Currently, the problem of pollution of water bodies (rivers, lakes, seas, ground waters, etc.) is the most relevant since everyone knows the phrase “water is life”. People cannot live more than three days without water, but they still continue to rigidly exploit water objects, irrevocably altering their natural mode with discharges and wastes, even understanding the importance of water to human life. The water cycle has become disrupted with the development of civilization. Evaporation from land has increased as a result of crop irrigation. Rivers of southern areas became shallow. Pollution of the oceans and appearance of an oil film on their surface reduced the amount of water evaporated from their surface. All of this degrades the water supply of the biosphere. Today, water suitable for drinking, irrigation and industrial production is lacking in many parts of the world. Therefore, the problem of marine environment pollution is of critical importance in the modern world.
Oil and petroleum products are the most common pollutants in the oceans. By the early 80s, the ocean had annually received about 16 million tons of oil, which was 0.23% of world production of oil. Most of the oil, polluting the seas and oceans, is not a result of accidents or natural disasters, but a result of ordinary operations. During1962-1979, marine environment received about 2 million tons of oil as a result of accidents. Since 1964, about 2,000 wells have been drilled in the oceans, 1,000 of which are in the North Sea only. About 0.1 million tons of oil is lost annually due to minor leaks. Large masses of oil enter seas through rivers with sewage and storm water. Amount of pollution from this source is 2.0 million tons per year. Industry annually dumps 0, 5 million tons of oil together with sewage. When it gets into the marine environment, oil is first spread out as a film, forming layers of various capacities. Mingling with water, the oil forms an emulsion of two types: direct “oil in water” and reverse “water in oil”. Direct emulsions, composed of oil droplets up to 0.5 µm in diameter, are less resistant to typical oil containing surfactants. When removing volatile fractions, oil forms viscous inverse emulsion that can be stored on the surface, go with the stream, be thrown on the shore and settle to the bottom (Espedal, 1998).
Birds are particularly affected at the time of oil spills because oil permeates feathers, depriving birds of water-repellent and heat-insulating properties. Birds are unable to neither swim nor maintain the desired temperature of the body. Estimates of the number of birds, dying in oil spills, are often small, simply because the birds that got into trouble do not come to the attention of observers. When birds are trying to get out of oil, it sticks all over them, making it impossible to see and poisoning the whole body. Oil also pollutes or destroys the natural food sources of birds (International Maritime Organization, 2011). Diving birds are particularly affected, as they have to repeatedly dive through a layer of oil on the surface in search of food. Oil affects the entire ecosystem apart from the impact on individual aquatic organisms. Changes in the composition of the species of the maritime community are becoming noticeable in the areas where oil often falls into the water. Both oil and petroleum resins (tar) contain some carcinogenic substances. The results of several studies conducted on mollusks in polluted waters, indicate an abnormally large number of neoplasms, similar to human cancers, found in these animals (Belkin & Colwell, 2006).
The remaining inhabitants of the sea are less affected. Numerous studies have shown that oil creates neither constant nor long-term risk to organisms living in water and does not accumulate harmful substances in them, so it is impossible for them to get into a food chain of humans. According to recent reports, significant damage of marine flora and fauna can be applied only in certain cases. For example, oil products - gasoline, diesel fuel, and so on - are much more dangerous than crude oil. Typically, oil quickly diverges on the water in case of tankers catastrophes. Then, it is diluted with water and the oil expansion begins. It is proved that petroleum hydrocarbons could pass through the digestive tract and even through the tissues of marine organisms without harm. Such experiments were carried out on crabs, bivalve mollusks, different types of small fish, and no harmful effects were found in them (Programme des Nations Unies pour l'environnement, 2006).
There also numerous pollutants of the marine environment, such as mercury, pesticides, liquid and solid waste and radioactive substances. About 5 thousand tons of mercury, which is used in agriculture and industry, enters the ocean every day. Wastes containing mercury, lead and copper, are localized in some areas off the coast, but some part is imposed far beyond territorial waters. Mercury contamination significantly reduces the primary productivity of marine waters. Decrease in the number of tiny green algae, which synthesize organic compounds and release oxygen, is observed in areas of the highest concentration of mercury. Heavy metals are absorbed by phytoplankton, and then passed through the food chain to highly organized organisms (International Maritime Organization, 2011).
As a result, fish, marine mammals, birds can accumulate heavy metals in dangerous concentrations. Thus, some species of fish in the Mediterranean Sea contain two to three times more mercury than is considered safe according to the standards adopted by the World Health Organization. Owners of a Japanese chemical plant, located on Kyushu Island, dumped waste waters, saturated with mercury, into the ocean. As a result, coastal waters and fish were poisoned. Consumption of poisoned fish led to death of dozens of local residents; hundreds of people suffered from heavy paralytic diseases. In July 1972, a special commission officially confirmed 231 cases of diseases, including 59 fatalities (Belkin & Colwell, 2006).
World production of pesticides (chemical products used to destroy vermin) reaches 200 thousand tons per year. Relative chemical stability of many of these compounds as well as the nature of the spread has contributed to their entry into the seas and oceans in large volumes. Steady accumulation of organochlorine compounds in water is a serious threat to human life (Programme des Nations Unies pour l'environnement, 2006).
It was found that there is a balance between the level of water contamination by organochlorine compounds and their concentrations in fatty tissues of fish and marine mammals. Pesticides were discovered in various areas of the Baltic Sea, North Sea, Irish Sea, the Bay of Biscay, Spain, Iceland, Portugal and the west coast of England. DDT and hexachloran were found in significant amounts in liver and fat of seals and chinstrap penguins, although DDT is not applied in Antarctica. Vapors of DDT and other organochlorine compounds may absorb to suspended colloidal particles of atmospheric air or connect with aerosol particles and be transported to long distances in this state. Another possible source of the appearance of these substances in Antarctica may be marine pollution due to an intensive use of them in the U.S. and Canada. Toxic chemicals may reach Antarctica together with ocean water (Belkin & Colwell, 2006).
Liquid and solid waste (feces, sludge, and rubbish) is dumped in the seas and oceans directly from land, ships and barges. Part of these contaminants is deposited in a coastal zone, and another part is dispersed in different directions due to ocean currents and wind. Recently, pathogenic bacteria, bacterial intestinal pathogens and other diseases began to increasingly appear near major cities. This is a consequence of release of domestic wastewater into the sea without pre-biological treatment. Household scums are dangerous not only because they are a factor in the transmission of certain human diseases, mainly enteric (typhoid, dysentery, cholera), but also because they contain a significant amount of oxygen absorbing substances. Oxygen supports marine life. It is a necessary element for the process of decomposition of organic substances released into the aquatic environment. A significant reduction of dissolved oxygen, which is necessary for marine life, may occur if utilities scum gets into water in very large quantities (Beckman, 2013).
In recent decades, plastic products (plastic films and containers, etc.) have become a special type of solid waste polluting the oceans. These materials, being lighter than water, are floating on the surface for a long time and contaminate seashores. Plastic waste is a serious danger to navigation. They entangle the screw propellers of ships, clog up pipelines of the cooling system of marine engines and are often the cause of shipwrecks. There are known deaths of large marine mammals caused by mechanical obstruction of lungs by small scraps of synthetic packaging (Prager, 2003).
The extensive damage to fish stocks of the Mediterranean Sea is caused as a result of the increasing pollution. According to scientists from France, Italy and Spain, the number of fish in the sea decreases rapidly. Shallow sea fish like anchovies virtually disappeared; sardines are rarely found also. Poisoning of coastal waters makes them unsuitable for spawning. Over the next twenty years, $ 5 billion will be required to clean the Mediterranean Sea and prevent further pollution of its waters (Beckman, 2013).
The situation with the marine environment is different considering the radioactive substances. Radioactive elements may be present in water in the form of radioactive salts (discharged by factories producing nuclear fuel), as well as mechanical (blotches of radionuclides in the mineral particles) and biological contaminants (crustaceans that live in radioactive sludge water bodies) (Belkin & Colwell, 2006). Typically, radionuclides that get into the aqueous environment are unevenly distributed over the volume of water and infect all water organisms, particularly fish. Fish pollution occurs through direct adsorption of radioactive substances by the body surface through food and as a result of other metabolic processes between organisms and the environment. Radioactive elements penetrate through skin, gills and mouth into internal organs of fish (Vernet, Demers & De Mora, 2005).
An important source of fish contamination is a transfer of radioactive substances through food chains. Most fry and many adult fish feed on plankton, which can accumulate radionuclides concentration of which are hundreds or thousands of times greater than in the surrounding water. Therefore, radioactive substances affect fish primarily through contaminated food. Fish are exposed to an external radiation when they are placed in water contaminated with radioactive substances. Activity, which is adsorbed on the surface of their body, creates body irradiation. In its turn, radioactive substances, accumulated in organs and tissues, create an internal source of radiation (Capone, Bronk, Mulholland & Carpenter, 2008).
Radionuclides, as well as all stable nuclides, enter the body of aquatic organisms through the digestive tract, gill apparatus and epithelial tissue. The intensity of uptake of radionuclides is largely determined by physical and chemical properties of their stable nuclides. The intensity of uptake of radionuclides is also determined by their concentration in water, functional state of organisms, and so on. Living organisms metabolize nuclides of single element almost equally, since they are identical in chemical properties. The intensity of a radionuclide depends largely on the way of its penetration. Radioactive substances contained in a particulate matter are virtually not digested by aquatic organisms. In contrast, the radionuclides, which are in an ionic state, are rapidly absorbed by aquatic organisms (Capone, Bronk, Mulholland & Carpenter, 2008).
Global warming is the process of a gradual increase in the average temperature of Earth’s atmosphere and its oceans. Ocean as a habitat of marine organisms varies under the influence of climatic factors which include global warming. The scientific community has expressed a concern about the changes occurring in the marine ecosystems. The greatest effect on the ecosystems may be presented by an example of the coastal waters of Alaska.
Reduction of sea ice means a reduction in habitats of unique animals living on the ice. Ice seals, ringed seal, spotted seal, lionfish and bearded seal use ice for rearing, feeding, molting and rest. All of these factors make seals particularly vulnerable to the lack of ice. Walruses need sufficiently thin ice so that it could be cracked from the bottom for breathing, but at the same time it should be thick enough to withstand their weight. Ice should be over a sufficiently small water body (or cavity), so that a walrus can dive to the bottom of the sea or this cavity for feeding. Bearded seals also feed on the benthic communities, diving from ice platforms, which are appearing after cracking sea ice. A reduction in the pack ice in deep waters has caused a great damage to the both types of sea animals (Hassan, 2005).
Ringed seal is the only type of seals that regularly uses fast ice. They differ from other ice seals since they dig burrows and tunnels in ice floes to rest and grow cubs. Cubs are born in these maternity cameras on fast and steady pack ice in late March and early April and remain there for several weeks, protected from the harsh Arctic weather. As a result of global warming rains start earlier or ice starts to melt earlier, and if it happens when cubs are still in burrows, it can cause damage to offspring or result in population decline. In such a case, the offspring of ringed seals becomes an easy prey for polar bears. Ringed seal and bearded seal are staple foods of polar bear, which also eats other marine mammals. Regardless of the type of food, polar bears need ice as a durable surface for hunting. In addition, polar bears need ice in order to reproduce and move (Vidas, 2000).
Many polar bear cubs are born in dens on land. In the North Sea, ice fall is far away from the shore. When the space between pack ice and the shore freezes, polar bears are moving to the mainland. If the establishment of the ice in the coastal zone occurs later, and pack ice is too far from the coast at the same time, the mainland dens may be beyond the bears’ reach. As a result of warmer winters there is an increased probability of collapse of maternity dens because of the warm weather or late winter rain. Such a collapse has once killed a bear and newly born cubs. Like many other arctic animals, polar bears live long and reach sexual maturity very late. Increase in infant mortality of adult females, who reached puberty, causes serious changes in the size and structure of populations (Vidas, 2000).
Marine mammals need a protection from the cold in order to survive in the harsh environment of the North Sea. Global warming may be a cause of heat stress for some animals, especially bowhead whales. Due to higher temperatures seals and walruses that rest on the shore may suffer from overheating. Global warming will also lead to a greater spread of diseases. High temperatures promote the growth and development of parasites in marine mammals (Vidas, 2000).
Marginal waters contain a lot of food. Moreover, multi-year ice supports more complex subglacial communities than seasonal ice. Crustaceans at the ice edge feed seabirds and fish, in particular arctic cod. The latter is a key link in the food chain in the North Sea, but its life cycle depends entirely on the ice. This cod is an important food of beluga whales, ringed seals and bearded seals, seabirds and other species (Filatov, 2005). Large groups of arctic cod gather at the ice edge, attracting beluga whales. A reduction in multiyear ice and the length of the ice edge may lead to a loss of feeding habitat. The high productivity of ice edge allows birds and sea animals get food at a crucial time. Reduction of ice borders may also affect migration routes, so it will simply mean that food is not available at the right time (Filatov, 2005).
In 1977, unusually warm water temperatures in the Bering Sea caused a strong stratification of waters along the coast. As a result, zooplankton, despite its high biomass, turned out to be inaccessible to animals. It has disappeared from the surface layers of the ocean, which caused a massive loss of short-tailed shearwaters, since their main food was zooplankton. Warmer water temperatures and longer growing season can lead to the fact that some species of phytoplankton will gain an advantage over others. Change in the structure of phytoplankton communities may cause changes in the entire ecosystem (Vidas, 2000).
Warmer ocean waters will favorably influence the growth of some species of fish that will cause corresponding changes in the populations of fish-eating animals. At the same time, accumulation of fish may move to the north or dive in search of colder water into the deeper layers of the ocean due to the warming. Until about 1976-1977 (before water temperatures shifted to a warmer trend) it was unusual to catch a salmon in Wainwright, but now it does not surprise anyone. In 1997, thousands of seabirds in Alaska died of starvation. This was probably due to the fact that unusually warm surface waters caused a move of main food objects of birds into deeper water, making these objects inaccessible (Dallmeyer, 2006).
Climate change may affect bird populations not only through changes in spring and summer productivity of communities and food availability, but also through a change in their wintering conditions. The point is that the pack ice provides a successful wintering to a large number of seabirds. This is achieved by the fact that multi-year ice has more highly developed subglacial communities. Open water and gaps provide access to food for these birds. The warming effect on the subglacial communities is not studied yet. Scientists are trying to get information about what is happening in winter with sea and water birds. Perhaps, winter storms and blizzards kill birds not only directly, but also reducing the access to food (Vidas, 2000).
Despite millions of years of evolution, today marine organisms should quickly adapt to new conditions of life. The habitat of marine organisms is exposed to changes in two main aspects - the changes in their natural habitat and prey base, and changes in a chemical compound of the ocean. Marine plants, mainly plankton, are primary producers that form the base of the food chain. It is expected that there will be a gradual decrease in the number of these plants in the warm waters, which, in fact, will reduce the amount of nutrients available to the organisms of the next link of the food chain. Furthermore, the temperature is an important trigger in the life cycles of many plants and marine organisms. Frequently, processes of feeding, growth, and reproduction are consistent through time. If the synchronism of processes is broken, there is a risk that organisms can enter the “stage of life” when their food sources are not existent (Sapp, 2003).
The expected increase in ocean temperatures will cause a migration of marine organisms, which depends on their temperature tolerance – heat tolerant species will expand their habitat area in a northerly direction, and less tolerant species will simply withdraw from the usual places. Such a change in ocean dynamics will have a devastating effect on those species that are not able to migrate, and can lead to their death. Acidification of ocean water, i.e. increasing levels of carbon dioxide by reducing the pH of seawater, not only reduces the abundance of phytoplankton, but also reduces the accumulation of calcium salts in some marine organisms such as corals and shellfish, which leads to increased fragility of skeleton and stunted growth (Alevizon, 2010).
Global warming may cause the disappearance of coral reefs. Corals consist of a plurality of polyps, which together form the layer of a living tissue covering the calcareous skeletons. They depend on single-celled algae – zooxanthellae, which live inside the polyp`s tissue. Coral and zooxanthellae are interconnected with each other in order to survive; they have a symbiotic relationship in which corals are a habitat for algae and supply nutrients for them. In turn, algae supply corals with some products of their photosynthesis, providing them with an important source of energy. High water temperatures can block photosynthetic reactions in the algal cells, causing the accumulation of toxic oxygen species that threaten corals and can lead to loss of zooxanthellae. Without algae, corals will become white, a condition which is often called “bleaching”. Bleaching often leads to coral mortality, and mass coral bleaching will destructively impact coral reef ecosystems (Dubinsky & Stambler, 2010).
The real problem lies in the fact that deviations, caused by climate change, are superimposed on the marine environment, which is already under pressure from direct or indirect anthropogenic stress factors associated with overfishing (excessive fishing catches) and illegal forms of fishing, coastal development, land-based sources of pollution and the internal marine pollution. Such cumulative effects of multiple stress factors create extremely unfavorable conditions for the world’s coral reefs. About one-third of the colonies of marine plants and organisms, which cause the formation of reefs, are endangered. Currently, there is a significant reduction in the number of coral reefs throughout the world (Alevizon, 2010).
In the 21st century, the world entered the stage of development where the problems of survival and self-preservation of both mankind and the environment took the first place, as well as the reasonable use of natural resources. This stage of formation of mankind has revealed tasks activated by multiplying population and unsustainable use of natural resources. Pollution and violations of environmental links in ecosystems have become a global problem. If humanity will continue its current path of development, its destruction is inevitable in two - three generations. Therefore the most important condition for the formation of humanity is care for nature.
The main task today is to take precautionary measures, to raise public awareness of the impending threat and involve communities that are in real danger. It is vital in order to achieve changes in relation to the marine environment and human behaviors. Scientific knowledge should be converted into practical solutions that have to be supported by society. On a larger scale, governments and affected communities should collaborate in order to develop and implement policies aimed at long-term sustainable development. Any solution to the problems associated with pollution and global warming is simultaneously a solution to the problem related to the marine environment.