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The macrozoobenthic diversity patterns along a brackish–freshwater salinity gradient have been identified, considering effects of differences in the level of hydrological connection of coastal lakes with the sea on the structure of benthic invertebrate communities. The study is based on samples from six coastal lakes located along the southern coast of the Baltic Sea in Poland. The analysis of environmental and biological data confirmed the existence of stable phases (brackish water vs. freshwater), but as a result of periodical intrusion of seawater, adaptation of animal communities takes place, which was reflected in low values of the predictors describing them (number of taxa, density and diversity). Redundancy analysis indicates that values of conductivity and salinity are the major factors that determine the abundance of dominant groups of benthic fauna. The gradient of hydrological connection of the lakes with the sea accounted for 50% of the variance in biological data, physico-chemical variables for 25%, trophic variables for 15%, and only 9% of the variance was unexplained. The major implication of our results is that coastal lakes that differ only slightly in salinity can have alternative, regional patterns of diversity of structure of benthic fauna. Periodical inflow of brackish waters initiates adaptive cycles of benthic fauna, and their frequency is strongly linked with the hydrological regime. The rhythm of the inflow of seawater is variable, so that management and protection of coastal lakes are extremely complicated. [ABSTRACT FROM AUTHOR]

The species composition and abundance of epiphytic fauna inhabiting common reed ( Phragmites australis (Cav.) Trin. ex Steud.) was performed in five coastal lakes in Słowiński National Park (southern Baltic coast in northern Poland). The lakes represent a salinity gradient (from freshwater to β-oligohaline waters) and four types of coastal lakes: (1) lagoon, L (Lake Łebsko, seawater enters it permanently); (2) coastal lake with periodically brackish water, CLB (Lake Gardno); (3) freshwater costal lake, CLF (Lake Smołdzińskie); and (4) coastal dune lakes, CLD (Dołgie Wielkie and Dołgie Małe). Using statistical ordination techniques, we found that the structure of epiphytic fauna (microinvertebrates and macroinvertebrates) is determined primarily by hydrological connectivity (water exchange) with the sea. Canonical Correspondence Analysis, coupled with variance partitioning, showed that hydrological connectivity accounted for 24% of the variation in the invertebrate community, followed by physico-chemical (19%) and trophic (8%) factors. Our results indicate that the assemblages of Ciliata-libera and Cnidaria are characteristic for L (β-oligohaline), Rotifera, Suctoria, Chaetogaster sp., Gastropoda and Trichoptera are characteristic for CLB (limnetic/β-oligohaline), but no taxonomic groups are characteristic for CLF and CLD (both limnetic). The index of multivariate dispersion showed a decreasing trend with the increasing lake isolation from the open sea, except for CLD. However, in terms of the structure of epiphytic fauna, Multi-Response Permutation Procedures showed that CLD significantly differed only from CLB. Our results suggest that the identified characteristic taxonomic groups of plant-associated macroinvertebrates have a high potential to be used as bioindicators of salinity and water exchange with the sea, due to their sensitivity to environmental stress. [ABSTRACT FROM AUTHOR]

The study was aimed to analyse reactions of the major groups of phytoplankton to the mixing regime of fresh and brackish waters in coastal lakes and the associated changes in physicochemical properties of lake waters. For this purpose, on the basis of data collected from 6 coastal lakes located along the southern coast of the Baltic Sea, differing in intensity of intrusion of brackish sea water: limnetic, L (2), limnetic/oligohaline, L/O (2), and oligohaline, O (2), we assessed the associations of major phytoplankton groups with environmental conditions. Statistical analyses revealed that the structure of phytoplankton groups significantly differed among three lakes types, and the variation in these variables was best explained by water temperature, total phosphorus, salinity, PO 4 3− , transparency, dissolved oxygen, and NO 3 − . Relative phytoplankton biomass showed significant differences among the O–L/O–L lake types and formed the following proportion 1:2:3.5. Cyanobacteria constituted a dominant algae group in the lakes, showing the decreasing trend from 86.5% in the L to 69.3% in the O lakes. The indicator value analysis showed that all the studied lakes were dominated by algae preferring freshwater habitats, among which Cyanobacteria and Cryptophyta were indicator groups. Redundancy analysis showed that increasing salinity has got a negative effect on Cyanobacteria and Bacillariophyta biomass, and did not stimulate the development of any algal group. In the coastal lakes we observed 2 distinct stable states (limnetic and oligohaline) as well as transitional phases between them: (1) seaward drift (limnetic-oligohaline) with increasing salinity, and (2) landward drift (oligohaline-limnetic) with decreasing salinity. Algal communities showed the most distinct differences in biomass in limnetic and oligohaline states. These observations suggest that the structure and biomass of phytoplankton may respond gradually on the level of hydrological connectivity, or may respond abruptly creating two alternative stable states: limnetic and oligohaline. [ABSTRACT FROM AUTHOR]