The Baltic Sea and Its Transition Zones
153
simple water viewer, the visibility in 1987/1988 was usually reduced to
2-3 m depth.
Another indication of changes in light climate may be that since
summer 1989 in the upper littoral of Kiel Fjord Laminaria saccharina
can increasingly be observed, a seaweed which earlier was considered as
a typical low-light adapted deep-water form in the Kiel Bay. Recent
long-term registration of light conditions in Kiel Fjord, in connection
with transplantation experiments and laboratory studies on light requirement of Fucus vesiculosus, revealed that annual light conditions at 2 m
depth are not sufficient for a positive energy budget of the bladder-wrack
(B. Schaffelke, pers. comm. 1994).
Apart from competition between plants, the impact of animals associated with Fucus may play a role. Settlement and mass development of
young Mytilus edulis on Fucus plants, particularly when overgrown with
epiphytes may have detrimental effects, as also observed for Halydrys
siliquosa (Lundlilv et al. 1986). The increased epiphytic filamentous algae
favour mass development of Idotea baltica, the adults of which also graze
on Fucus and may daily consume half of their body weight (Jansson
1974; Salemaa 1987). Griitzmacher (1983) showed in in situ culture experiments that Idotea reduced the biomass of Fucus test plants by 30%
within 2 months.
Parallel to the decline of Fucus and its decreasing depth distribution,
significant changes were also observed for the sublittoral communities in
Kiel Bight. A large-scale quantitative investigation employing SCUBA
diving and underwater television during 1985 -1986 (Breuer and
Schramm 1988) was compared to a semi- quantitative survey carried out
during 1962-1964 (Schwenke 1964, 1969). During this period, distinct
changes in biomass, species composition and depth distribution occurred. The maximum depth distribution of the vegetation changed from
20 to 18 m. Biomass increased above the 12 m level with exception of the
6 m level (Fig. 5.12). Extended Furcellaria lumbricalis populations disappeared and have been replaced by Coccotylus (formerly Phyllophora)
truncata and Phycodrys rubens which became the predominant species.
These species together with filamentous red and brown algae penetrated
to depths between 2-6 m, formerly inhabited by Focus and seagrass
communities (W. Schramm, unpubl. data).
From the transition zone of the Baltic, i.e. the Belt Sea and the Sound,
reports on changes in the benthic vegetation stem mainly from Swedish
and Danish monitoring programmes, which were started in the mid1970s and early 1980s. Along the coasts of southern Sweden (Skane) and
the Sound a strong decline of Fucus vesiculosus was observed from 1983
to 1985, probably as a result of ice-scouring during the hard winter
153
simple water viewer, the visibility in 1987/1988 was usually reduced to
2-3 m depth.
Another indication of changes in light climate may be that since
summer 1989 in the upper littoral of Kiel Fjord Laminaria saccharina
can increasingly be observed, a seaweed which earlier was considered as
a typical low-light adapted deep-water form in the Kiel Bay. Recent
long-term registration of light conditions in Kiel Fjord, in connection
with transplantation experiments and laboratory studies on light requirement of Fucus vesiculosus, revealed that annual light conditions at 2 m
depth are not sufficient for a positive energy budget of the bladder-wrack
(B. Schaffelke, pers. comm. 1994).
Apart from competition between plants, the impact of animals associated with Fucus may play a role. Settlement and mass development of
young Mytilus edulis on Fucus plants, particularly when overgrown with
epiphytes may have detrimental effects, as also observed for Halydrys
siliquosa (Lundlilv et al. 1986). The increased epiphytic filamentous algae
favour mass development of Idotea baltica, the adults of which also graze
on Fucus and may daily consume half of their body weight (Jansson
1974; Salemaa 1987). Griitzmacher (1983) showed in in situ culture experiments that Idotea reduced the biomass of Fucus test plants by 30%
within 2 months.
Parallel to the decline of Fucus and its decreasing depth distribution,
significant changes were also observed for the sublittoral communities in
Kiel Bight. A large-scale quantitative investigation employing SCUBA
diving and underwater television during 1985 -1986 (Breuer and
Schramm 1988) was compared to a semi- quantitative survey carried out
during 1962-1964 (Schwenke 1964, 1969). During this period, distinct
changes in biomass, species composition and depth distribution occurred. The maximum depth distribution of the vegetation changed from
20 to 18 m. Biomass increased above the 12 m level with exception of the
6 m level (Fig. 5.12). Extended Furcellaria lumbricalis populations disappeared and have been replaced by Coccotylus (formerly Phyllophora)
truncata and Phycodrys rubens which became the predominant species.
These species together with filamentous red and brown algae penetrated
to depths between 2-6 m, formerly inhabited by Focus and seagrass
communities (W. Schramm, unpubl. data).
From the transition zone of the Baltic, i.e. the Belt Sea and the Sound,
reports on changes in the benthic vegetation stem mainly from Swedish
and Danish monitoring programmes, which were started in the mid1970s and early 1980s. Along the coasts of southern Sweden (Skane) and
the Sound a strong decline of Fucus vesiculosus was observed from 1983
to 1985, probably as a result of ice-scouring during the hard winter