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Unlock This CourseHumans have been using the ocean for thousands of years, but our impact has grown dramatically in recent decades. With over 7.8 billion people on Earth, our activities now affect every part of the marine environment - from shallow coral reefs to the deepest ocean trenches. Understanding these impacts is crucial for protecting our oceans for future generations.
Key Definitions:
Oceans cover 71% of Earth's surface and produce over half the oxygen we breathe. They regulate climate, provide food for billions of people and support incredible biodiversity. When we damage marine environments, we're not just harming fish and coral - we're threatening our own survival.
Scientists group human impacts on marine environments into several main categories. Each category represents different ways our activities harm ocean ecosystems, though they often work together to create even bigger problems.
Marine pollution comes in many forms, from the plastic bottles we can see floating on the surface to invisible chemicals that poison marine life. It's one of the most widespread threats to ocean health.
Industrial chemicals, pesticides and oil spills poison marine life. Heavy metals like mercury build up in fish, making them dangerous to eat. Even tiny amounts can disrupt reproduction and growth in marine animals.
Over 8 million tonnes of plastic enter our oceans each year. Sea turtles mistake plastic bags for jellyfish, seabirds fill their stomachs with bottle caps and microplastics enter the food chain at every level.
Fertilisers from farms create algae blooms that use up oxygen, creating "dead zones" where nothing can survive. The Gulf of Mexico has a dead zone the size of Wales caused by nutrient runoff.
This floating mass of plastic debris is twice the size of Texas, located between Hawaii and California. It contains at least 80,000 tonnes of plastic, including fishing nets, bottles and microplastics. Marine animals become entangled in the debris or mistake it for food, leading to injury and death. The patch demonstrates how ocean currents can concentrate pollution from around the world into massive environmental disasters.
Humans now catch fish faster than they can reproduce. Modern fishing technology allows us to find and catch fish more efficiently than ever before, but this has led to the collapse of many fish populations worldwide.
Overfishing doesn't just affect the fish we catch. When we remove too many predators like sharks, their prey species can multiply rapidly and upset the entire ecosystem balance. This is called a trophic cascade.
Bottom trawling drags heavy nets across the seafloor, destroying coral reefs and seagrass beds. Blast fishing uses explosives to stun fish but kills everything in the area. These methods cause massive habitat damage beyond just overfishing.
As human populations grow, more people want to live near the coast. This development destroys critical marine habitats like mangroves, salt marshes and coral reefs that serve as nurseries for marine life.
Coastal development also increases pollution runoff, changes water flow patterns and introduces artificial lighting that confuses marine animals like sea turtles trying to find the ocean after hatching.
Over 35% of the world's mangrove forests have been destroyed, mainly for shrimp farming and coastal development. In Thailand, mangrove loss has reduced natural storm protection, making coastal communities more vulnerable to tsunamis and typhoons. The loss also eliminated nursery habitats for fish, reducing local fishing catches by up to 80% in some areas.
Climate change affects marine environments in multiple ways. As we burn fossil fuels, the ocean absorbs about 25% of the carbon dioxide we produce, making seawater more acidic. This ocean acidification makes it harder for shellfish, corals and other creatures to build their shells and skeletons.
Warmer water holds less oxygen and causes coral bleaching. Many fish species are moving towards the poles to find cooler water, disrupting fishing communities and food webs.
Melting ice caps and thermal expansion of seawater cause sea levels to rise, flooding coastal habitats and human communities. Low-lying islands may disappear completely.
Climate change increases the frequency and intensity of storms, which can destroy coral reefs and coastal habitats that take decades to recover.
Humans accidentally transport marine species around the world in ship ballast water or attached to ship hulls. These invasive species can outcompete native species and completely change marine ecosystems.
The zebra mussel, originally from Eastern Europe, has invaded waterways across North America, clogging water intake pipes and covering native shellfish. They filter so much water that they've changed entire lake ecosystems.
The ocean is getting noisier due to shipping, offshore construction and military sonar. This noise pollution interferes with marine animal communication, navigation and feeding. Whales and dolphins rely on sound to find food and mates, but ship noise can mask their calls over vast distances.
The Great Barrier Reef has experienced multiple mass bleaching events since 1998, with the most severe occurring in 2016 and 2017. Rising water temperatures stress corals, causing them to expel their colourful algae partners and turn white. Without these algae, corals starve and die. Combined with pollution, coastal development and crown-of-thorns starfish outbreaks, these impacts have damaged over half of the reef's coral cover.
These human impact categories don't work in isolation - they often combine to create even worse problems. For example, climate change makes corals more vulnerable to pollution, while overfishing removes herbivorous fish that would normally control algae growth on reefs.
Understanding these connections is crucial for marine conservation. Protecting marine environments requires addressing multiple threats simultaneously, not just focusing on one problem at a time.
Despite these challenges, there's hope. Marine protected areas, sustainable fishing practices, pollution reduction and climate action can help restore ocean health. Young people like you are leading the charge for ocean conservation through beach cleanups, sustainable choices and demanding action from governments and businesses.