l38
W. Schramm
forms occurs in the Arcona Sea, the transition zone from the Western
Baltic to the Baltic proper, the latter being characterized by rather stable
salinities between 8 to 5 PSU, in contrast to the areas west of the Arcona
Sea with salinities changing between 10 to 20 PSU. Finally, a third critical
boundary can be observed in the Aland Sea, at the entrance to the
innermost parts of the Baltic, the Bothnian and Finnish gulfs, where
salinity decreases below 5 PSU down to 2-3 PSU.
Besides salinity, the substrate conditions in the Baltic determine to a
great extent type and distribution of the macrophytobenthos. Great parts
of the coasts of Denmark, Germany, Poland and eastern Baltic countries
consist of sandy or muddy soft bottoms which are only suitable for
growth of rooting plants. Hard substrates necessary for attachment of
seaweeds occur in the form of solid rock mainly along the Swedish and
Finnish coasts, or as glacial materials, particularly along sand cliffs,
which are common along the coasts of Denmark, Germany and partly
also of Poland.
The physiognomically important phytobenthic communities include
the mostly filamentous annual forms in the lower level of the "eulittoral",
followed further down by the Fucus belt and seagrass meadows, and the
red algal communities down to the distribution limits of the sublittoral.
Among these, the Fucus communities are most conspicuous. Fucus vesiculosus, the structurally most important seaweed in the Baltic, forms
together with about 30 species of associated macrofauna and macrophytes the most diverse benthic subsystem, important as spawning and
breeding grounds and shelter for many macrofauna and fish species
(Segerstraale 1944).
In fully marine areas, Fucus vesiculosus and Fucus serratus are usually
intertidal species, forming rather narrow belts as can still be observed on
the west coast of Sweden. In the Baltic Sea, however, they are always
submerged as a result of lack of tides, ice-scouring during winter and
extended periods of low water levels in spring.
The vertical distribution in the Baltic usually ranged from 0 to 5-6 m
depth. For some nearshore locations, maximum depth down to 8 m has
been reported (Levring 1940; Hoffmann 1952; Waern 1952; Schwenke
1969; von Wachenfeldt 1975; Luther 1981; von Wachenfeldt et al. 1986);
in offshore clear waters it may reach down to depths of 12 m (Black 1978;
Kautsky et al. 1986).
While Fucus serratus penetrates as far as the Gothland Sea into the
Baltic, Fucus vesiculosus together with Chorda filum or Dictyosiphon
foeniculaceus extends community forming into the Gulf of Finland and
the Bothnian Bay till the salinity borderline of the mesohaline (3 PSU).
Below the Fucus belt, where substrate is suitable, red algal communities
W. Schramm
forms occurs in the Arcona Sea, the transition zone from the Western
Baltic to the Baltic proper, the latter being characterized by rather stable
salinities between 8 to 5 PSU, in contrast to the areas west of the Arcona
Sea with salinities changing between 10 to 20 PSU. Finally, a third critical
boundary can be observed in the Aland Sea, at the entrance to the
innermost parts of the Baltic, the Bothnian and Finnish gulfs, where
salinity decreases below 5 PSU down to 2-3 PSU.
Besides salinity, the substrate conditions in the Baltic determine to a
great extent type and distribution of the macrophytobenthos. Great parts
of the coasts of Denmark, Germany, Poland and eastern Baltic countries
consist of sandy or muddy soft bottoms which are only suitable for
growth of rooting plants. Hard substrates necessary for attachment of
seaweeds occur in the form of solid rock mainly along the Swedish and
Finnish coasts, or as glacial materials, particularly along sand cliffs,
which are common along the coasts of Denmark, Germany and partly
also of Poland.
The physiognomically important phytobenthic communities include
the mostly filamentous annual forms in the lower level of the "eulittoral",
followed further down by the Fucus belt and seagrass meadows, and the
red algal communities down to the distribution limits of the sublittoral.
Among these, the Fucus communities are most conspicuous. Fucus vesiculosus, the structurally most important seaweed in the Baltic, forms
together with about 30 species of associated macrofauna and macrophytes the most diverse benthic subsystem, important as spawning and
breeding grounds and shelter for many macrofauna and fish species
(Segerstraale 1944).
In fully marine areas, Fucus vesiculosus and Fucus serratus are usually
intertidal species, forming rather narrow belts as can still be observed on
the west coast of Sweden. In the Baltic Sea, however, they are always
submerged as a result of lack of tides, ice-scouring during winter and
extended periods of low water levels in spring.
The vertical distribution in the Baltic usually ranged from 0 to 5-6 m
depth. For some nearshore locations, maximum depth down to 8 m has
been reported (Levring 1940; Hoffmann 1952; Waern 1952; Schwenke
1969; von Wachenfeldt 1975; Luther 1981; von Wachenfeldt et al. 1986);
in offshore clear waters it may reach down to depths of 12 m (Black 1978;
Kautsky et al. 1986).
While Fucus serratus penetrates as far as the Gothland Sea into the
Baltic, Fucus vesiculosus together with Chorda filum or Dictyosiphon
foeniculaceus extends community forming into the Gulf of Finland and
the Bothnian Bay till the salinity borderline of the mesohaline (3 PSU).
Below the Fucus belt, where substrate is suitable, red algal communities