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Ocean Acidification

Oceans of our planet act as a natural carbon sink. The carbon-dioxide present in the atmosphere dissolves in the waters of the oceans. Thus, the oceans help lower the atmospheric CO2 concentration which, in turn, reduces the effects of global warming on the planet. However, as the atmospheric concentration of the gas is increasing, the oceans are becoming more acidic. This change in the pH of the ocean water can have disastrous consequences on marine life. Structures made of calcium carbonate might become vulnerable to dissolution in the acidic environment. This issue will adversely impact the corals and shellfish living in the oceans.



When the concentration of chemical nutrients increases in a water body, the process is called eutrophication. The change can lead to an excessive growth of plants and their subsequent decay. The dissolved oxygen concentration in the water also decreases due to eutrophication which induces the death of marine fauna. When the highly polluted rivers drain into the ocean, it might result in the formation of dead zones where the water is highly depleted of oxygen.

Plastic Debris

In the past few decades, plastic is one of the most dangerous pollutants that has been rapidly accumulating in the oceans. It is estimated that the mass of plastic in the oceans could be as high as 100,000,000 tonnes. All this plastic comes from numerous sources like discarded plastic bags, plastic cutlery, straws, six-pack rings, and more. All this plastic waste can pose a serious threat to the survival of marine fauna who can die by ingestion, entanglement, and suffocation. Plastic fishing nets are known to kill thousands of dolphins, turtles, seabirds, sharks, etc., in the oceans every year. Ingestion of plastic waste leads to the slow and painful death of these animals. Other pollutants also collect on the surface of plastic debris and magnify there. When such debris enters the human body through the food chain, it can have disastrous effects on the health of people.


There are several other toxins called persistent toxins that do not readily disintegrate in the ocean waters. Examples of such toxins are pesticides, DDT, phenols, heavy metals, PCBs, etc. When such toxins enter the body of marine animals, they accumulate in their tissues by a process called bioaccumulation. The toxins pass from prey to predator through the food chain and start biomagnifying at each higher level in the food chain. Humans are often at the top of many marine food chains and thus are the receivers of large quantities of biomagnified toxins from seafood.


Many species in the marine world rely heavily on their sense of hearing. However, human activities often introduce unnecessary noise in the marine ecosystem which is detrimental to life in the area. Noise can be generated by passing ships, seismic surveys, sonar, oil exploration surveys, etc. Such noise creates confusion in the marine world by interfering with the acoustic information on which these species rely for their survival.

Ghost nets

A turtle trapped in a ghost net, an abandoned fishing net. Fishing nets left or lost in the ocean by fishermen – ghost nets – can entangle fish, dolphins, sea turtles, sharks, dugongs, crocodiles, seabirds, crabs, and other creatures. These nets restrict movement, causing starvation, laceration and infection, and, in animals that breathe air, suffocation.


8.8 million metric tons of plastic waste are dumped in the world's oceans each year. Asia was the leading source of mismanaged plastic waste, with China alone accounting for 2.4 million metric tons.


Plastic waste has reached all the world's oceans. This plastic pollution harms an estimated 100,000 sea turtles and marine mammals and 1,000,000 sea creatures each year. Larger plastics (called "macroplastics") such as plastic shopping bags can clog the digestive tracts of larger animals when consumed by them and can cause starvation through restricting the movement of food, or by filling the stomach and tricking the animal into thinking it is full. Microplastics on the other hand harm smaller marine life. For example, pelagic plastic pieces in the center of our ocean’s gyres outnumber live marine plankton, and are passed up the food chain to reach all marine life. A 1994 study of the seabed using trawl nets in the North-Western Mediterranean around the coasts of Spain, France, and Italy reported mean concentrations of debris of 1,935 items per square kilometre. Plastic debris accounted for 77%, of which 93% was plastic bags. Further studies are being made around the world.


Nurdles, also known as "mermaids' tears", are plastic pellets, typically under five millimetres in diameter, that are a major component of marine debris. They are a raw material in plastics manufacturing, and enter the natural environment when spilled. Weathering produces ever smaller pieces. Nurdles strongly resemble fish eggs.

Deep-sea debris

Litter, made from diverse materials that are denser than surface water (such as glasses, metals and some plastics), have been found to spread over the floor of seas and open oceans, where it can become entangled in corals and interfere with other sea-floor life, or even become buried under sediment, making clean-up extremely difficult, especially due to the wide area of its dispersal compared to shipwrecks. Research performed by MBARI found items including plastic bags below 2000 m depth off the west coast of North America and around Hawaii.

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