Ewolucja jezior przybrzeżnych Niziny Gardzieńsko - Łebskiej na tle rozwoju środkowego wybrzeża Bałtyku w świetle badań malakologicznych

Wartykule przedstawiono syntezę dotychczasowego stanu wiedzy o rozwoju jezior przybrzeżnych Niziny Gardzieńsko- Łebskiej i środkowego wybrzeża Bałtyku, bazującą na wynikach badań malakologicznych. Analizy zespołów mięczaków z osadów limnicznych i morskich pozwoliły na wyróżnienie czterech faz rozwojowych jezior: wczesnoholoceńskiej fazy limniczno-bagiennej (trwającej od późnego glacjału do około 7500 lat 14C BP), fazy lagunowej (około 7500–6600 lat 14C BP), fazy przejściowej, słonawowodno-limnicznej (6600–4000 lat 14C BP) oraz fazy jeziornej (młodszej od 4000 lat 14C BP).W artykule wykazano, iż sukcesja malakofauny jest odzwierciedleniem regionalnych przemian środowiska, zarejestrowanych podobnymi zmianami zespołów fauny na całym wybrzeżu południowego Bałtyku.

The papers presents the synthesis of the current understanding of the evolution of coastal lakes in the Gardno-Łeba Lowland. Particular emphasis has been placed upon the influence of pre-Holocene surface topography on lake basin evolution and water level changes caused by the transgression of southern Baltic. Malacological analysis reveals four phases in lake environmental history: limnic-swampy phase, lagoon phase, transitional brackish-limnic phase, and limnic phase. The oldest, early Holocene limnic-swampy phase in the Gardno-Łeba Lowland area is represented by Preboreal and Boreal assemblages with freshwater fauna, described as Planorbis phase. It is characterized by rich assemblages, in terms of both number of individuals and species, composed of members of Planorbis, accompanied by Bithynia tentaculata, Valvata piscinalis and Pisidium. The lagoon-marine phase, described as Scrobicularia phase (7500–6000 BP), is defined by a homogeneous assemblage of malacofauna, consisting entirely of brackish and marine species, such as Hydrobia ulvae, H. ventrosa, Cerastoderma glaucum, Macoma baltica, Mytilus edulis and indicative Lusitanian and Lower Boreal species for the Mesoholocene of the southern Baltic, including Scrobicularia plana, Rissoa membranaea, R. inconspicua, Parvicardium exiguum and Mysella bidentata. The transitional brackish-limnic phase Cardium (6600–4000 BP) is correlated with late Littorina transgressive phases. It is dominated by Cardium glaucum, with minor percentage of Hydrobia ventrosa, Mytilus edulis, and sporadic freshwater species. The limnic Lymnaea phase corresponds with the post-Littorina period (4000 BP–1900 AD). The onset of this phase is marked by an assemblage with dominating Theodoxus fluviatilis, the optimum – by Lymnea peregra assemblages, whereas frequent Bithynia tentaculata indicate the end of the phase. The youngest Potamopyrgus phase includes recent lake sediments from the last 100 years and is marked by the first appearance of a new mollusc species in the coastal zone of the Baltic – Potamopyrgus antipodarium. The malacofauna succession identified in the coastal lakes in the Gardno-Łeba Lowland reflects regional environmental change, recorded by similar faunal assemblages throughout the southern coast of the Baltic.