploited or have already collapsed, and 58 percent are at their limit.

Whilst conventional agriculture might appear to be a good solution, industrial mass fish farming actually uses up huge amounts of seafood as feeding materials and could therefore make matters worse. Aquaculture farms also pollute their surrounding areas with excrement and facilitate the spread of fish diseases.

The saying “every little helps” really does apply here, as limiting the amount of fish and seafood you eat and staying clear of endangered species could help replenish their levels. Additionally, more rigorous fishing quotas and better fishery management could make a positive impact on increasing fish stocks.

Ocean acidification

Since the beginning of industrialisation, carbon dioxide emissions have increased significantly. Whilst the CO2 levels in the atmosphere have risen by around 40 percent, this level is much lower than it should be because a lot of the CO2 ends up dissolving into the oceans. When CO2 dissolves in water it increases ocean acidity, leading to a drop in pH, which has caused a number of sea creatures to die out.

The average pH of seawater has dropped by 0.1, yet this seemingly small amount is an extreme change to a lot of sea life, that in turn stops reproducing and eventually dies out. In 2005 for example, oyster farms along the Californian coast were forced to close because seawater there had become too acidic for oyster larvae. They died – and with them a whole industry.

Unfortunately the only way to tackle ocean acidification is to reduce carbon dioxide emissions, which can be done by reducing your red meat intake, making your household more energy efficient, buying local produce and walking, cycling or taking public transport wherever possible.

Global warming

Not only do the oceans store CO2, but they also store heat too. In fact, they absorb more than 93 percent of the heat generated by man-made CO2 emissions, which is causing the ocean’s waters to warm up. On average, the seawater surface temperature rose by 0.62 degrees Celsius (1.12 degrees Fahrenheit) between 1900 and 2008 – and this figure rose further in the Western Pacific Ocean.

Warming waters is a huge issue for many underwater organisms, including corals in particular. Corals are creatures that form a hard exoskeleton out of calcium carbonate. They harbour colourful photosynthetic algae inside which, when the surrounding water gets too warm, expel the algae. This causes coral bleaching, which is when the coral finally starves to death.

One third of the Great Barrier Reef in Australia has already been affected by coral bleaching. That’s the size of Italy! Just because it’s out of sight under the water’s surface, doesn’t mean it isn’t happening. The best way to tackle the warming water is to reduce CO2 emissions and support researchers who are working hard to learn about their reproduction and breed corals that are more resilient to warmer temperatures.

Pollution

If we keep producing (and failing to properly dispose of) plastics at our current rates, the amount of plastic in the ocean will outweigh fish pound for pound by 2050, according to a nonprofit foundation. This sickening statistic proves that the 5.7 million square miles of trash vortexes that have formed in the world’s oceans are not working, and as much as 99 percent of plastic waste never even reaches these areas.

A lot of it ends up on shorelines, thus polluting coasts and putting seabirds, turtles and wildlife in danger. Yet most of it decomposes or is broken up into tiny pieces – also known as microplastics – that is then ingested by sea creatures. If these mircoplastics don’t kill the fish or sea creature itself, chances are anyone who eats it will ingest it too.

Industrial farms are also responsible for letting other pollutants into the oceans too, including nitrate and phosphate which enter the oceans via rivers. These substances cause algae to bloom, and when the algae eventually dies, they are decomposed by bacteria which reduces the water’s oxygen content, ultimately meaning nothing else can grow there.

Industrial wastewater and emissions also add dangerous metals and chemicals to the oceans, including lead, mercury and persistent organic pollutants. The latter accumulate in the fat of whales, sharks and other animals.

The best way to tackle this issue is to reduce your use of single-use plastic, recycle, help organisations get rid of ocean waste and ask for stricter rules concerning wastewater treatment around the world.

Buried treasure

It might seem like there isn’t much more we can do to destroy our oceans anymore, but buckle your seat belts because things are about to take a turn for the worst. There are a number of valuable natural resources deep in the oceans that countries are already fighting to uncover. Manganese nodules (used for industrial metals such as stainless steal), cobalt, nickel and thallium are just a few elements that are known to exist deep beneath sea level.

Many countries have already secured claims on areas of the seafloor where they plan to begin mining operations as soon as the process is allowed and becomes economically viable. Yet research shows that these spots are hot spots for biodiversity, and mining operation could dramatically affect these delicate ecosystems. Strict rules on deep sea mining need to put in place to prevent the worst.