Download Biodiversityreport about the Baltic Sea

Aristotle University of Thessaloniki
Institution of Biology
Maria Lazaridou
Biodiversityreport about the Baltic Sea
and its linking seas
Thessaloniki, March 2000
Jens Henrik Ringsbo
Contents
1.
2.
3.
3.1.
3.2.
3.3.
4.
5.
6.
6.1.
6.2.
6.3.
7.
8.
Introduction
The history of the water cleaning in Sweden
The Baltic sea – its dynamic water convey
The geology of the Baltic Sea, Oeresund and the Danish Baelts
The water influx through Oeresund to the Baltic Sea
The flood of water from the Baltic Sea
Species problems in adaptation
The Baltic Sea – an exposed area
The fish and the breeding in the Baltic sea
The salmon (Salmon salar)
The sea trout (Salmo trutta)
The cod (Gadus Morhua)
Conclusion
References
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1. Introduction
As the most of you probably know, Sweden is situated in the north of Europe. It is
however not that very wellknowned, probably because of our low population, that
Sweden, accounting to the area is the second biggest country of Europe (France is the
biggest). While just parts of Sweden are bordering to other countries, this means that the
Swedish coast is quite long.
The sea and the lake have therefore in all times been a reason for settlement thanks to its
procuring of food to the man. At the same time it has been a good place to throw garbage
and other things that the man has been ill of having in his nearness.
So has it been for a long time and so it still is today. The difference is that we today are
much more aware about the consequences of this dumping. We know that it damage the
sea and its organisms, that we are at a breaking point where action is the only way to
rescue the seas. Many things have also been done, especially by stifting of new laws
based on research, but much is also to be done. As long as the population of the world
remains to increase is the only solution not just to reduce the dumping per person, but
more rational measures must be done. Therefore is it important that people get a
knowledge about what is special with different seas and how they also are affected by
natural changes. A step in this direction is to get some knowledge about the very special
sea that surround the east of Sweden and how it is dependent on the water of the west of
Sweden.
The waters that surround Sweden are the Baltic Sea, the sound Oeresund, Kattegatt and
Skagerakk. The more famous of those is probably the Baltic Sea, while this is the biggest
brackwater sea in the world.
The Baltic Sea is a nearly enclosed sea with the only connection to the westcoast and the
oceans through the narrow and shallow sound by Oeresund and the belts in Denmark.
Because of this the supply of salinic water is limited and therefore the weather and wind
in a high degree controls the changes in the Baltic Sea.
The supply of freshwater on the contrary is very big. From all the countries around the
Baltic Sea falls a great number of watercourses which brings not only freshwater but also
sediment and nutrients which reduces the visibility in the Baltic Sea. Many of those
countries have for a long time supported themselves using agriculture, what have caused
that those materials have been stored in a very long time.
2. The history of the water cleaning in Sweden
After the industrialization in the beginning of the twentieth century many things changed.
People moved from the countryside in to the cities. This lead to major changes and
problems. From being used to that every household having their own outhouse and that
everyone took care of their own waste, now the situation was different.
A sewage system, rainwater system and drinking-water systems had to develop. The
problem was that there didn’t exist a way to clean the water. While direct outlets soon
created attention because of the stench, the littering and the higher risk of infections,
something had to be done. Furthermore the water contained large amounts of nutrients
and soon a great eutrophication of the water areas that had to take the nutrient could be
seen. Therefore, as a first natural measure, the mechanical cleaning came.
It’s principle was really easy: Gratings trapped trash and solid particles were sedimented
to the bottoms in basins. The environmental problems yet remained while high amounts
of nutrients and organical matters still were in the water as dissolved particles.
A more advanced cleaning was therefore required, and in the early fifties so the
biological cleaning came. The biological cleaning works so that microorganisms are
supplied into the water to consume the organic matter. The method is effective – the
sanitary departments can break down approximately 90% of the organic matter, instead
of this taking place in the water outlets.
The biggest villain when it comes to outlets has not been the densely built-up areas but
the industries. Especially the Swedish pulp- and paper industry has contributed to the
outlets, but during the last decades has those outlets been greatly reduced. Despite that
the production of pulp and paper has increased since the sixties, the outlets have been
reduced by over 80%.
This means that the state of oxygen has greatly improved in both lakes and coastal areas,
and many before completely dead bottoms have the flora beginning to come back.
But not even the biological cleaning could completely reduce all the nutrients from the
sewage water. When the households during the sixties started to use phospatebased
detergents, there was directly an increased growth of algaes and other vegetation in the
watercourses observed. Phosphor is namely normally of shortage in freshwater. Every
contribution therefore lead to an increased growth not only in the lakes but also in some
coastal areas with limited water circulation.
Therefore it was a really important step when most of the sanitary departments in Sweden
installed chemical cleaning in the beginning of 1970. The chemical cleaning can
eliminate approximately 90% of the untreated sewage waters phosphor contents. Since
1970 is almost all Swedish densely built-up areas and smaller industries connected to
sanitary departments driven by local government, and nearly 95% of all outlets pass
through biological as well as chemical cleaning. This makes Sweden, together with
Finland have the worlds best developed sewage water cleaning.
The sewage cleaning has rarely been able to prove any large-scale improvements. A
reason can be an increased population and an industrial expansion. On the other hand
clear improvements have been seen in lakes and archipelagos.
As mentioned earlier the Swedish agriculture has contributed with large amounts of
nutrients to lakes and coasts. From 1920 to 1970 the phosphor manure of the fields
doubled. Today the level has gone back to what it was 1920, but the amount that already
is stored in the ground is still unreduced. In the lakes the same problem is to be seen.
Even if the outlets are reduced, there will always be leaking from the bottom sediment in
the lakes, where the phosphor is accumulated.
Today is it, however, outlets of nitrogen content market manure that provide the biggest
problem. On divergence to the phosphor the nitrogen contents are more easily absorbed
in the ground and the crops are rarely able to take up all nitrogen manure before it has
passed the roots and down in the soil. From the soil it later leaks out to the groundwater
as well as watercourses – and from there to the sea. (Overgodning – Naturvardsverket)
3. The Baltic Sea – its dynamic water convey
The Baltic Sea is a proportionately small sea (see picture below) that maybe doesn’t
affect people that don’t live in its vincinity. It is yet an important sea, not only because it
provides coast for 9 countries, but also because it shows organisms that have endured big
changes and high stress
moments during the centuries.
This due to the Baltic Sea
being a brackwatersea, as a
matter of fact the biggest of
the world. Moreover it’s a
shallow sea that has limited
contact with other seas, and
therefore has a so slow
renewal of the water of 30
year. This geography makes
the sea a mirror of how the
man and her activities can
affect the environment.
(Overgodn. Naturvardsverket)
Picture: Scandinavia with
surrounding water.
(Claes Bernes, 1999)
A great part of the water of the Baltic Sea comes from many of the rivers that fall into the
coasts. Furthermore salt water rushes in through the belts and Oeresund. The freshwater
lays itself on the surface, and there is a clear dividing line between the freshwater surface
water and salt bottom water which means that the entire water doesn’t mix very well. We
are going to come back to this, but first it’s important to understand the geology of not
only the Baltic Sea, but also of Oeresund.
3.1. The geology of the Baltic Sea, Oeresund and the Danish Baelts
A deepmap shows that the Baltic Sea roughly can be divided into three basins. The first
basin creates the Real Baltic Sea with deep sea trenches outside the islands of Bornholm
and Gotland. Deepest is Landsortsdjupet with 459m, but the average depth in the Real
Baltic Sea is only 60m.
Northward by the sea of Aland, the Baltic Sea starts to shallow up again, to create the
next basin, the Bothnian Sea.
Finally it gets shallow again near Umea, which provides a border to the next basin, the
gulf of Bothnia.
Whit regards to the belts and Oeresund (see picture below), those provide the only
approach for salt water. Out of a topographic view, Oeresunds upper limits are drawn
between Gilleje(Den) and Kullen(Swe) and the lower limits between Stevns(Den) and
Falsterbo(Swe). ( Skanes Naturvardsforbund – Oresundsbron…)
Those limits make the sound 100km long, with a width of a little more than 20km in the
both mouths. The most narrow place, between Helsingoer(Den) and Helsingborg(Swe), is
only 3km in width and provide one of the two essential resistance for watertransport.
Picture: Oeresund, between Sweden and Denmark, and the 2 Danish belts.
(Mkartan 1974)
The other resistance, the souther, provides of a threshold between Dragoer(Den) and
Limhamn(Swe). Through it goes two deeper trenches, Drogden in the west and
Flintrannan in the east. The trenches have a minimum depth of 7m.
The waist in the north and the threshold in the south creates a basin, the Oeresundbasin,
which has an average depth of 15m.
In Stora Baelt (the belt) there is a 22-25m deep trench that goes the whole way to
Darstroskeln between the German coast and Falster(Den). The trench has the depth of
18m.
Through the belts (there is also a smaller one, called Lilla Baelt) flows brackish water (78‰ of salt) from the Baltic Sea northward. This water goes as a surface stream over the
salt (30-34‰) south going water from Kattegatt. There takes place a stirring of those by,
as it is called, Baeltfronten, and also in some extents in Oeresund, but mostly the salt and
brackish water separated and the transition is marked by a halocline, that in the
Oeresundbasin is at a depth of 10-20m. The salt content varies therefore from place to
place and depth to depth.
The water circulation is rapid, with a changing of all water in just a couple of days. If you
look at the bottom stream the Baltic Sea is given 70% of its salt water from Stora Baelt,
the rest comes through Oeresund. But in return it is the most salty water that goes through
Oeresund.
On the basis of a year, in average 900km3 brackish water flows from the Baltic Sea to
Kattegatt, while the Baltic Sea only gets half of this figure, 450km3.
The surface stream can change, but is mainly north going (60%). Stream calm reigns 4%
of the year.
South directed surface streams are connected with westerly wind directions, while the
most powerful, the north directed surface stream, is connected with easterly wind
directions.
The earth rotation turns the surface stream in the north of Oeresund faintly to the east,
therefore the salt content is higher on the Danish side than on the Swedish. The different
wind directions create different problems, which are important to understand. (Oresund,
ett strommande vatten)
3.2. The Water influx through Oeresund to the Baltic Sea
Normally the water is transported into Oeresund with the northwest wind on the back of a
passing low pressure. When the wind reaches gale force and remains so for several days,
the water level in the southern Oeresund rises rapidly with up to 1m above the normal
water level and all lowland around, for an example the peninsula of Falsterbo(Swe),
floods. But the real extreme floods don’t seem to be started from this direction. This is
being due to that the sound is too narrow up in the north and too open down in the south,
and with that the Baltic Sea is able to swallow the most of the coming water. (Oresund,
ett stommande vatten)
3.3. The flood from the Baltic Sea
Also when it regards to the flood from the east, it is one or more low pressure that is the
cause. What happens is that westly winds during a longer time have pressed up big
amounts of water up to the Bothnian Sea and to the Gulf of Finland. When then a low
pressure breaks through and the wind in the worst case becomes northeasterly or north
northeasterly, big amounts of water is pressed down to the south of the Baltic Sea and up
into Oeresund, a way that rapidly becomes narrow between Helsingoer and Helsingborg.
On the peak of the southwest of Sweden – Skanoer/Falsterbo water is rushing over the
channel of Falsterbo.
Closely to the coast of Oeresund moves a strongly eroding and dangerous north directed
stream. Streams like this create high water levels on different places as in
Travemunde(Ger) and Skanoer/Falsterbo, where the water level can rise with 2 to 3m.
This causes a special environment for both birds (waders) and marine organisms.
(Oresund, ett strommande vatten)
4. Species problems in adaptation
As mentioned earlier salt water streams into the Baltic Sea only through Oeresund and
the Danish belts. This water, that has a salt content of 30‰ lays itself in the trenches of
the Baltic Sea.
The lighter freshwater that comes from the rain and all the rivers, lays itself as a 70m
huge lid over the considerably salter and heavier deepwater.
The boundary between the freshwater and the salt water is relative sharp and is called
halocline. The water exchange between the layers is rare.
The Baltic Sea exist accordingly of a freshwater surface sea and a more salter bottom
sea. This, of course, causes problem for plants and animals that have adapted to live
either in salt marine water or in freshwater of lakes and watercourses.
Ever since the glacial period the Baltic Sea has several times changed between being a
sea and a lake. The last transition was for 7000 years ago, when the lake became sea, but
it may now go back to being lake again. The stage of brackish water that the Baltic sea
now turns out to be, is slightly more than 2000 years old.
Some animal species have succeeded to survive the physical and chemical revolutions
during the history of the Baltic Sea. Those are
called glacial relics (see picture) and examples
among them are Opossum shrimp (Mysis
relicta), (Monoporeia affinis) and (Triglopsis
quadricornis). It’s actually incredible when you
think a while, that those animals have lived here
since the glacial period.
Picture: Triglopsis quadricornis (Sven Halling 1998)
For other animals it has been much harder. Only a few plants and animals species have
had the time to adapt to the low salt content in the Baltic Sea.
The marine species have had to adapt their contents of bodysalt after the surrounding
water. The reason for this is that their bodies are comparatively more salty than the
surrounding water and that the bodies by osmosis tries to level out this. This threatens to
burst the bodies and only the species that can protect themselves against this can survive
in the Baltic Sea. To hold the water out cost energy, which results in that most of the
marine species become much smaller than their sisters on the west coast.
For the freshwater species the same thing happens but instead of bursting they shrivel up
because they lack water in the body.
The bigger the distinction in salt content it is, compared
with the natural, original surrounding, the harder the
species get to adapt to prevailing salt content. Studies
have shown that the number of species is as lowest by salt
content around 6-8‰. With this salt content occurs
almost no species of either marine or freshwater. As to be
seen in the picture to the right, the salt content decreases
rapidly from Skagerack and counterclockwise up to the
Gulf of Bothnia, and almost the whole Baltic Sea has the
salt content mentioned above (6-8‰). (Oresunsdbron –
Skanes Naturvardsforbund)
Picture: Map of salt content in the seas that surround
Sweden (Claes Bernes 1998)
The number of marine species decreases from south to north in the Baltic Sea. In
Oeresund and the Danish belts occurs the big decline of plants and animals. Most of the
marine species disappear, for an example all echinodermas (sea stars and sea urchins).
The blue mussel (Mytilus edulis) and the Malcoma balthica are yet found all the way up
to the Bothnian Sea.
The blue mussel (see picture to the left), that just
becomes 1/3 of the size it has at the westcoast,
form big banks to a depth of 30m and is from the
point of view of the weight the most abundant
species of the invertebrates.
Picture: The blue mussel (Mytilus edulis)
(Richard Koppel 1998)
Salt water fishes as Baltic herring (Clupea harengus) and sprat (Sprattus sprattus) are
common in the whole Baltic Sea. Cod survives in the Bothnian Sea but the spawning
does only succeed in the more salt waters in the trenches of the Real Baltic Sea. In the
coastal areas, in the Bothnian Sea and in the Gulf of Bothnia are freshwater fishes as pike
(Esax lucius), perch (Perca fluviatilis) and roach (Rutilus rutilus) common.
More northward, in the Real Baltic Sea, the number of species are sparse, but it’s by the
threshold to the Bothnian Sea that next big decline occurs.
In the Bothnian Sea we find the most extreme environment of the Baltic Sea – purer
freshwater, of low nutrition and food value and with long icy winters. Not many species
are able to live here.
No bladder wrack (Fucus vesiculosus), which usually is found
in the whole Baltic Sea (see picture), is found here. Instead
are big plants represented by stonewarts (Characeae) or
freshwater plants as pondweed (Potagometonaceae) and
spiked water milfoil (Myriophyllum spicatum).
While the blue mussel don’t survive in the low salt content,
the breaking down of organic matter and the reclaim becomes
less effective. In shallow water lives freshwater animal as the
small mollusc Theodoxus fluviatus, pea mussel (Pisidium)
and larvae from midge larvae (Chironomidae) and caddisflies
(Trichoptera).
Picture: Bladder wrack (Fucus vesiculosus) (Hans Kautsky 1998)
As mentioned above there is on the contrary to the westcoast, no echinoderma to be
found. Other animals that you can find on the westcoast but not in the Baltic Sea are
Ascidiaccea, corals, sponges; brown algaes as Halidrys siliquosa, Ascophyllum nodosum
and Laminaria.
That those species not are present in the Baltic Sea also means that species associated
with them are not to be found.
It is therefore not hard to realise that the marine and the freshwater species lives on a
brittle thread. If more stress moment is added like pollution or global environmental
changes, this will affect not only a single species but probably the whole ecosystem.
Some scientists think that the Baltic Sea, with its few number of species, is more
vulnerable than Skagerrakk/Kattegatt. They point on that there are a few species with
overlapping manner of living, that belong to the same functional group. For an example
we can take the blue mussel: The blue mussel is the only bigger hard bottom species that
live of filtering plankton and organic particles from the water. Loss of blue mussel can
give big consequences for the ecosystem of the Baltic Sea, while the function of the
individual species not can be overtaken by any other. (Biologisk mangfald… - N. verket)
5. The Baltic Sea – an exposed area
The nature has its progress and is the whole time changing. But the last hundreds of years
has the man made the big changes. This has lead to that the Baltic Sea is one of the most
polluted sea areas in the world, hard affected by eutrofication, environmental toxics and
oil spillage. Furthermore man has introduced at least 30 new species in the Baltic Sea,
with yet unknown consequences for the ecosystem. Examples of those species are
Canadian waterweed (Elodea canadensis), zebra mussel (Dreissena polymorpha) and
Marenzelleria viridis. With the slow water renewal of 30 years, the major parts of the
pollutions stay in the Baltic Sea. The loss of a tide also contribute to that it takes that very
long time for the pollutions to dilute. The only true dilution takes place when the
weathergods settles in their winds (see above). Then is also new oxygenrich water
brought in, something that is of real importance for the Baltic Sea. Since some decades
big parts of the deep areas of the Real Baltic Sea have a lack of oxygen. This depends,
above all, on that the supplying of oxygenrich bottom water throw Oeresund and the
Danish belts is too small, but also on that the oxygen consumption has increased because
of the eutrophication. The oxygen consumption knocks out bottom living animals and
make, for an example, it more difficult for the breeding of the cod.
Another problem is the spillage of oil. Illegal oil spillage every year kills thousands of the
birds of the Baltic Sea. Even more damage is done by the oil that trickles out from
marinas, the rainwater systems of the cities and from smoke from chimneys and the
exhausts of cars.
A third problem is environmental toxics as PCB and DDT. Those have decimated the
existence of grey seal, otter and European sea eagle, even if it since the seventies has
occurred a significant decrease of those toxics and with that an improved breeding. Also
chlorine organic compounds have created big problems and apprehend to be of important
for the M74 disease, that causes high mortality among the fries of the Baltic Sea (see
below). (Biologisk mangfald i havet – Naturvardsverket)
6. The fish and the breeding in the Baltic Sea
There is, despite the above written problems, a lot of fish species in the Baltic Sea. Three
of the more important, maybe from the viewpoint of consumption by man, are the
salmon, the sea trout and the cod. Success and adversities for the fishing of those is
closely related to the capability of breeding. If the breeding is successful this leads to a
retaining biodiversity. For the salmon, the sea trout and the cod the breeding is yet in
danger.
6.1. The salmon (Salmon salar)
The wild salmon of the Baltic Sea starts its life amongst the stones in the bottoms of
rivers with rapid streams. Among all the salmon thrives in watercourses of the Gulf of
Bothnia, but there is also some in the Gulf of Riga (Lat), the Gulf of Finland and several
in the south of Sweden.
The adult salmon migrates up in the rivers to spawn, and during October and November
the females lays their roe. The roe then fertilizes by the milt of the male fishes. During
the winter the fertilized eggs lie under the stones of the watercourses and they then hatch
when the spring comes. The new hatched fish larvae stays in the spawning ground and
feed on the yolk-sac. The yolk-sac is corresponding to the yolk of the egg of a hen.
After a month the yolk-sac fries leave their nest(?) and looks for a sheltered place where
it can grow by catching swimming insects and other smaller animals.
The now small fries defend their territory at the same time they are growing. When they
have grown enough their metabolism, appearance and behavior changes. This happens so
that they will be able to stand the migration to the sea. The time it takes for the fries to
come to this state varies from 1-2 years in the rivers of the south of Sweden up to 4 years
in the north of Sweden. The migration starts when the temperature reaches 10ºC. Once
there, they have to eat, grow and reach sexual maturity. The food constitutes of sprat,
Baltic herring and also of stickleback and Ammodytes lacea
After 1-3 years in the sea the salmon returns to the river where it was born. It readjusts
itself again to freshwater and starts to spawn. The same salmon spawn several seasons
but is often caught before.
Salmon cultivation are very common in Sweden and Finland, but also in the other
countries around the Baltic Sea. This is due to, in Sweden, while the power plant
companies expanded the hydroelectric power they had to feed up salmon fries while the
changes for the breeding in natural way changed.
To feed up fishes in cultivation has brought along problems. While so huge amounts of
fish are in a small, limited area, the risks for fungus- and parasite infections getting a hold
increases. There is therefore strict rules and continues controls of the cultivations.
It was by a cultivation like that, that a new disease was found in the beginning of the
seventies. What was seen was that a lot of the yolk-sac fries died without any reasonable
explanations. Immediately scientists suspected the environmental toxics, and by
cultivations around Sweden, they could see that many of the watercourses around
Sweden were contracted. They gave the disease the
name M74, M for environmental and 74 for the year
of the discovery.
The disease is connected to some salmon females,
and among the litters that are infected, almost all fry
dies. The disease appears when the fries are some
weeks old. They get a darker body color than
healthy fries and they move uncontrolled.
Picture: The salmon fry – look at the color and the
Yolk-sac (Jenny Lundstrom 1999)
The heartbeat slower and at a closer look it can be seen that there is a white precipitate in
the yolk-sac. In the final stage the fries are very slow and they have got protruding eyes.
When you dissect a fry with symptom ofM74, you can see that some cells in the brain
have died. The metabolism of the fries is worse and the muscles have been emptied on
the energy reserves of glycogen.
You can also see by the way the
female swims if the fries will have
M74, but most clearly is it to be seen
in the roe. Roe that will lead to M74
contracted fries is faintly orange while
it normally is red-orange (see picture).
The color is due to the amount of
carotenoids. Those have an important
cleaner function in biological systems
while they caught aggressive atoms of
oxygen that otherwise would damage
the cells. The amount of carotenoids
Picture: The salmon Roe (Knut M. Svensson 1979)
is lower in females with M74.
It is now known that a part of the disease is due to lack of thiamine. But still there is no
answer on why the salmon has a lack of thiamine. (Fisken och fortplantninget i Ostersjon
– Naturvardsverket)
6.2. The sea trout (Salmo trutta)
Also the sea trout can be affected by M74, but the disease is not as widely spread as by
the salmon. This can be due to the sea trout getting more varied food and then also more
thiamine and carotenoids. Another cause can be that the sea trout don’t leave the coastal
area. They therefore don’t need to use their reserves.
The sea trout is otherwise related to the salmon, but have partially different eating habits.
They feed above all on fish, for an example Baltic herring, but also on different
invertebrates. (Fisken och fortplantningen i Ostersjon – Naturvardsverket)
6.3. The Cod (Gadus Morhua)
The cod lives in the Baltic Sea on the margin of its normal spreading area. It breeds
successfully only in the Real Baltic Sea. However, it can happen that cods can swim all
the way up to the Gulf of Bothnia, but there has never been found any fertilized eggs that
far north.
The reason for this is that the eggs of the cod have to float freely in the water, which isn’t
possible with the low salt content of the northern Baltic Sea. In the salt water of the
westcoast the natural floating makes that they get closely to the surface, while those in
the Baltic Sea have been forced down to depths where the salt content can bear the eggs.
This result in that that the cod only breeds well in the depths of Bornholm, Gotland and
Gdansk.
The population of cod in the Baltic Sea has been strongly reduced during the last years.
This is due to too much fishing, but also because of a lack of oxygen. The oxygen
conditions are closely related with the weather, and so also is the population of cods, and
there is to be seen clear connections in the population of cods and years when strong
winds have carried oxygen rich water from the sounds up into the Baltic Sea.
A big problem for the population of cods has been the eutrophication that further has
reduced the population.
Too much fishing of cods during the beginning of the eighties has changed the ecosystem
of the cod. Normally the cod controls the supply of Baltic herring and sprat, while the cod
is the only important fish of prey in the top of nutritive chain of the Baltic Sea.
Now the case is the opposite, while the egg and larvae has become food for the fry state
of the two fishes.
However, it doesn’t seem that the cod have been disturbed by environmental toxics and
they have not shown any signs of M74. (Fisken och fortplantningen i Ostersjon –
Naturvardsverket)
7. Conclusion
All this shows us that the sea is vulnerable. The nature itself makes big changes, and
maybe that is the way it should be and has to be.
But when man makes changes, they are much faster. The ecosystem doesn’t get any time
to cope with the changes, and species from both plant and animal may disappear forever
before we gat a chance to rescue them.
The Baltic Sea shows both of those things. This makes it to a very important sea to study.
But we have to be careful so there will be something left to study.
8. References:
Temafakta: Biologisk mangfald i havet, Naturvardsverket
p.10,11
Temafakta: Fisken och fortplantningen i Ostersjon, Naturvardsverket
p.13,14
Oeresund - ett strommande vatten, http://home1.swipnet.se
p.7,8
Oeresundsbron – en onaturlig hagring, Skanes Naturvardsforbund
p.9
Overgodning, Naturvardsverket – http://www.environ.se
p.5
Pictures:
Bernes Claes, Fisken och fortplantningen i Ostersjon, Naturvardsverket, Mars 1999 – p.5
Bernes Claes, Biologisk mangfald i havet, Naturvardsverket, September 1998 – p.9
Halling Sven, Biologisk mangfald i havet, Naturvardsverket, September 1998 – p.8
Kautsky Hans, Biologisk mangfald i havet, Naturvardsverket, September 1998 – p.10
Koppel Richard, Biologisk mangfald i havet, Naturvardsverket, September 1998 – p.9
Lundstrom Jenny, Fisken och fortplantningen i Ostersjon, Naturvardsverket, Mars 1999 –
p.12
Rabe’n & Sjogren, Mkartan over Sverige, 1974 – p.6
Svensson Knut M., Fisken och fortplantningen i Ostersjon, Naturvardsverket, Mars 1999
- p.13