Patterns of salinity regime in coastal lakes based on structure of benthic invertebrates.

Krystian Obolewski,Natalia Mrozińska,Aleksander Astel,Katarzyna Glińska-Lewczuk,Monika Szymańska,Ewa Paturej,Sylwia Lew,Martyna Bąkowska,Miguel Cañedo-Argüelles Iglesias

doi:10.1371/journal.pone.0207825

Abstract

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.

Highlights

Recent studies on the structure of benthic invertebrate communities have reported regime shifts in ecosystems [1, 2]
Non-metric multidimensional scaling (NMDS) revealed remarkable differences in environmental conditions, mostly in salinity and concentrations of chlorides and sodium, which resulted from the influx of seawater to the coastal lakes (Fig 2A)
Mean Secchi depth in the studied lakes was about 0.3 m and it increased with salinity, in contrast to water temperature

Summary

Introduction

Recent studies on the structure of benthic invertebrate communities have reported regime shifts in ecosystems [1, 2]. Salinity regime and structure of the bottom fauna abundance is low, very much like the proportion of predatory fish and Z:P ratio [7] This approach is extended to other lake types, including coastal water bodies varying in the degree of hydrological connection with the sea and, in salinity [8]. Coastal freshwater and brackish water bodies are important ecotones worldwide, more and more often threatened by human impact, including the rising sea level and activity of the increasing human population [9, 10] Because of their geographic location between the sea and land, lagoons and coastal lakes are the most productive and complicated marine ecosystems [11]. There is relatively little information on ecosystems with periodical intrusion, as dynamic systems, where reaching a permanent balance is impossible according to the theory of ecosystem resilience [15]

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