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This section touches on various environmental issues.


The last three decades has seen the world’s costal zone systems degrading due primarily from human activities. Human and our activities when result in changes to the marine environment which causes harm to living resources and human health, hindrance to marine activities, quality of seawater and diminished of its uses are defined as marine pollution by the international group of experts on the scientific aspects of Marine Environmental Protection [1] One of the marine pollution is Marine Eutrophication, defined by the World Wildlife Fund as “a set of symptoms occurring when excessive nutrients stimulate plan growth which results in adverse environmental changes [2].

The Swedish Environmental Protection Agency ranks the current marine threats according to the effects that they perceived most important to human. They are mainly: impacts on biodiversity, impacts on access to natural resources, impacts on recreational values in the coastal zone, health risk and recovery time. Eutrophication had been ranked to be the top most factors that contribute to marine pollution. It was noted by the agency that eutrophication results in large scale oxygen depletion which will result in sever damage due to its chain effect, the accompanied algae blooms, ‘green tides’ and ‘red tides’ will make the water undesirable for both recreational usage and usefulness. But the agency felt that the risk of toxins releases by the microorganisms though will affect a large area, will pose little harm to human health [3].

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Table 1 Overall appraisal of effects of different disturbances in Sweden’s coastal and marine environment (Swedish Environmental Protection Agency)

Marine Eutrophication is caused by human activities, the discharge of substance of high plant nutrients. These discharge origins can be traced to three main sources: run offs from fertilized agriculture areas, sewage from cities and industrial wastewater from factories [4]. According to the European Environmental Agency, run off from agriculture lands contributed the most nitrogen release into the marine environment while phosphorous comes mainly from households and industries discharging their waste water into the marine environment.

Eutrophication is a process with several stages as mentioned by the European Environmental Agency. In the initial stage, the release of nutrient rich substance into the marine will result in increase growth rate of phytoplankton, phytobenthos, microorganism and herbivores [5]. The consequence will be algae bloom which creates a ‘shadow’ on the surface. These algae grow very fast and accumulate into very dense and visible patches on the surface of water. When the algae are mainly phytoplankton species containing reddish pigments, it will make the water seems as if it is red, which is known as ‘red tide.’ Though usually such a condition is harmless to human, it will cause the marine environment especially the coastal areas unsuitable for recreational activities and very unpleasant.

The other consequence of an algae bloom is the prevention of sunlight from penetrating to the deeper water areas resulting in reduced photosynthesis. This reduces oxygen production in the deeper water areas. Plants in darkness, does not produce but consume oxygen. And oxygen is also consumed by animals, aerobic microorganisms and decomposing dead organisms. As the deeper areas become unsuitable to support life, many will die and decompose, consuming more oxygen and eventually used up all available oxygen. In a study on the Baltic Sea, it has been discovered that eutrophication affects fish, like cod, that reproduce at deeper areas, resulting in reduce cod population [6].

In addition, some specific bacteria will then extract oxygen from sulphate in the water and release sulphur. These sulphur will then react with remaining oxygen on the upper areas forming sulphates. This chain effect will eventually consume all oxygen and all life will cease. Such effects can be spread from the immediate location of nutrient discharge to other areas due to current. In a study of the North Sea by NSTF observed that large amount of nutrients released at the shallow waters of southern North Sea also affected the waters of Eastern Skagerrak and Kattegar. This was due to the Jutland current [7].

The excessive growth of algae which includes micro algae, phytoplankton and cyanobacteria due to the increase in nutrients, also bring about the problem of toxins. Some of these organisms release toxins or are toxins themselves thus making the environment unhealthy and directly harmful to humans when consumed in large amounts. For example, cyanobacteria is both an algae and bacteria. Till date, 50 species of cyanobacteria is known to produce toxins, also known as cyanotoxins, harmful to animals and humans. Cyanotoxins can be classified into 3 types: Hepatotoxins, neurotoxins and dermatotoxins. Hepatotoxins is the more commonly known cyanotoxins. It will caused liver damage or death due to liver haemorrhage and cardic failure when consume in great amounts. But studies are still going on for the effects on humans when exposed to low level of hepatotoxins over an extended period of time. Neurotoxins causes sudden death by attacking the human’s nervous system resulting in cardiac arrests. Dermatotoxins caused allergy when in contact. In addition, some types of bacteria, under normal conditions, will be killed by ultra violet rays from sunlight thus rendering harmless to human and fishes. But under algae blooms, sunlight is not able to penetrate into the deeper areas of water and the bacteria began to survive and thrive. One such harmful bacteria is Escherichia coli can affect human bathing contaminated waters.

The more important consequence resulting from the toxins will be the accumulation of these toxins by shellfish and other seafood to an extent harmful to human health. The most significant of health problems caused by harmful algae are: Diarrhetic Shellfish Poisoning (DSP), Amnesic Shellfish Poisoning (ASP), Neurotoxic Shellfish Poisoning (NSP), Paralytic Shellfish Poisoning (PSP) and Ciguatera Fish Poisoning (CFP). Human are infected when they consume seafood containing these toxins, usually filtering shellfish like oystersm clams and mussels. DSP, though no fatalilty cases had been observed, is known to cause gastrointestinal symptoms. ASP can be life threatening. In mild cases, it results in gastrointestinal symptoms but in sever cases it can caused neurological disorders resulting in deaths. NSP can lead to muscular paralysis, state of shock or sometimes death. It is also one of the causes for massive fish death and other aquatic life. PSP, like ASP, is life threatening but it effects are neurological disorders. CFP produces gastrointestinal, neurological, cardiovascular symptoms and sometimes can result in dead but rarely [8]. This problem can be intensified if we take in account marine life like fishes consuming the shellfish and the toxins are carried over. The table below shows the cases of intoxication due seafood consumption.

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Table 2: Case of intoxication due to seafood consumption (HAP Technical Report 1996)

In mid of all the bad consequences mentioned above, there has been some arguments as to whether eutrophication increases or reduces the fish population. Increase in nutrients will increase plant growth which will in turn become food for the fish. Therefore logically, the fish will be able to thrive due to the increase in food availability. But some researchers argued that most of the fish feed on zooplankton instead of plants. Therefore if zooplankton is able to benefit from the increase of phytoplankton from the increase in plant growth, the fish population will increase. But the current technology does not allow effective and reliable methods of measuring zooplankton production [9].

In conclusion, the adverse effects of marine eutrophication will become a global problem if not kept under close monitor and control. And the best possible solution is prevention. If we can remove or minimize the source especially those caused by human activities, we will be able to prevent marine eutrophication. The need to preserve and protect our marine environment should be a global effort as the marine pollution has no boundaries.

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[1] Intergovernmental Oceanographic Commission, Marine Environmental Protection, website
[2] World Wildlife Fund, Eutrophication and Europeans marines sites, Marine 50 Update, 2001
[3] Swedish Environmental Protection Agency, Threats to the coastal and marine environment, Change beneath the surface (Mointor 19), 2005
[4] World Health Organisation, Eutrophication and Health, an article from < >
Hans W. Paerl, Coastal eutrophication and harmful algae blooms: Importance of atmospheric deposition and groundwater as ‘new’ hydrogen and other nutrient sources, Limmol Oceanogr. 42(5. part2), 1997, pp. 1154-1165
[5] European Environmental Agency, Integration of information on Europe’s marine environment, Technical Report 17, 1999.
[6] Marine Research on Eutrophication, A scientific base for cost effective measures for the Baltic Sea, Annual report 2000
[7] North Sea Task Force (NSTF), North Sea Quality Status Report, OSPARCOM, London, Oslen and Oslen, Denmark, 132pp, 1993
[8] Woods Hole Oceanographic Institution, Harmful Algae Page, a website from
[9] Nancy Marcus, An overview of the impacts of eutrophication and chemical pollutants on Copepods of the coastal zone, Zoological studies 43(2): 211-217, 2004

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