07C1
Hypersaline coastal lakes and swamps
Relationships with habitat classifications. EUNIS: C1.5113 Ponto-Pannonic salt lake; PAL. CLASS.: 23.113 Ponto-Pannonic salt lakes; HD 92/43: 1150 *Coastal lagoons.
Conservation status. BDA, BC, HD.
Category. Endangered [EN – A1, 2 B1 C2 D3 E2 F2 G2 H2 I J L2].
General characteristics. These lakes are usually small or medium in size (less than 1 ha), hyper- of mixohaline, holo- or polymictic water bodies with clay-muddy or sandy bottom and banks. Atanasovsko and Pomoriisko lakes are the only large mixo-hyperhaline water bodies that cover relatively large areas. The altitude of these lakes is 0–5 m. They derive mostly from lagoons. Their depth is small, from 0,5 to 2,5 m. They are separated from the sea with sandy strips that periodically are overflooded by the sea waves, mainly in autumn and winter, hence the salinity is lower. The rains in spring also decrease the salinity. In summer and autumn the salinity increases since evaporation is more intense compared to the water influx. Typical habitats are Shablenska Tuzla, Nanevska Tuzla and Balchishka Tuzla localities, Pomoriisko and Atanasovsko lakes and Alepu swamp. The varying salinity that differs from the one of the seawater (between 3–4 and over 100 ‰) and the large fluctuations of the dissolved oxygen and the oxygen saturation (from 20 to 120%) are typical for such habitats. The banks and the larger part of the water surfaces are occupied by semi-submerged hydrophytic vegetation. Their succession stage is eutrophic, polimictic, sometime very shallow water bodies that are 0,5–2,5 m deep. In some cases they are drying water bodies poor in zoobenthic communities. The zooplankton is poor in species but with high quantity maximums, with a prevalence of crustacean benthos-plankton species.
Characteristic taxa.
- Plants: Algae – Cryptophyta: Cryptomonas spp., Chroomonas acuta; Bacillariophyta: Navicula spp., Dunalliella papura (often dominates in autumn); Vascular plants – Bolboschoenus maritimus, Phragmites australis, Ruppia maritima, Typha latifolia, Zostera marina.
- Animals: Polychaets – Nephtys spp; Crustaceans – Arctodiaptomus salinus, Euritemora velox, Paracartia latisetoza, Palemon elegans, Crangon spp., Idotea baltica, Paramisis spp. Insect larvae are typical when the salinity is high (60–90 ‰) – Chironomus valkanovi, Halocladius mediterraneus. They can reach 90% of the total number of benthic organisms: Birds – Himantopus himantopus, Recurvirosta avosetta, Sterna sandvicensis.
Distribution in Bulgaria. Black Sea coast, mainly northeastern and southeastern parts; northwards from Varna town (Shablenska Tuzla, Nanevska Tuzla and Balchishka Tuzla localities) and near Burgas town (Atanasovkso and Pomoriisko lakes, Alepu swamp).
Conservation importance. The habitat is important for the preservation of a number of invertebrates that originate from Asia Minor and occur in single localities in Bulgaria. It is also important for the preservation of tens of bird species of high conservation value. The hypersaline lakes serve as a trophic basis, and wintering or rest place for rare and endangered migratory birds (Via Pontica). The only nesting colony of the Sanwich tern is in these lakes and this is the most northeastern colony of the species. The bat community in Atanasovsko and Pomoriisko lakes has relatively permanent composition in summer and autumn. Thousands of local and migratory bats find their food there: Myotis daubentonii, Nyctalus noctula, Pipistrellus pipistrellus, P. nathusii, Eptesicus serotinus.
Threats. Climate aridisation, agriculture (ploughing, fertilization, and other activities in the neighbouring arable land), influx of biogenic elements that stimulate the development of the phytoplankton that causes the “blooming” of the lakes. Urbanization – building and exploitation of tourist complexes, sanatoriums, as is the case in Balchishka Tuzla locality, influx of non-purified waste water from the tourist complexes, hence a decrease of the salinity of the water bodies.
Conservation measures taken. The habitat is in Annex № 1 of BDA and is of conservation priority. Parts of the habitat are within protected areas – Atanaskovsko Ezero (lake) Managed Nature Reserve, Taukliman Protected Site – Nanevska Tuzla locality, Pomoriisko Ezero (lake) Protected Site and sites from the European Ecological Network NATURA 2000. Some of the water bodies (e.g. Balchishka Tuzla locality and Pomoriisko lake) are protected also as a source of healing mud for balneology and rehabilitation.
Conservation measures needed. Effective control on the construction activities, designation of buffer zones in order to limit the influx of biogenic elements from the agricultural land; control on the quantities and exploitation level of anaerobic sediments for medical purposes (as in Balchishka Tuzla locality); restoration of the broken connections with the sea where necessary; influx of seawater to Balchishka Tuzla localities over the existing dyke in order to create a connection between the northeastern and southwestern parts of the lake that are separated by the dyke.
References. Ivanov et al. 1964; Golemanski & Naidenov 1998.
Authors: Dimitar Kozhuharov, Jordan Uzunov, Vasil Vasilev
