Transitional Waters Bulletin TWB, Transit. Waters Bull. 3(2007), 23-25 ISSN 1825-229X, DOI 10.1285/i1825229Xv1n3p23 http://siba2.unile.it/ese/twb © 2007 University of Salento - SIBA http://siba2.unile.it/ese RESEARCH ARTICLE The biological system of the lower salinity ponds in Kalloni Saltworks (NE. Aegean Sea, Greece): phytoplankton and macrobenthic invertebrates A. Evagelopoulos*, E. Spyrakos & D. Koutsoubas Department of Marine Sciences, Faculty of the Environment, University of the Aegean, University Hill, Mytilene 81100, Greece *E-mail: tevagelo@marine.aegean.gr Abstract 1 - Spatial and seasonal variations of two important biological quality elements (phytoplankton and macrobenthic invertebrates) in Transitional Water (TW) ecosystems were studied in Kalloni Saltworks, located at the island of Lesvos (NE. Aegean Sea, Greece). 2 - A total of 36 phytoplankton taxa, belonging to 5 classes, were collected in the study area during both seasonal samplings. Many of the species found in the study area are coastal/brackish waters species that are commonly encountered in transitional waters ecosystems. A substantial seasonal change in species composition, as well as in the observed trends in density and biomass variations along the salinity gradient was revealed. Blooms of Euglena acusformis, Mesodinium rubrum and phytoflagellates were recorded in the study area. 3 - A total of 43 macrobenthic invertebrates taxa, belonging to 6 major groups, were collected in the study area during both seasonal samplings. Most of the abundant macrobenthic invertebrate species in the study area were typical lagoonal or marine/estuarine species commonly occuring in coastal lagoons, whereas typical marine species gradually disappeared downstream the pond sequence. The patterns of variation of macrobenthic invertebrates' density and biomass along the salinity gradient were different between seasons, partly due to the strong dominance of Hydrobia acuta in autumn, while species richness declined along the salinity gradient in both seasons. Introduction Solar saltworks are man-made systems for the extraction of salt from seawater, by means of solar and wind evaporation. They are also coastal aquatic ecosystems of great ecological importance, as they are characterised by considerable habitat heterogeneity. They combine a spectrum of aquatic environmental types along a long salinity gradient (seawater salinity – 300 ppt). Solar saltworks are closely related to natural transitional water (TW) ecosystems, as they are located at the land – sea interface and their lower salinity part (seawater salinity – 100 ppt) presents many similarities with coastal lagoons, regarding both the abiotic environment and the biota. Phytoplankton communities have been documented in several solar saltworks due to their importance for salt production (Davis 1990), although the spatial resolution of the data in the saltworks ecosystems studied was usually low. On the other hand, community structure and ecological functions of macrobenthic invertebrates in solar saltworks ecosystems are poorly documented, as very few studies currently exist in the literature (e.g. Britton & Johnson 1987; Evagelopoulos & Koutsoubas 2007). The aim of the present paper is to outline the main trends in the variations of widely applied descriptors of phytoplankton and macrobenthic invertebrates in TW ecosystems (i.e. composition, density, biomass and phytoplankton bloom parameters; EC 2003) along the salinity gradient at the lower salinity ponds in Kalloni Saltworks, Greece.