396
I.M. Munda
still relatively abundant or even belt-forming in the upper sublittoraL
Furthermore, an upwards migration of deep-water species, such as Halimeda tuna, Pterocladia capillacea, Gigartina acicularis, Gracilaria verrucosa, Codium effusum, Codium vermilara, was recently observed. The
upwards migration of these sciaphilic species might be related to the
increased turbidity of the northern Adriatic water.
In heavily polluted sites, a series of disturbances is even more pronounced. Among such disturbances are excess of nutrients, input of
suspended and colloidally dispersed materials, bacteria, humic substances, detergents and heavy metals, along with increased turbidity. A consequence of eutrophication is also a decreased oxygen concentration,
leading locally to anoxic conditions. The interacting effects of such extremely adverse conditions have excluded fucoids and most red algae
from the vegetation and totally changed the zonation patterns and the
dominant algal associations (cf. Figs. 16.3 to 16.6).
Only species with a wide ecological valence are able to exist and
prosper in eutrophicated habitats. Weare therefore concerned mainly
with seasonal floristic elements with simple thalli and a short life span,
mostly vernal species. These algae are often found in estuaries and other
brackish habitats, since they are able to tolerate wide ranges and rapid
fluctuations of temperature, salinity, dissolved nutrients and other
substances drained in by the rivers (e.g. green algae of the genera Blidingia, Enteromorpha and Cladophora; Ulva rigida, Scytosiphon lomentaria,
Ectocarpus siliculosus, Pilayella littoralis). Only a few red algae can
tolerate such extreme conditions. It is noteworthy that Ceramium
cilia tum, in contrast to other species of this genus, was found partly
buried in sand in highly polluted habitats.
A comparison of the benthic algal vegetation of differently polluted
sites from the northern Adriatic (Munda 1993a,b) revealed different
zonation patterns (Figs. 16.3 to 16.6) along with a decreased depth penetration of macro algae. This phenomenon, caused by increased turbidity in
eutrophicated habitats as well as grazing by sea urchins, was also observed in other areas (Kautsky et al. 1986; Breuer and Schramm 1988;
Rueness and Fredriksen 1991; Vogt and Schramm 1991).
Pronounced year to year variations within algal associations were
followed in the investigated areas of the northern Adriatic. Transient
restitution of Cystoseira and Fucus virsoides stands with subsequent
degradations were observed, as well as the disappearance of some species
with simultaneous reappearance of others (e.g. Nemastoma dichotoma,
Petalonia fascia, Cladostephus spongiosus f. verticillatus, Acrosorium
venulosum, Dasya spp.). In the eulittoral, during spring and summer
months, a dense girdle of Codium fragile var. tomentosoides appeared in
I.M. Munda
still relatively abundant or even belt-forming in the upper sublittoraL
Furthermore, an upwards migration of deep-water species, such as Halimeda tuna, Pterocladia capillacea, Gigartina acicularis, Gracilaria verrucosa, Codium effusum, Codium vermilara, was recently observed. The
upwards migration of these sciaphilic species might be related to the
increased turbidity of the northern Adriatic water.
In heavily polluted sites, a series of disturbances is even more pronounced. Among such disturbances are excess of nutrients, input of
suspended and colloidally dispersed materials, bacteria, humic substances, detergents and heavy metals, along with increased turbidity. A consequence of eutrophication is also a decreased oxygen concentration,
leading locally to anoxic conditions. The interacting effects of such extremely adverse conditions have excluded fucoids and most red algae
from the vegetation and totally changed the zonation patterns and the
dominant algal associations (cf. Figs. 16.3 to 16.6).
Only species with a wide ecological valence are able to exist and
prosper in eutrophicated habitats. Weare therefore concerned mainly
with seasonal floristic elements with simple thalli and a short life span,
mostly vernal species. These algae are often found in estuaries and other
brackish habitats, since they are able to tolerate wide ranges and rapid
fluctuations of temperature, salinity, dissolved nutrients and other
substances drained in by the rivers (e.g. green algae of the genera Blidingia, Enteromorpha and Cladophora; Ulva rigida, Scytosiphon lomentaria,
Ectocarpus siliculosus, Pilayella littoralis). Only a few red algae can
tolerate such extreme conditions. It is noteworthy that Ceramium
cilia tum, in contrast to other species of this genus, was found partly
buried in sand in highly polluted habitats.
A comparison of the benthic algal vegetation of differently polluted
sites from the northern Adriatic (Munda 1993a,b) revealed different
zonation patterns (Figs. 16.3 to 16.6) along with a decreased depth penetration of macro algae. This phenomenon, caused by increased turbidity in
eutrophicated habitats as well as grazing by sea urchins, was also observed in other areas (Kautsky et al. 1986; Breuer and Schramm 1988;
Rueness and Fredriksen 1991; Vogt and Schramm 1991).
Pronounced year to year variations within algal associations were
followed in the investigated areas of the northern Adriatic. Transient
restitution of Cystoseira and Fucus virsoides stands with subsequent
degradations were observed, as well as the disappearance of some species
with simultaneous reappearance of others (e.g. Nemastoma dichotoma,
Petalonia fascia, Cladostephus spongiosus f. verticillatus, Acrosorium
venulosum, Dasya spp.). In the eulittoral, during spring and summer
months, a dense girdle of Codium fragile var. tomentosoides appeared in