The environmental problems in the Black Sea – present and future

D.N. Kozhuharov, Bulgarian Biodiversity Foundation, 2013


1.General   information about Black Sea

The Black Sea is an enclosed sea that is almost fully isolated from the World Ocean and is surrounded by land around nearly all of its sides. His only connection to other water bodies is through Bosphorus Strait, 35 km long narrow natural canal that separates the Black Sea from the Sea of Marmara that binds the Black Sea with Mediterranean Sea through the Dardanelles. Thus, the Black Sea has limited exchange with other seas and much of its flowing waters remain in his basin unable to drain out or mix with waters from other water bodies.

Its catchment area reaches 2.5 million square kilometers and includes 21 countries in Europe and Asia Minor. About 300 rivers annually flow about 350 cubic kilometers of fresh water into the Black Sea. Just to compare, we will mention that 1 cubic kilometer of water equals to 500,000 Olympic-sized swimming pools! On the other hand the analysis of the water balance of the Black Sea (income over cost) shows that the income of the fresh water exceed the cost of salt water with about 1.5 cubic km per year. This fact determines almost twice lower salinity of the Black Sea compared to the Mediterranean and the World Ocean (17 ‰ salinity in the Black Sea, 37 ‰ in the Mediterranean and 35 ‰ in the Oceans). Another feature of the Black sea is that comparing with the Mediterranean, the temperature of the water is lower, especially during winter time. Finally, it should be noted the well-known fact about the poisonous gas hydrogen sulfide presence and the absence of oxygen below 150 m of depth in the waters of the Black Sea. All these factors hinder the penetration and adaptation of Mediterranean fish and plants in the Black Sea altogether. For example, from some 579 fish species in the Mediterranean Sea, the Black Sea accommodates only 144 species. By adding another 24 fish species living also in freshwater and brackish pools (such as sturgeon species), we get a total number of 168 fish species that inhabit and live in the Black Sea. The same applies to other species such as mollusks, echinoderms and others.

Quantity of fish caught per unit of water area, using one hectare as an example area, is known as the “fish productivity of the respective sea”. The fish productivity in the Black Sea during the 60’s of the last century is 5 kg / ha,  in the early 80s due to the increased catch of the European Anchovy and Sprat it reached up to 16 kg / ha to fall to 2.2 kg / ha during the late 80s. The reasons for this are of anthropogenic origin, i.e. due to human activity.


2.The Black Sea as an ecosystem

Black Sea is a complete and unified ecosystem consisting of several ecosystems of lower rank. It works as follows: the approx. 300 rivers that flow into the Black sea supply biogens, i.e. salts of nitrogen, phosphorus and other essential minerals for the plants. Based on them and using sunlight algae and sea grasses grow. With them are fed  herbivores marine animals and they themselves provide food for predatory invertebrates and fish. The fish in turn become food for birds and dolphins. After the death of plants and animals, their tissues are decomposed by heterotrophic bacteria. As a result of this digestion the organics are converted into inorganic substances – nitrates, phosphates, etc. which are used by the plants. So the circle closes and begins again with a new life cycle. All species diversity in the Black Sea can be reduced to four life forms. Benthos is the scientific name of the seabed inhabitants, planktons are the organisms that live in the water column, neustons are the organisms that float on the top of the water or live right under the water surface and nektons are the actively swimming organisms such as fish and dolphins.

Benthos are divided into bottom plants known as phytobentos and bottom animals known as zoobenthos. Plankton is also divided in accordance to whether it comes to plants or animals to phytoplakton and zooplankton. The same is true for the neuston. According to its habitat the fish can be divided into pelagic fish, i.e. those that are located far from the bottom and demersal fish that lives on or near the bottom of a body of water.


3.The Black Sea-sea under threat

In the northwestern region of the Black Sea is a vast area of shallow water known as the Northwest Shelf that covers the area of 100,000 square kilometers. This region that borders the coast of Ukraine, Romania and part of Bulgaria was inhabited by a great variety of most species living in the Black Sea until recently. The reason for this is that the shelf biodiversity is always greater than the one in the deep parts of the sea. Also that in this vast area are the flowing waters of the three largest coastal rivers – the Danube, Dnieper and Dniester. In the central part of this shelf at a depth of 20-50 m the world’s largest population of Phyllophora algae was discovered in 1908. The area occupied by this red algae bears the name of its founder and is thus known as the ” Zernov’s Phyllophora Field “. This algae is used by humans for the production of agar – a gelatin -like ingredient in the ice cream. This region covers an area equal to the area of the Netherlands and Belgium accommodated not only the Phyllophora algae but it formed a unique ecosystem of plants and animals altogether. Unfortunately, all this is now in the past and the ecosystem of the Northwestern shelf has died off forever. The reason for this is the eutrophication or over-fertilization. In the 60s years of the last century, the catchment basin countries have begun to apply intensive usage of agricultural and livestock fertilizers. As a result, excessive amounts of biogenic waste has entered the rivers and thus fell directly into the Black Sea. As a consequence the number and biomass of phytoplankton increased.

The increased mass of phytoplankton lead to shading of the light and to decreasing of its transparency – from 10-20 m in the 1950s the waters transparency drop to 1-8 m in 1980’s. In this way the bottom algae that lived at a depth of more than 5-10 m began to die. Due to the decomposing organic matter and related bacteria that used up more and more oxygen, the total amount of oxygen severely decreased. Thus the whole bottom flora died due to lack of oxygen. From the whole ” Zernov’s Phyllophora Field ” very small area remained alive and the Phyllophora algae lost its importance as a source of raw material for the food industry.

After the vegetation, the phytoplankton settled to the bottom. But if in the 50s years on 1 square m of Northwestern shelf deposition was around 1 gram of phytoplankton, then in the 1980’s already deposited around 36 grams. This increased decomposing mass of microalgae consumes a large amount of oxygen dissolved in the water. This leads to oxygen deficiency or hypoxia, that brings to mass death of zoobenthos and demersal fish in large areas, a phenomenon known as “Zamora”. It is estimated that in the period 1973-1990, a  60 million tons of bottom inhabitants died of hypoxia, of which we count 5 million tons of fish.

In the early 90’s a decreasing of the “bloom” of phytoplankton has been found and thereby the areas with hypoxia have been reduced. The reason for this “renewal phenomena” is the reduced release of biogenic waste in the upper reaches of the Danube and the economic downturn in the countries along the lower reaches of the river. Restoration of natural wetlands is another effective tool for the removal of the biogenic waste. This brings hope in possibility of creating an environment for new species and for protecting the region from flooding.


4.The invasion of the invaders

Ships that travel without cargo fill their containers with ballast waters for greater sustainability. When filling, various marine organisms and sediments are sucked into the pump. If the temperature, chemical composition and the duration of the voyage are with accordance with the living conditions of organisms some of them may survive the journey and reach the end point of the vessel. After pumping and the separation of waste and ballast waters, some of the organisms fall into a new and unknown to them sea. If conditions permit, they may survive and reproduce in this new home. They can also migrate through the hull of the ships where various algae, shellfish, crustaceans or their spores, eggs or larvae are attached. So these “free- ticket” travelers may enter into new territory where they can reproduce and develop successfully. Most recent regional inventory of alien species in the Black Sea lists over 200 alien species brought in from all regions of the World Ocean and only few of them are actual invasive species. Under the invasive species we mean those species which have a harmful effect on the local flora and fauna simultaneously adversely affecting human activity. At the same time it should be mentioned that certain species have a positive effect on the human activity and on humans in particular.

Sea-snail Rapana thomasiana is a classic example of an invasive species introduced from the Far East and in particular from the Sea of Japan. The first time it was discovered in the Gulf of Novorossiysk in 1947. Due to the lack of natural enemies, such as Starfish the population of Rapana increased dramatically and caused a great harm to the fauna of the Black Sea. This predatory snail that eats oysters, mussels and other bivalve mollusks now greatly reduces populations of the black mussels. Black mussels as is known is a natural biofilter of the sea and they play an important role in the purification and filtration of water. Thus in the formation of primary production, i.e. the phytoplankton, that is used for the formation of zooplankton or the so –called “cycle of secondary production”- the basis of food base of fish, is impaired. Thus, the increased population of Rapana inevitably leads to significant changes in the ecosystem of the Black Sea.

In the early 1980’s the Black Sea has found the presence of other invasive species Mnemiopsis leidyi, a type of comb jelly. This externally beautiful exotic representative of the marine flora coming from the Atlantic coast of North America is actually the most dangerous and harmful invader that has ever arrived in the Black Sea waters. This representative of Ctenophora or comb jelly does not have any natural enemies so its population has increased dramatically. By the end of the 80s years it has reached the impressive number of 800 million tons for the whole Black Sea basin. It feeds on fish larvae and zooplankton that is the food base for various species of fish and at the first place of European Anchovy. So the explosive growth of the population of Mnemiopsis has led to a catastrophic decline in fish catches in the Black and Azov Seas in the late 1980’s. Thus in the early 90’s Anchovy fishery declined sharply to 60,000 tons. According to the experts of FAO (United Nations Food and Agriculture Organisation) losses from the decline in fish catches are estimated at about 240 million dollars per year. This is a typical example of invasive alien species, which on one side has a negative impact on the marine ecosystem and on the other has a negative effect on certain types of human activity. Despite the continued presence of Mnemiopsis in the Black sea currently the stocks of Anchovy have recovered but the stocks of other species remains reduced.


5. Other dangerous practices

Bottom trawling is another kind of human intervention with detrimental consequences for the Black Sea ecosystem. This type of fishing practices were banned in the early 20th century because of the damage they cause to the benthic fauna and flora. But in the early 1970’s, all Black Sea countries resumed bottom trawling in order to increase fish production and in particular the catches of sprat. According to official Soviet data sprat production reached 340,000 tons for a period of about 10 years and the main part of it is caught by bottom trawling in the northwestern part of the Black sea.

European anchovy and sprat are the main fish species inhabiting the Black Sea basin that are of interest for industrial fishing. The major source of sprat are concentrated in the bottom layer and therefore it was decided to carry out fishing with bottom trawls. To enable the trawl position to lie as close as possible at the seabed and to plow from there, special ballast rollers and boards are used. These rollers and boards plow the bottom ground and what does not fall into the trawl is just crushed under the weight of the ballast. This is the way the benthic communities such as fish, some marine animals and mussels -the most important filters of water and the food base of sturgeon fishes – are destroyed. But the most serious negative consequence of trawling is the absorption and dispersion of large amounts of sediment particles from the bottom. The lifting of this sludge and its dispersal at a distance of tens of kilometers leads to a decline in water transparency. This has disastrous consequences for the populations of algae in the coastal zone since over 10 meters depth there is not enough light for any photosynthesis and the algae dies. Further destructions of trawling leads to an increased amount of organic waste and ultimately it leads to the reduction of dissolved oxygen in sea water. The bottom trawl plows a strip 10-12 km long per hour. The lifted cloud of sediment particles however causes a damage and destruction to mussels on an area tenfold of the amount of the plowed strip. The scientific research made in the Black Sea in the early 1990′s showed that in an area, affected by bottom trawling, the biodiversity has shrunk by 71%, the numbers by 60% and the biomass by 95 %.


  1. Black      Sea – hopes and future

Are there any solutions that would maintain the rates of economic growth in the region on the one hand and on another will preserve and protect the ecological balance and biodiversity in the Black Sea? Yes, there are, although this may seem an incompatible combination of two contradictory tendencies at first. The priority task is to reduce the rate of eutrophication of the sea that can be done primarily by reducing the leakage of biogenic materials in the rivers of the catchment area. Second priority is to increase the catches of marine plants and animals consuming nitrate, phosphate and other products of eutrophication. Purification of the drinking and industrial waters and the application of new and safe technologies in the production of detergents and fertilizers is the right way that leads to the solution of the problem of eutrophication. European countries of the Rhine basin have given positive examples. They have managed to lower the amount of phosphates in the river by 50% in the past 15 years. This has had an extremely positive effect on the ecology of the region. So the waters of the Rhine will bring again salmon and other fish species – that were considered missing for decades.

Catches of marine animals that helps to reduce the rate of eutrophication is another useful method, although not as effective as reducing the inflow of biogenic material in the Black Sea. The latter  method is of a more local importance. For example, for the period 1985-1988, Turkey has caught and exported to Japan nearly 3,000 tons of Rapana. This reduced the population of the alien invasive species and also reduced the rate of eutrophication. Simultaneously the catch brought tangible and financial benefits. In 1991, The International Maritime Organization (IMO) adopted a special resolution to prevent the introduction of invasive alien species. According to it, on the board of the ships, as a ballast, only clean water is allowed to be used. The resolution also recommends that in the case of absence of biological control on the ship, the replacement of ballast water can only be done in the deep waters of the oceans. Another recommendation is addressed to the method of treatment of ballast waters with different contaminating chemicals, high temperature, ultraviolet rays etc. Special attention is given to the training of the crew to work with ballast waters and the responsibility of the captain of the vessel is raised. After the comb jelly Mnemiopsis  leidyi another foreign representative of this Phylum enters the Black Sea, named the comb jelly Beroe cucumis but what feeds on  Mnemiopsis. Thus the number of Mnemiopsis begins  to decline significantly. This has  happened only 10 years after unimpeded entry and widespread proliferation of Mnemiopsis.

In Bulgaria The Law on Fisheries and Aquaculture   prohibits  the use of bottom trawls. But with the amendments to The Law as in force from 03.08.2012  in exception of already implemented prohibitions on the use of bottom trawling is introduced a regulated  ability to use a   beam trawls.  Beam trawling will be allowed only in a certain areas of the coast to assess the damage caused by it. The objective is that within a specified period of time in these authorized areas  the fishers of rapana  can to “work”. A survey then will be conducted with an aim to establish if there is any destruction on the shelf structure and there is any negative impact on fish stocks. This will be carried out as a periodic exploitation in various areas of the Black Sea.

Another possibility for the preservation and conservation of biodiversity in the Black Sea is through protected areas by Natura 2000 – a network of special areas of conservation established under the Habitats Directive of 1992. The aim of the network is to ensure the preservation of the most valuable and endangered species and their natural habitats. In the Bulgarian aquatory of the Black sea 6 of these protected areas with 20 m depth are established. It is envisioned that these protected areas are going to be extended to 75 m depth to ensure better coverage of mussel banks as biological reefs. This will also be undertaken for a better coverage of the two cetacean species that are subject of protection – the Bottlenose Dolphin and Harbour Tortoise.  Furthermore, a proposal has been made that three newly protected areas need to be included in the Marine Network Natura 2000. The proposal has been approved by the Bulgarian National Biodiversity Council during late 2012  and the coordination procedures among the state insitutions in charge have started.



1.Zaitsev, Yu.P., Chernoe more: Sostoyanie ekosistemy I puti ego uluchshenia (The Black Sea: Ecosystem Status and ways to improve it), Odessa, 2000 (in Russian)

2. Mee, L.D., Kak da spasim Cheno more- vasheto rakovodstvo za Strategicheskia plan za deistvie za Cherno more (How to save the Black Sea – a popular version of the  Strategic Action Plan for the Black Sea), Varna, 2001 (in Bulgarian)

3. Interview with Valentina Todorova, PhD, Institute of Oceanology, BAS, Varna (in Bulgarian)