Threats to our oceans

The world’s oceans are fascinating and beautiful environments. Potentially we have yet to discover up to two-thirds of the species that occur in the marine environment. On top of that global oceans are essential for our survival. Over  3 billion people rely on the marine environment for their livelihoods. The oceans also provide the largest source of protein in the world, with over 2.6 billion people relying on fish as their primary source. But these important ecosystems are increasingly threatened by destruction. Presently about 40% of the global oceans are heavily effected by human activities. Without huge change to protect and mange marine ecosystems in a sustainable manner for the future, the percentage of  damaged or destroyed marine ecosystems will increase rapidly.


76% of the world’s fisheries are either depleted or overexploited (which means very soon they will be depleted). If the global fishing industry continues as it is at present, all stocks of fish caught for food are predicted to collapse by 2048. Overfishing is one of the biggest threats to the stability of marine ecosystems. Our demand for fish is ever increasing whereas total landed catches from global fisheries have been declining year on year since 1996. This is because more species are overfished and more stocks go into decline every year. In the UK we have been struggling for years to repair the damage caused by the overfishing of our cod stocks and finally in the last year or two there has been some improvement, although most of the UK stocks of cod are still overfished and should be avoided (have a look at my previous article to see what fish could replace cod in your fish and chips!). However, we may not be so lucky again and many other marine ecosystems have suffered devastating effects of overfishing.



Sea Level  Rise

The sea has risen 10-20 cm in the past century. The speed of the rising water has roughly doubled in the last 80 years compared to the previous 80. The rise by the end of this century is predicted to be anywhere between 0.8 and 2 meters, depending on how we as a global society tackle climate change and reduce global warming. The effects of rising sea level are obvious, the sea will slowly engulf our land masses. Particularly islands, like the ones found in the Pacific Ocean that only sit 3m above current sea level, may be completely flooded and the local communities will have to be relocated. In the UK we will see the increasing occurrence of events like the storm surge that happened last winter. Parts of the UK that suffer from coastal erosion will continue to be hit with increasingly bad erosion and a slow retreat from these coastlines may have to occur.


Ocean Warming
The surface layer of global oceans has been slowly warming since the 1800’s and the beginning of the industrial revolution. In the past three decades the sea surface temperature has been warmer than at any other time since reliable data began being collected. The temperature rises exacerbates sea level rise by speeding up the melting of ice at the poles and thermal expansion of warmer water. The warming temperatures can have devastating effects on species and completely alter the marine ecosystems that exist currently. One of the most well known effects is coral bleaching which is damaging coral reefs around the globe. In the UK, the effects can already be seen in stocks of many common species of fish found in our waters, such as cod and lemon sole. These stocks are either moving north out of UK waters or living deeper, adding to the already negative effects of overfishing and marine pollution on the stocks.

Ocean Acidification
The ocean has acted as a buffer from global climate change, absorbing large quantities of the carbon dioxide we release into the atmosphere. However, global oceans are beginning to reach their capacity to absorb carbon dioxide. Through a series of chemical interactions, the absorbed carbon dioxide causes the oceans to become more acidic. Ocean pH has already decreased by about 30% and could reach 150% by 2100, a pH that has not been experienced for over 400,000 years. The effects are already being felt by marine species that use calcium carbonate to build shells or skeletons, such as corals.


Over 80% of marine pollution comes from land-based activities. Marine pollution includes plastics, oil, sewage, chemicals and industrial waste. In developed countries oil spills, sewage, chemical and industrial waste are now relative well-regulated but accidents such as the BP Deep Horizon oil spill are still a problem. Old or inadequate infrastructure can also cause influxes of these pollutants into the oceans at specific times. Heavy rain in the UK can cause an influx of raw sewage into our seas when the old sewage systems cannot cope. In fact, everyday up to 300 million gallons of sewage enters UK coastal waters, which has undergone various levels of treatment. These pollutants are even more of an issue in less developed countries, where the policies and infrastructure are not present to prevent the pollutants entering the ocean. Marine litter is an increasing issue for the whole world. Eight million items of litter are being dropped into our oceans every day, which adds up to 6.8 million tonnes a year! Marine litter can accumulate in massive dumps due to ocean currents, in the central Pacific you can find 3 kilograms of marine litter to every 1 kilogram of plankton.


As well as overfishing which has been covered above, resource exploitation includes mining for minerals, metals and aggregates. As technology improves new and currently non-exploited environments are becoming targets for exploitation. Deep-sea mining of hydrothermal vents is one of the potential new targets to extract high concentrations of economically important metals. The biggest issue with extracting resources from these new environments is the lack of scientific knowledge abut how well the ecosystem will cope with the disturbance and pollution caused by the extraction. Every single hydrothermal vent produces a different mix or concentration of fluids, which means that each vent is populated by different species. The question remains that if we destroy one hydrothermal vent, will the species living on that vent be able to relocate and if they can’t what does this mean for the deep-sea ecosystem.


FAO The State of the World Fisheries and Aquaculture 2014 (

National Geographic website

UK Ocean Acidification Programme website

United Nations Rio +20 Oceans website (

Wood Hole Oceanographic Institute website

WWF website


Fish: NOAA

Bleached coral:

Deep-sea mining:

Marine rubbish:

Melting SeaIce: nasa


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Hannah Lawson

Hannah Lawson

I'm a marine biologist working as an Environmental Scientist for a marine consultancy. I love nature and the marine environment. I try to spend as much of my spare time outside and getting involved with conservation and outdoor activities.
Hannah Lawson

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