Salinisation reduces biodiversity in neighbouring freshwater patches in experimental metacommunities

• Published in: Freshwater biology 2020-03, Vol.65 (3), p.592-604
• Main Authors: Mausbach, William E., Dzialowski, Andrew R.
• Format: Article
• Language: English
• Subjects: Aquatic ecosystems; Biodiversity; Biodiversity hot spots; Community composition; Composition; Dispersal; Dispersion; Ecosystems; Environmental degradation; Environmental effects; Environmental stress; Fresh water; Freshwater; Freshwater ecosystems; Habitats; Heterogeneity; Inland water environment; keystone ecosystems; Mesocosms; metacommunity; Patchiness; Population decline; Populations; Saline water; Salinity; Salinity effects; Salinity gradients; Salinity tolerance; Salinization; Spatial heterogeneity; Species composition; Water quality; zooplankton
• ISSN: 0046-5070; 1365-2427
• DOI: 10.1111/fwb.13457

Aquatic ecosystems are biodiversity hot spots across many landscapes; therefore, the degradation of these habitats can lead to decreases in biodiversity across multiple scales. Salinisation is a global issue that threatens freshwater ecosystems by reducing water quality and local biodiversity. The effects of salinity on local processes have been studied extensively; however, the effects of salinisation or similar environmental stressors within a metacommunity (a dispersal network of several distinct communities) have not been explored. We tested how the spatial heterogeneity and the environmental contrast between freshwater and saline habitat patches influenced cladoceran biodiversity and species composition at local and regional scales in a metacommunity mesocosm experiment. We defined spatial heterogeneity as the proportion of freshwater to saltwater patches within the metacommunity, ranging from a freshwater‐dominated metacommunity to a saltwater‐dominated metacommunity. Environmental contrast was defined as the environmental distance between habitat patches along the salinity gradient in which low‐contrast metacommunities consisted of freshwater and low‐salinity patches and high‐contrast metacommunities consisted of freshwater and high‐salinity patches. We hypothesised that the α‐richness of freshwater patches and metacommunity γ‐richness would decrease as freshwater patches became less abundant along the spatial heterogeneity gradient in both low‐ and high‐contrast metacommunities, because there would be fewer freshwater patches that could serve as source populations for declining populations. We hypothesised that low‐contrast metacommunities would support more species across the spatial heterogeneity gradient than high‐contrast metacommunities, because, via dispersal, low‐salinity patches can support halotolerant freshwater species that can mitigate population declines in neighbouring freshwater patches, whereas` high‐salinity patches will mostly support halophilic species, providing fewer potential colonisers to freshwater patches. We found that α‐richness of freshwater mesocosms and metacommunity γ‐richness declined in saline‐dominated metacommunities regardless of the environmental contrast between the freshwater and saline mesocosms. We found that environmental contrast influenced freshwater and saline community composition in low‐contrast metacommunities by increasing the abundances of species that could tolerate low‐salinity environments throug