Oceans cover about 70 per cent of the Earth's surface, accounting for most of the Earth's water and making up more than 97 per cent of the biosphere. The oceans nurture life and shape the planet's weather and climate. They create more than half of our oxygen and provide vital sources of protein, energy and minerals. As described by some, ‘Earth is a marine habitat’. The oceans provide food for a billion people, and are also a source of income and livelihood for millions. The FAO estimates that about 200 million people are employed in capture fisheries and aquaculture, and in related secondary activities.
But oceans are experiencing serious environmental challenges, many of which have unknown consequences. In 1990, a report by the Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) on the ‘State of the Marine Environment’ highlighted coastal pollution as the principal threat to the marine environment. In 2001, the same group of experts, while recognising that land-based activities continued to be the principal source of pollution, and anticipating the consequences of global warming, acknowledged that pollution is not the only, or even the most severe, threat to the oceans, and that direct physical damage to ecosystems and habitats and over-exploitation of the resources ‘have even greater worldwide effects’.
Current scientific literature acknowledges the existence of a more complex set of interactions between humans and the marine environment. The principal threats and stresses include: (1) overfishing; (2) habitat loss; (3) pollution (mainly coastal); (4) introduction of invasive species; and (5) climate change. The percentage of stocks fished at biologically unsustainable levels has increased continuously since the 1970s, with more than 30 per cent of stocks estimated as being overfished in 2013.
Habitat destruction results from direct removal of habitat, including from damaging fishing practices, such as bottom trawling, but also from the alteration of the environment through activities that change inputs into the oceans or interfere with their natural functioning, including pollution.9 The largest source of pollution comes from land-based activities. In coastal areas, the release of nutrients into the water, causing eutrophication, and increased microbial activity through the provision of organic matter are the source of severe problems.