446
F. Vasiliu
The formerly dominant diatom species have been replaced by dinoflagellates. Autotrophic species have partly been substituted by mixotrophic
organisms, for example, Exuviaella cordata or Goniaulax polygramma.
This change has probably supported the quantitative development of
zooplankton (Bodeanu and Roban 1989).
Dinoflagellates may have noxious effects on the benthic communities
by excretion of toxins, causing mass mortalities (Gomoiu 1985a). On this
"ecological background" the formerly characteristic fauna of the
Phyllophora community diminished significantly. Species of sponges,
crustaceans, amphipods and isopods, fish, etc. disappeared (Zaitev 1979).
The described effects occurred particularly in the area bounded by the
Chilia arm of the Danube and the Nistru bank. In August/September
1973, mass mortalities were observed at 6-23 m depth in an area
covering 350 000 ha. An exception were the polychaetes which are known
to be more resistant to toxins and to hypoxia. In the following years, the
phenomenon was observed again and it extended even to areas towards the open sea, covering 1 million ha in 1978. Also, large areas of
"Zemov's field" and of the bays of Karkinit, Tendra, and Egorlitk were
affected (Zaitev 1979).
19.4
Summary
The observed changes in the benthic vegetation of the Black Sea, in
particular along the Romanian coasts, are most probably the result of the
specific hydrographic conditions. Industry and intensive agriculture
along the coasts and in the drainage basin of the Black Sea, particularly in
the north with the Danube as the main conveyer of nutrients and pollutants, are the main sources of eutrophication with the following effects:
1. Disappearance of the Cystoseira belt, with the complete extinction of
C. crinita and a drastic decline in C. barbata, and a decline in biomass
from 10 500 t wet weight to only 89 t wet weight today.
2. Decreasing species numbers, especially among red and brown algae;
of the 10 1 species identified in 1968, only 69 can be found at present.
3. The last two species of marine phanerogams, Zostera marina and
Z. noltii have disappeared or are disappearing; only individual plants
or small patches can be found in Romanian waters.
4. The formerly qualitatively and quantitatively important Phyllophora
communities ("Zemov's field") show alarming signs of destruction.
The algal biomass has declined, and a great deal of the associated
F. Vasiliu
The formerly dominant diatom species have been replaced by dinoflagellates. Autotrophic species have partly been substituted by mixotrophic
organisms, for example, Exuviaella cordata or Goniaulax polygramma.
This change has probably supported the quantitative development of
zooplankton (Bodeanu and Roban 1989).
Dinoflagellates may have noxious effects on the benthic communities
by excretion of toxins, causing mass mortalities (Gomoiu 1985a). On this
"ecological background" the formerly characteristic fauna of the
Phyllophora community diminished significantly. Species of sponges,
crustaceans, amphipods and isopods, fish, etc. disappeared (Zaitev 1979).
The described effects occurred particularly in the area bounded by the
Chilia arm of the Danube and the Nistru bank. In August/September
1973, mass mortalities were observed at 6-23 m depth in an area
covering 350 000 ha. An exception were the polychaetes which are known
to be more resistant to toxins and to hypoxia. In the following years, the
phenomenon was observed again and it extended even to areas towards the open sea, covering 1 million ha in 1978. Also, large areas of
"Zemov's field" and of the bays of Karkinit, Tendra, and Egorlitk were
affected (Zaitev 1979).
19.4
Summary
The observed changes in the benthic vegetation of the Black Sea, in
particular along the Romanian coasts, are most probably the result of the
specific hydrographic conditions. Industry and intensive agriculture
along the coasts and in the drainage basin of the Black Sea, particularly in
the north with the Danube as the main conveyer of nutrients and pollutants, are the main sources of eutrophication with the following effects:
1. Disappearance of the Cystoseira belt, with the complete extinction of
C. crinita and a drastic decline in C. barbata, and a decline in biomass
from 10 500 t wet weight to only 89 t wet weight today.
2. Decreasing species numbers, especially among red and brown algae;
of the 10 1 species identified in 1968, only 69 can be found at present.
3. The last two species of marine phanerogams, Zostera marina and
Z. noltii have disappeared or are disappearing; only individual plants
or small patches can be found in Romanian waters.
4. The formerly qualitatively and quantitatively important Phyllophora
communities ("Zemov's field") show alarming signs of destruction.
The algal biomass has declined, and a great deal of the associated