PHYTOPLANKTON COMPOSITION OF VAYA LAKE (2004–2006)

Abstract

Vaya (= Burgas Lake), is the biggest natural lake in Bulgaria and the shallowest Black Sea Costal lake. With regard of its origin, Vaya is a liman and recently it is mixooligohaline with fluctuating halinity due to a siltated channel connection with the Black Sea. The lake is located on the ‘Via Pontica’ ornithological migratory route and is important for the conservation of rare and endangered species of national, European and global significance. The lake is a Ramsar site, a Protected area and Natura 2000 site, included as critically endangered in the Red List of Bulgarian Wetlands. During the last decades Vaya has undergone significant changes due to different anthropogenic factors, which disturb the water balance of the lake and lead to introduction of biogenic elements in the wetland with a negative effect on the chemical composition of the water with impacts on the flora and fauna of the aquatic ecosystem. The phytoplankton studies, represented in this work, have been conducted during the summer and autumn months of three consecutive years – 2004–2006. A rich species composition has been established – 165 species, 8 varieties and 1 form of 80 genera from 8 divisions. The green algae (Chlorophyta and Streptophyta) are characterized by the biggest number of taxa (89), followed by the blue-green algae (Cyanoprokaryota – 51), among which the tropical toxic invasive species Cylindrospermopsis raciborskii, was detected for the fi rst time in Vaya lake. Most of the species have low frequency quotients and only three can be pointed as widely distributed during the studied period (Planktothrix agardhii, Pseudanabaena limnetica, Scenedesmus acuminatus). On the basis of data from the same periods of close preceding years, a comparison is made between the algal flora of Vaya and other Black Sea coastal wetlands – Shabla, Ezerets and Dourankoulak. In all of them, 30 common taxa have been registered. A comparison has been done also between the obtained data on the recent taxonomic composition and former data on lake algal flora of other authors. The results show the general negative trend in the development of Vaya wetland with increase eutrophication.