The impacts of oil pollution on marine ecosystem can be categorized into long term and short term effects.
Environmental effects of oil spills on marine ecosystem
Suffocation cause by oil spills and oil poisoning are among the first group. Because oil floats on top of water, less light penetrates into the water, limiting the photosynthesis of marine plants and phytoplankton. Oil spills reduce oxygen absorption of the water, causing oxygen dissolution under oil spills to be even less than the deep sea levels.
The oil penetrates and opens up the structure of the plumage of birds, reducing its insulating ability, and so making the birds more vulnerable to temperature fluctuations and much less buoyant in the water.
It also impairs birds' flight abilities, making it difficult or impossible to forage and escape from predators.
Suspended oil can gain weight by bonding with minerals and settle on the sea floor and harm the ecosystem there. Also causes sediments adherence to the sea floor, destabilizing plants. Usually it has been observed that sediments begin to move after oil settles on the sea floor.
An oil effect on coastal vegetation is also important. Algae and other local plants have been reported to be eradicated.
Animals that come in touch with high concentrations of oil die of oil poisoning.
Worms, microorganisms and young sea creatures are more sensitive.
Humans and other animals living near the sea are also threatened.
Among these compounds, cyclic (aromatic) hydrocarbons that low boiling point are more dangerous, such as benzene, toluene and xylene.
Naphthalene and Phenanthrene are more poisonous for fishes than the mentioned compounds.
Aromatic compounds are more soluble in water than saturated hydrocarbons; therefore creatures may become poisoned without direct contact with the oil by the polluted water. Fortunately these compounds are volatile; their harmful effects will decrease with time.
On the whole, a large oil spill will poison and kill a great deal of sea creatures in a short duration (in several hours, even minutes).
Corpses of fishes and crabs are washed ashore.
Long term effects of low concentration pollutions will reveal themselves in a longer duration.
Thin oil sheens can dissolve fat soluble poisons such as pesticides and increase their concentration several times higher than usual and more than tolerable for most of the living creatures.
Studies investigating the organic components entering food chains shows that they persists in living creatures and can pass through several food chains without changing.
These compounds, such as pesticides and heavy metals can be accumulated and finally will transfer to creatures used as food by humans and thus they will be accumulated in the human body.
Effects of oil compounds on marine animals
It's been proven that oil compounds will harm marine organisms even in low concentrations.
Organisms accumulate oil compounds in their body through water, sediments and their food.
Some oil compounds are poisonous depending upon their type or whether they are refined or not, which will increase their toxicity compared to petroleum.
For example, there are evidence that oil materials affect reproduction, growth and behavioral characteristics of many animals, especially eggs, larvae and other intermediate growth stages.
Oil compounds increase disease sensitivity in fishes and prevent growth of the phytoplankton. Widespread oil spills can have a devastating effect on marine organisms, especially those in coastal regions.
Marin birds and mammals like seals are very sensitive, many of these animals will die if they furs or feathers are covered with oil, because they will loose their insulating ability.
Birds that depend upon flying for food will die of starvation. It's difficult to estimate the number of birds' casualties, because many drown in the sea before being washed ashore to be counted.
After an oil spill from AMOCO CADIZ oil tanker, about 3200 birds from rare species were counted, and an oil spill from EXXON VALDEZ oil tanker brought about the death of 100,000 to 300,000 seagulls and 3500 to 5000 seals.
It's been estimated in oil spilled areas; about 70 years are required for marine life to completely restore.
The destructive effects of oil compounds on open rocky shores are less than those which are within the eyesight.
At first a number of coastal inhabitants die but tides will help to clean the oil off the shore. Animals living in rocky shores will be restored, but it depends on various factors such as amount of oil, effect of waves and temperature.
Decomposition of oil materials is done by bacteria but it's slow, especially in cold waters. If a soluble fertilizer is added to the sea water or sprayed on rocks and sediments it will accelerate the decomposition process.
Experience has shown that in these assisted conditions animals restoration process will begin in a few months, but in natural process it takes one or two years. It has been observed that oil materials in sediments and cavities of sea floor will persist for 15 or more years.
Mangrove forests are one the essential habitats of coastal lines which is greatly affected by water pollution. Their importance is because of the following:
1. The main food production region in coastal habitats
2. The fish and prawn hatchlings spend their infant stage in these forests
3. Preventing shores' erosion
4. Biological filter for coastal regions
5. Marine animals hatchling completely depend upon these forests
The harmful effects of oil spills on mangrove forests:
1. Pneumatophores are covered by oil, preventing the plants from "breathing"
2. Oil will directly smooth and soften some parts of the roots, causing them to suffocate
3. Reduction of light penetration and photosynthesis
4. Solar radiation absorbed by black oil sheens will increase the natural temperate of water
Effects of oil spills on prawn hatcheries
1. Delaying cells divisions
2. Unnatural spawning of parents
3. Mating inhabitation reactions
4. Reduction of feeding activities in parents
5. Obstruction of breathing organs
6. Irritation and disruption in respiratory systems
7. Reduction of prawn quality and their yield in farms and natural habitats
8. Reduction of microfauna on the sea floor as the food of macrofauna such as prawns
Oil pollution will affect the fish reserves on the region, causing them to smell, reducing their commercial value, poisoning fishes and suffocating them because of oil settling on their gills, destroying their hatcheries and disrupting their immune system.
Considering that oil spills move and transports by sea currents, nearby prawn farms will not go unharmed.
Effects of oil pollution on maritime farming complexes
1. Pollution of intake water and mortality caused of poisoning
2. Decreased nutrition value of the intake water
3. Change of smell and taste in prawns and reduced commercial value, making them unable for exports
4. Disturbance in the feeding activities of prawns leading to lower production
5. Irritating immune system, reducing the ability to resist common diseases
Effects of oil spills are not limited to the time of incident. For example oil pollution in the Massachusetts shores 1969 was evident after 7 years on crustaceans of that region. Reports indicated that oil pollution in France by 1969 halved fish sells at the Paris markets.