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In
brackish areas, many of the most noticable and well known Marine specie
are missing. This is true of, for example, large brown algae and many encrusting
algae, aswell as lobsters,
common
crabs, starfish
and green
sea-urchins. Quite often, whole groups of organisms became scarce when
the salt content decreases. Red algae and echinoderms are examples of groups
that have very few representatives in brackish water. Green algae and molluscs
fare better. Where the salt content is more stable, organisms tend to be
more numerous, for example mosses and insects that you normally by lakes
and rivers.
Geography, climate and history
Usually, different conditions prevail in
different
geographical areas and their history can vary greatly. These differences
can be of significance for which organisms that are found on different
beaches. The climate changes from both east to west and from north to
south, thus giving varying light, rain, temperature and ice conditions.
Food resources
and seasonal changes are also different. An example of geographical differences
in a west-east direction is the Norwegian west coast that is open to the
deep and extensive North Atlantic, while the Baltic that is almost totally
enclosed has a minimal and sporadic exchange with the Atlantic. This affects
the water quality and how organisms spread to different areas and establish
themselves.
Another difference between east and west is that during
the last 15 000 years the environment has varied much more along the Norwegian
and Swedish west coasts. During this period, the Baltic had an opening
to the Atlantic, while at other times being totally enclosed.
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