The Northern Adriatic Sea
387
16.6 Algal Biomass
The northern Adriatic benthic algal vegetation exhibited relatively high
biomass values, in particular in the upper sublittoral (Span 1969; Munda
1972, 1973, 1979).
A further effect of eutrophication is obvious in changes in the algal
biomass. A degradation or absence of associations of perennial algae led
to a decrease in biomass in most habitats. In heavily polluted sites, a
transitent increase in the fresh weight biomass was observed for annual
species, which prosper in nutrient-rich habitats (e.g. Ulva rigida,
Enteromorpha intestinalis, E. prolifera, E. clathrata, Blidingia minima,
several Cladophora species, Ectocarpus siliculosus, Pilayella littoralis and
Scytosiphon lomentaria; Fig. 16.8).
Some data on annual variations in biomass in relation to exposure for
the area around Rovinj are presented in Fig. 16.8. In the late sixties, the
eulittoral zone was dominated by Fucus virsoides. Year to year variations
exhibited a gradual decrease in biomass of the Fucus settlements along
the mainland coasts, whereas on the islands an increase was observed. In
highly exposed habitats, the Fucus settlements were replaced by
Ceramium diaphanum during the years before the severe pollution
impact. In the late 1970s when observations in the same area were
repeated the Fucus settlements were replaced by stands of Blidingia
minima, Cladophora species and Enteromorpha intestinalis. The average
fresh weight biomass of the eulittoral algal settlements decreased on the
islands and in highly exposed mainland habitats. At other mainland sites
the fresh weight biomass of the spring annuals exceeded that of the
previous Fucus stands or was at the same level. The average yearly
biomass values are based on vernal observations, since during summer
the eulittoral slopes were bare.
At the eulittora1!sublittoral junction Ceramium species along with the
other red algae declined gradually during the first years of the field
studies. After the severe pollution impact they were replaced by the
association of codominant Scytosiphon lomentaria-Ulva rigida with accompanying Enteromorpha species. Thus the fresh weight biomass was
approximately fourfold that of the previous red algae stands during
spring (Fig. 16.8).
In the upper sublittoral, Cystoseira settlements were dominant, with
irregular year to year variations in both exposed and sheltered habitats.
Cystoseira adriatica and C. crinita were dominant in the former, C. compressa and C. barbata in the latter habitats. These Cystoseira stands
deteriorated after the severe pollution impact in the Rovinj area and were
387
16.6 Algal Biomass
The northern Adriatic benthic algal vegetation exhibited relatively high
biomass values, in particular in the upper sublittoral (Span 1969; Munda
1972, 1973, 1979).
A further effect of eutrophication is obvious in changes in the algal
biomass. A degradation or absence of associations of perennial algae led
to a decrease in biomass in most habitats. In heavily polluted sites, a
transitent increase in the fresh weight biomass was observed for annual
species, which prosper in nutrient-rich habitats (e.g. Ulva rigida,
Enteromorpha intestinalis, E. prolifera, E. clathrata, Blidingia minima,
several Cladophora species, Ectocarpus siliculosus, Pilayella littoralis and
Scytosiphon lomentaria; Fig. 16.8).
Some data on annual variations in biomass in relation to exposure for
the area around Rovinj are presented in Fig. 16.8. In the late sixties, the
eulittoral zone was dominated by Fucus virsoides. Year to year variations
exhibited a gradual decrease in biomass of the Fucus settlements along
the mainland coasts, whereas on the islands an increase was observed. In
highly exposed habitats, the Fucus settlements were replaced by
Ceramium diaphanum during the years before the severe pollution
impact. In the late 1970s when observations in the same area were
repeated the Fucus settlements were replaced by stands of Blidingia
minima, Cladophora species and Enteromorpha intestinalis. The average
fresh weight biomass of the eulittoral algal settlements decreased on the
islands and in highly exposed mainland habitats. At other mainland sites
the fresh weight biomass of the spring annuals exceeded that of the
previous Fucus stands or was at the same level. The average yearly
biomass values are based on vernal observations, since during summer
the eulittoral slopes were bare.
At the eulittora1!sublittoral junction Ceramium species along with the
other red algae declined gradually during the first years of the field
studies. After the severe pollution impact they were replaced by the
association of codominant Scytosiphon lomentaria-Ulva rigida with accompanying Enteromorpha species. Thus the fresh weight biomass was
approximately fourfold that of the previous red algae stands during
spring (Fig. 16.8).
In the upper sublittoral, Cystoseira settlements were dominant, with
irregular year to year variations in both exposed and sheltered habitats.
Cystoseira adriatica and C. crinita were dominant in the former, C. compressa and C. barbata in the latter habitats. These Cystoseira stands
deteriorated after the severe pollution impact in the Rovinj area and were