STATE OF THE ART AND TENDENCIES FOR CHANGES IN THE BLACK SEA BIODIVERSITY IN FRONT OF THE BULGARIAN COAST

摘要

Biodiversity of Black Sea flora and fauna is the most significant indicator for assessment the pelagic and benthic ecosystems ecological state. It is also of a great importance for the marine biological resources qualitative composition and quantitative distribution. In the report the present state of phytoplankton, macrophytobenthos, zooplankton, zoobenthos and ichlhyofauna in the Bulgarian Black sea sector in relation to their biodiversity and some tendencies for changing in recent period are discussed. In the phytoplankton communities a total of 254 species, varieties and forms from seven main taxonomic groups have been listed during the period 1953-1993.The dominant among them are the species from Bacillariophyta (108) and Dynophyta (100). During 1993-1996 period 45 additional species have been recorded. The long-term trends in the evolution of phytoplankton blooms in terms of species involved and taxonomic diversity are discussed. The composition of macrophytobenthos contains 157 species, which is 53% of the Black sea macroflora. A comparative analysis of the qualitative and saprobic structure of macrophytes during different periods is presented in the report. Zooplankton in front of the Bulgarian coast includes representatives of 10 main groups (Protozoa, Coelenterata, Ctcnophora, Nemathelminthes, Annelida, Arthropoda, Mollusca, Chordata, Chaetognata and Vertebrala).The problems connected with the progressive abundance increase of some species adaptive to eutrophication , strongly decreased quantity of more sensitive zooplankters and the nearly full extinction of other vulnerable species are commented. The data available on zoobenthos biodiversity show that the total number of identified species is 1370, belonging to 12 groups. In biocenological aspect 4 general types of benthic zoocenoses have been subdivided in 1954-1960.The first significant negative changes on benthic macrofauna were recorded 25 years ago. They were caused by the immigration of new species tolerant to the deteriorated environmental conditions - industrial pollution and increased eutrophication level. The recent state of macrozoobenthic cenoses in ecologically threatened areas is reported. Ichthyofauna inhabiting Bulgarian Black Sea area is represented by 46 Families andl27 species, but some of these are known as singular exemplars which doesn't ascertain their presence as regular. Out of all species 23 are ponticus relics, 10 - arctic-boreals and 94 - Mediterranean immigrants. The introduced restrictions for preserving fish from overcatch are presented. Despite all these measures resources of most commercial fish species and groups tend to decrease during 1981-1990 period due to the deteriorated environment conditions and overcatch. The stock of some species was sharply dropped down to the point of full extinction since 1969. Appropriate activities and measures for sustainable use of the marine biological resources and for coastal ecosystem biodiversity restoration are recommended.