Salinity as a Key Factor on the Benthic Fauna Diversity in the Coastal Lakes

Abstract

Benthic communities were studied in nine Polish coastal lakes of the Baltic Sea; representing three levels of hydrological connection with the sea (isolated, periodically connected, and permanently connected), with resultant differences in salinity (freshwater, transitional, and brackish). The lakes classified in this way allowed us to investigate biodiversity in relation to the degree of environmental pressure. Stress intensity in coastal water bodies, resulting from contrasting marine and terrestrial influences, varied from mild to severe. Spatial variation in environmental predictors affected species richness more strongly than seasonal fluctuations. The broader the spatial salinity gradient, the smaller the species number recorded. Differences in the intensity of natural instability only slightly affected species number and α-diversity. In Baltic coastal lakes, characterized by low salinity (max. 7.5 PSU), benthic faunal communities were dominated by large populations of opportunistic species. This applied primarily to closed systems and those periodically influenced by seawater intrusion. The marine component of fauna played a more important role in increasing the diversity of benthos in permanently open water bodies (brackish). The highest density of benthic fauna was recorded in them, whereas low values were associated with the strongest instability, observed in lakes periodically linked with the sea (transitional).

Structural diagnosis of benthic invertebrate communities in relation to salinity gradient in Baltic coastal lake ecosystems using biological trait analysis

“…The data on taxa and their abundances in the studied BCLs were obtained from an open-access dataset published in studies by 45 , where sampling methods and identification procedures were also included. We had to exclude Oligochaeta and Chironomus n. det, as it is impossible to describe their characteristics precisely.…”

Physicochemical characteristics of lakes along the southern Baltic Sea coast

“…The Baltic coastal lakes can be divided into three main types: (1) open: with permanent connection to the sea through channels/river mouths; (2) intermittently connected: with periodic inflow of seawater thanks to the unblocking of buried channels; and (3) closed: permanently isolated; as well as several subtypes 5 . This hydrological connectivity leads to a variable exchange of substances between the individual ecosystem types, which influences their ecological status depending on the predominance of the marine or terrestrial factor 6 – 8 . The evaluation of the functioning of microhabitats shaped by the mixing of fresh and brackish water must be based on deterministic chaos theory.…”

“…Nevertheless, the constant salinity of the southern Baltic Sea (7-8 PSU) leads to the presence of stenohaline organisms, while the salinity in the lakes is generally lower and fluctuates, favoring euryhaline organisms. Therefore, the periodic increase in seawater salinity creates a “window of opportunity” effect for the immigration of marine organisms into the lakes 8 . Among others, there are: the phenomenon of backwash and brackish water intrusion, which causes a periodic change in water quality; the phenomenon of wind support, which hinders or even prevents the outflow of land water into the sea; and the phenomenon of water accumulation on the southern coasts of the Baltic Sea, which is particularly clear during autumn and winter storms.…”

“…Coastal lakes and lagoons, characterized by their unique biotopes, have attracted intensive scientific study for many years due to their significant differences in physical and chemical factors 8 , 20 , 21 . This variety is mirrored in their relatively high species diversity.…”

Determinant Drivers for the Community Structure of Benthic Macroinvertebrates in Coastal Lagoons at the Restinga De Jurubatiba National Park, in the State of Rio De Janeiro State (Brazil)

“…Studies have shown that salinity is a stress factor for benthic invertebrates (Piscart 2005, Obolewski 2018, Mrozinska 2021. According to those authors, the increase in the salinity gradient generally results in a decreasing trend in the richness and abundance of benthic species, due to the greater instability of environmental conditions in lagoons with marine intrusions.…”