When DNA puts ecological works back on the right track: genetic assessment and distribution patterns of mudsnail populations in the Evros Delta lagoons

Abstract

The present study aims to assess the distribution patterns of mudsnail populations in the Evros Delta lagoons and to investigate the key environmental variables affecting them. As a correct species assignment is crucial for ecological studies, the data presented here are substantiated using DNA sequences from the mitochondrial genome to verify the systematic status of the mudsnail taxon in question. A comparative molecular analysis involving almost all brackish-water taxa of Hydrobiinae indicates that the populations from the Evros Delta belong to the Pontic species Ventrosia maritima, a taxon that was not reported before from the Mediterranean. Moreover, it appears that in previous studies, the mudsnail populations from the Evros Delta were misidentified. Principal Component Analyses using environmental variables defined station groups among which V. maritima showed a significant variation in density. Mudsnail specimens were absent at stations with an immediate access to the sea (salinity 32-34 PSU, very fine to fine sand, organic matter 0.3-1.4 %), they showed intermediate densities (up to 3,000 ind./m 2 ) in innermost lagoonal parts (34-35 PSU, very fine sand, organic matter 1.0-1.4 %) and relatively high densities (up to 7,000 ind./m 2 ) only in isolated parts (15-17 PSU, fine sand, organic matter 0.5-0.8 %). Contact with the sea, which is strongly correlated with seawater renewal rate and hydrodynamism, was found to be the most important factor affecting mudsnail distributions. The data presented, being the first detailed ecological information available for V. maritima, are compared with the available information for other mudsnail taxa. The present study not only lays the foundation for future comparative eco-genetic works of mudsnail taxa, it also stresses the absolute need for the routine usage of molecular markers in ecological studies involving frequently utilized but systematically poorly understood invertebrate species.