386
I.M. Munda
purpuriferum, Dudresnaya verticillata and several representatives of the
genera Ceramium, Polysiphonia, Dasya, Antithamnion, Callithamnion,
Aglaothamnion, Bryopsis and some others. Some of the species declined
in quantity and were only found in single specimens in undisturbed or
relatively undisturbed localities, distant from the outfalls.
The number of species was lowest in the eulittoral zone, which was
devoid of Fucus virsoides (Fig. 16.7 A). Seasonal maxima were found in
April and October. The number of species was notably higher at 1 and
3 m depths and decreased again in the lower sublittoral, at 7 m depth. In
the eulittoral and at 1 m depth, seasonal maxima were found during the
same seasons, i.e. in April and October, due to the appearance of spring
annuals and several green algae in autumn. At 3 and 7 m depths, the
seasonal maxima in species number occurred in June.
The decrease in the species number in the lower sublittoral, at 7 m, is
due to the disappearance of deep-water fucoids along with their epiphytic cover. Crustose floristic elements predominate at this level and thus
seasonal variations were less pronounced than at 3 m depth.
At the intermediate depth of 1 and 3 m the number of recorded
species also varied due to changes in the epiphytic cover of the still
present Cystoseira species and Halopythis incurvus.
Looking at the heavily polluted sites, the number of species notably
decreased due to the eradication of all the fucoids and red algae from the
residual vegetation. Scytosiphon lomentaria and Ectocarpus siliculosus
were the only representatives of the Phaeophyta there, with occasional
findings of Pilayella littoral is. Among the Chlorophyta, representatives of
the genera Uiva, Enteromorpha, Blidingia, Chaetomorpha and Cladophora
were common and Cyanobacteria proved also to be successful in some
eutrophicated habitats (Oscillatoria, Lyngbya and Spirulina species).
A significant decline in the number of species towards the sources of
pollution was demonstrated also for the harbours of Makarska and Split in
the middle Adriatic (Span and Antolic 1991). In the harbours, a twofold
decrease in species number was recorded compared to areas just outside,
and again a 2.5- to 3-fold decrease close to the sewage outlets. The
decrease in species number was most pronounced for the red algae and
less for the brown and green algae. The latter remained numerically
constant within the harbour and close to the sources of pollution. In
control areas Rhodophyta were numerically dominant, while they were in
a minority within the harbour areas, where finally Chlorophyta dominated.
Long-term observations in other areas (Rueness and Fredriksen 1991)
have revealed a prominent decrease in species number in the Oslofjord
during the last four decades. These changes were particularly conspicuous below 10m depth.
I.M. Munda
purpuriferum, Dudresnaya verticillata and several representatives of the
genera Ceramium, Polysiphonia, Dasya, Antithamnion, Callithamnion,
Aglaothamnion, Bryopsis and some others. Some of the species declined
in quantity and were only found in single specimens in undisturbed or
relatively undisturbed localities, distant from the outfalls.
The number of species was lowest in the eulittoral zone, which was
devoid of Fucus virsoides (Fig. 16.7 A). Seasonal maxima were found in
April and October. The number of species was notably higher at 1 and
3 m depths and decreased again in the lower sublittoral, at 7 m depth. In
the eulittoral and at 1 m depth, seasonal maxima were found during the
same seasons, i.e. in April and October, due to the appearance of spring
annuals and several green algae in autumn. At 3 and 7 m depths, the
seasonal maxima in species number occurred in June.
The decrease in the species number in the lower sublittoral, at 7 m, is
due to the disappearance of deep-water fucoids along with their epiphytic cover. Crustose floristic elements predominate at this level and thus
seasonal variations were less pronounced than at 3 m depth.
At the intermediate depth of 1 and 3 m the number of recorded
species also varied due to changes in the epiphytic cover of the still
present Cystoseira species and Halopythis incurvus.
Looking at the heavily polluted sites, the number of species notably
decreased due to the eradication of all the fucoids and red algae from the
residual vegetation. Scytosiphon lomentaria and Ectocarpus siliculosus
were the only representatives of the Phaeophyta there, with occasional
findings of Pilayella littoral is. Among the Chlorophyta, representatives of
the genera Uiva, Enteromorpha, Blidingia, Chaetomorpha and Cladophora
were common and Cyanobacteria proved also to be successful in some
eutrophicated habitats (Oscillatoria, Lyngbya and Spirulina species).
A significant decline in the number of species towards the sources of
pollution was demonstrated also for the harbours of Makarska and Split in
the middle Adriatic (Span and Antolic 1991). In the harbours, a twofold
decrease in species number was recorded compared to areas just outside,
and again a 2.5- to 3-fold decrease close to the sewage outlets. The
decrease in species number was most pronounced for the red algae and
less for the brown and green algae. The latter remained numerically
constant within the harbour and close to the sources of pollution. In
control areas Rhodophyta were numerically dominant, while they were in
a minority within the harbour areas, where finally Chlorophyta dominated.
Long-term observations in other areas (Rueness and Fredriksen 1991)
have revealed a prominent decrease in species number in the Oslofjord
during the last four decades. These changes were particularly conspicuous below 10m depth.