Throughout human existence we have relied on the oceans for food, as a waste dump, for recreation, for economic opportunities and so on. However, its not only our activities in the marine environment that affect life in the sea its also the things we do on land.
Commercial fishing boat
Fishing was probably the first use of the oceans by humans. In the last century, significant increases in commercial fishing have resulted in the over-exploitation of many fish stocks. Some are feared to be extinct.
The international Maritime Organization estimates that more than half the worlds population now live within 100 kilometers of the coast, its not surprising that the activities of humans have taken their toll on the fish population. Human impacts have increased along with our rapid population growth, substantial developments in technology and significant changes in land use. Over-fishing, pollution and introduced species are affecting life in the sea and Nigeria is no exception!
Fisheries
Humans living near the coast have probably always used the ocean as a source of food. However, with advances in fishing equipment, larger ships and new tracking technologies, many fish stocks around the world have reduced significantly. Fish stocks on continental shelf areas are now widely considered to be fully or over exploited. Aside from reducing fish stocks, unsustainable fishing practices can have other negative impacts on the marine environment. For example, some fishing techniques such as dredging and trawling can cause widespread damage to marine habitats and organisms living on the sea floor. These techniques also often capture non-target species (known as by-catch) that are then discarded.
Unlike many other countries where fisheries are managed by quota system placing limits on certain kinds of endangered species, In Nigeria, the story is different where such limits does not exist.
Pollution
Our oceans have long been used as an intentional dumping ground for all sorts of waste including sewage, industrial run-off and chemicals. In more recent times, policy changes in many countries have reflected the view that the ocean does not have an infinite capacity to absorb our waste. However, marine pollution remains a major problem and threatens life in the sea at all levels.
Some marine pollution may be accidental, for example, oil spills caused by tanker accidents. Some may be indirect, when pollutants from our communities flow out to sea via stormwater drains and rivers. Some effects may not be immediately obvious, for example, bioaccumulation the process where levels of toxic chemicals in organisms increase as they eat each other at each successive trophic level in the food web.
All marine pollution has the potential to seriously damage marine habitats and life in the sea. Scientists are concerned that marine pollution places extra stress on organisms that are already threatened or endangered.
In Nigeria, sea pollution is a major threat to organisms living in the sea. Poor environmental systems affect the way waste is managed, especially residents who live in the south of the country who tend to dump refuse at waterways when rain falls and expect the rain to move the waste to the sea. This explains the large number of plastic debris that abound our seashore.
Eutrophication
According to the scientists at the international institute of maritime, Sweden, Eutrophication is the result of a particular type of marine pollution. It is caused by the release of excess nutrients into coastal areas via streams and rivers. These nutrients come from fertilisers used in intensive farming practices on land. Additional nutrients in the sea can lead to excessive phytoplankton growth that results in blooms. When these large numbers of organisms die, the sharp increase in decomposition of the dead organisms by oxygen-using bacteria depletes oxygen levels. In some cases, this can result in the death by oxygen starvation of large numbers of other organisms such as fish. Oxygen is essential even in the sea and laws has to be in place to curb such activities that stifle maritime organism.
Introduced species
Introduced species are unwanted marine Organisms. In Nigeria, introduced species in our terrestrial ecosystems have contributed to a significant loss of biodiversity. Introduced species also present a threat to our marine environment. It is not always easy to monitor or prevent the introduction of unwanted marine organisms, and visiting ships may introduce them accidentally on their hulls, in ballast water or on equipment.
Not all introduced species will spread or even survive, but once established, they may be difficult or impossible to remove. For instance, the Japanese seaweed, wakame Undaria pinnatifida, which probably arrived in 1987, is now widespread. Scientists are still monitoring its impact on their native marine organisms.
Ocean acidification
There is evidence to suggest that human activities have caused the amount of carbon dioxide in our atmosphere to rise dramatically. This impacts on the marine environment as the worlds oceans currently absorb as much as a third of all Carbon dioxide emissions in our atmosphere. This absorption of Carbon dioxide causes the pH to decrease, resulting in the seawater becoming more acidic.
Our role in ocean acidification
Scientists have long understood that an increase in carbon dioxide in the atmosphere will result in higher levels of dissolved Carbondioxide in seawater. However, a relatively recent discovery is that even small changes in water pH can have big impacts on marine biology. Ocean acidification is a worldwide issue, but as Carbondioxide is more soluble in colder water, it is of particular concern in cold temperate oceans.
It is difficult to predict the overall impact on the marine ecosystem but many scientists fear that ocean acidification has the potential to decrease marine biodiversity on a very large scale.
RESOURCES
Visit the Department of Conservations website to find out more about marine reserves and other efforts being made to protect life in the sea.
Forest and Bird publish the Best Fish Guide to help New Zealanders make sustainable choices when buying seafood.
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