The coronavirus pandemic has been dominating headlines recently, but it's not the only pressing problem that affects the whole planet. The damage we are doing to our oceans also threatens our existence.
They help to provide the air we breathe, the food we eat and the fuel that powers our world. Life could not exist without them, but our oceans are under threat.
On World Oceans Day, we celebrate our seas and look at why we need to protect them, now more than ever.
Rainforests are often referred to as the lungs of the Earth, but tiny organisms in our oceans produce more than half of the world's oxygen.
The oceans and the life within them also absorb about a quarter of the carbon dioxide we release into the atmosphere.
That helps to reduce the amount of CO2 in the Earth's atmosphere, protecting us from global warming. But it comes at a cost.
When oceans absorb CO2, they become more acidic. Today, oceans are more acidic than they have been in at least 800,000 years. This acidity affects marine species -- including plankton, shellfish and corals -- that build their shells and skeletons from calcium carbonate.
It's essential that we reduce CO2 emissions, and we can all take concrete actions to make a difference.
Fueling our world
Offshore wind farms, and wave and tidal power have huge potential to provide renewable energy for a world that needs to cut down on fossil fuels.
The oceans are a significant source of those fossil fuels, with more than a quarter of all our oil and gas coming from offshore sources.
But millions of gallons of oil are released into the oceans each year. This comes from a number of sources, including natural seeps, drilling, and spills from ships and pipelines. Oil from roads and storm drains also flows into the sea.
Oil spills can be deadly for sea life. Dolphins can inhale oil, damaging their lungs. Oil harms fish, traps turtles and can make birds' feathers unable to repel water, causing them to die from hypothermia. After a spill, it can take decades for an ecosystem to recover.
Making the weather
Covering around 70% of the Earth's surface, the oceans play a vital part in regulating our climate. They keep temperatures from getting too hot or cold and their water evaporates to form vapor that can travel vast distances before falling as rain.
By absorbing heat the oceans are also a buffer against global warming. More than 90% of the warming that has happened on Earth over the past 50 years has occurred in the ocean. But the extra heat is making ocean water expand, causing sea levels to rise and threatening coastal communities around the world.
And when seas get too hot, marine life suffers. Corals can starve and turn deathly white. In recent years, reefs around the world — including half the corals on the Great Barrier Reef — have experienced mass bleaching events.
So far, scientists have identified around 250,000 marine species, but more than 80% of the ocean is still unexplored and researchers estimate that nine in 10 ocean species have yet to be classified.
However, pollution is damaging ecosystems and harming wildlife.
Millions of tons of plastic end up in the oceans every year, killing and injuring sea creatures. Tiny pieces of plastic can be ingested by marine life, with potentially harmful effects.
Fertilizers wash from farmland into the sea, where they can feed vast blooms of algae. By using up the oxygen in the water, blooms like these have created more than 400 ocean "dead zones," together making up an area bigger than the United Kingdom. These areas are so starved of oxygen they can barely support marine life.
Feeding the planet
Globally, around 15% of the protein we eat comes from seafood. With a growing human population and the development of industrial-scale fishing technologies, twice as much seafood is eaten now than in 1970.
Commercial fishing has led to more than 90% of marine fish stocks becoming fully fished or overfished.
Overfishing tends to kill off larger fish and reduce reproduction rates, further depleting fish stocks.
It also threatens the hundreds of millions of people who depend on fishing for their food and income.
It's not too late
The situation may look bleak, but it's not too late to make a difference.
In April, a team of scientists from around the world found that marine life could recover to healthy levels in the next 30 years if pressures on the world's oceans -- including climate change -- were addressed.
Researchers recently reported that many coral reefs can still be saved if marine protected areas are established and fishing is better regulated.
Technology has a role to play. Scientists in the United States have developed the "Oleo Sponge" -- a reusable device that could help to clean up spills. Last year, Ocean Voyages Institute used satellite and drone technology to remove more than 40 tons of plastic from the Pacific Ocean.
But we need each other, as much as we need technology, to clean up the mess we've made. Around the world, volunteers are giving up their time to remove plastic waste from beaches and rivers.
While there are countless threats to our seas, there are also many opportunities to find solutions. Our oceans give us life, but it's up to us to protect them.