The Northern Adriatic Sea
393
green algae from polluted habitats (Munda 1988, 1990). The mannitol
content in brown algae was usually reduced compared to the controls,
indicating a decreased assimilatory activity. In Fucus virsoides plants
protruding into low-salinity areas, similar changes in the chemical composition were noted, along with a pronounced reduction in the thallus
size, related to the salinity gradient. A similar reduction in size was
found also in plants from moderately polluted habitats.
Autecological tests carried out with fucoids in vitro (Munda 1982b)
showed that excess nutrient salts as well as untreated harbour water
severely depresses growth performance in Fucus virsoides and can be
lethal for Cystoseira species, the latter deteriorating in nutrient-enriched
media after 1 to 2 weeks. Fucus virsoides, on the other hand, was able to
survive, growing slightly, when nitrate was supplied separately. In the
experiments, growth was reduced at the higher temperature, i.e. at 100e.
The separate addition of phosphate revealed another pattern: a considerable temperature-enhanced growth performance at its lower concentration and severe growth depressions at the higher concentration at SoC, or
lethal effects at lOoC. A combination of both salts severely decreased
growth rates and induced fruiting at SoC, but was lethal at 100e.
In general, susceptibility towards organic pollutants (untreated harbour water) or excess nutrients increases with temperature. The higher
experimental temperature of lOoC, however, corresponds to the winter
temperature in the northern Adriatic. We may expect that even higher
temperatures would induce a lethal effect of the pollutants mentioned,
without previous growth.
From this, we assume that an excess of nutrients in combination with
organic substances excludes fucoids from sewage-influenced areas
because of negative effects on their growth performance and metabolic
activities.
Previous experiments with Atlantic fucoids also showed that untreated
harbour water severely depressed the assimilation rate and at the same
time enhanced respiration (Munda 1974b).
A further cause for reduced settlement of benthic marine algae is the
occurrence of occasional extensive mucus aggregations, which occurred
in the northern Adriatic waters during summer months of the last few
years. These mucus aggregations. deriving from plankton blooms, are
mixed with terrigenous humic substances and contain assemblages of
phytoplankton, bacteria and protozoa, embedded into an amorphous
matrix. They contribute significantly to the metabolism of the pelagic
system (Herndl 1988; Herndl and Peduzzi 1988; Herndl et al. 1989). The
aggregations pass through different stages, from floccula over "stringers"
to large coagulations, which can cover macro algae and benthic animals
393
green algae from polluted habitats (Munda 1988, 1990). The mannitol
content in brown algae was usually reduced compared to the controls,
indicating a decreased assimilatory activity. In Fucus virsoides plants
protruding into low-salinity areas, similar changes in the chemical composition were noted, along with a pronounced reduction in the thallus
size, related to the salinity gradient. A similar reduction in size was
found also in plants from moderately polluted habitats.
Autecological tests carried out with fucoids in vitro (Munda 1982b)
showed that excess nutrient salts as well as untreated harbour water
severely depresses growth performance in Fucus virsoides and can be
lethal for Cystoseira species, the latter deteriorating in nutrient-enriched
media after 1 to 2 weeks. Fucus virsoides, on the other hand, was able to
survive, growing slightly, when nitrate was supplied separately. In the
experiments, growth was reduced at the higher temperature, i.e. at 100e.
The separate addition of phosphate revealed another pattern: a considerable temperature-enhanced growth performance at its lower concentration and severe growth depressions at the higher concentration at SoC, or
lethal effects at lOoC. A combination of both salts severely decreased
growth rates and induced fruiting at SoC, but was lethal at 100e.
In general, susceptibility towards organic pollutants (untreated harbour water) or excess nutrients increases with temperature. The higher
experimental temperature of lOoC, however, corresponds to the winter
temperature in the northern Adriatic. We may expect that even higher
temperatures would induce a lethal effect of the pollutants mentioned,
without previous growth.
From this, we assume that an excess of nutrients in combination with
organic substances excludes fucoids from sewage-influenced areas
because of negative effects on their growth performance and metabolic
activities.
Previous experiments with Atlantic fucoids also showed that untreated
harbour water severely depressed the assimilation rate and at the same
time enhanced respiration (Munda 1974b).
A further cause for reduced settlement of benthic marine algae is the
occurrence of occasional extensive mucus aggregations, which occurred
in the northern Adriatic waters during summer months of the last few
years. These mucus aggregations. deriving from plankton blooms, are
mixed with terrigenous humic substances and contain assemblages of
phytoplankton, bacteria and protozoa, embedded into an amorphous
matrix. They contribute significantly to the metabolism of the pelagic
system (Herndl 1988; Herndl and Peduzzi 1988; Herndl et al. 1989). The
aggregations pass through different stages, from floccula over "stringers"
to large coagulations, which can cover macro algae and benthic animals