Invertebrate Animals (Metazoa: Invertebrata) of the Atanasovsko Lake, Bulgaria

Abstract

The role of the Atanasovsko Lake for storage and protection of the specific faunistic diversity, characteristic of the hyper-saline lakes of the Bulgarian seaside is presented. The fauna of the lake and surrounding waters is reviewed, the taxonomic diversity and some zoogeographical and ecological features of the invertebrates are analyzed. The lake system includes from freshwater to hyper-saline basins with fast changing environment. A total of 6 types, 10 classes, 35 orders, 82 families and 157 species are known from the Atanasovsko Lake and the surrounding basins. They include 56 species (35.7%) marine and marine-brackish forms and 101 species (64.3%) brackish-freshwater, freshwater and terrestrial forms, connected with water. For the first time, 23 species in this study are established (12 marine, 1 brackish and 10 freshwater). The marine and marine-brackish species have 4 types of ranges - Cosmopolitan, Atlantic-Indian, Atlantic-Pacific and Atlantic. The Atlantic (66.1%) and Cosmopolitan (23.2%) ranges that include 80% of the species, predominate. Most of the fauna (over 60%) has an Atlantic-Mediterranean origin and represents an impoverished Atlantic-Mediterranean fauna. The freshwater-brackish, freshwater and terrestrial forms, connected with water, that have been established from the Atanasovsko Lake, have 2 main types of ranges - species, distributed in the Palaearctic and beyond it and species, distributed only in the Palaearctic. The representatives of the first type (52.4%) predominate. They are related to the typical marine coastal habitats, optimal for the development of certain species. The second type combines Palaearctic (20.0%), Eurosiberian (9.5%) and Mediterranean (15.2%) taxa. Caspian relicts lack in the Atanasovsko Lake. That is probably related to the specific hydrological regime, technological processes of the salt producing and the highly variable hyper-saline nature of the lake. Of the Pontic species Chironomus valkanovi is established. Of the benthic forms Cerastoderma glaucum (to 134376 ind/m2), Ecrobia ventrosa (to 19800 ind/m2), Abra segmentum and Cyprideis torosa (to 77440 ind/m2) dominate. Corophium volutator is a mass species in all seasons and is one of the most adapted inhabitants of the saltpans. The Cosmopolitan Acartia clausi reaches high numbers (to 130000 ind/m3) as well. Typical for the Atanasovsko Lake are the halobionts Artemia parthenogenetica and Artemia salina that reach densities up to 3400 ind/l water. The presence of 6 types of foreign immigrants (Ficopomatus enigmaticus, Amphibalanus eburneus, Rapana venosa, Physella acuta, Anadara kagoshimensis and Mya arenaria) is established. Of the invertebrate animals of the Atanasovsko Lake 3 species are included in the Black Sea Red Data Book and 8 species - in the European and IUCN Red Lists.

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