Sensitivity of freshwater species under single and multigenerational exposure to seawater intrusion

Abstract

Salinization of coastal freshwater ecosystems is already occurring in some regions of the world. This phenomenon raises serious concerns on the protection of coastal freshwater ecosystems, since many of them support and shelter a large number of species and are considered hotspots of biodiversity. This work intended to assess the adverse effects that salinization, caused by the intrusion of seawater (SW), may pose to freshwater organisms. In this study, three specific goals were addressed: (i) to assess if sodium chloride (NaCl) may be used as a surrogate of natural SW at early-stages of risk assessment; (ii) to identify the most sensitive freshwater species to salinity NaCl; and (iii) to determine if increased tolerance to salinity may be acquired after multigenerational exposure to low levels of salinization (induced with NaCl). A total of 12 standard monospecific bioassays were carried out by exposing organisms from different taxonomic groups (Cyanobacteria: one species, Tracheophyta: two species, Rotifera: one species, Arthropoda: two species and Mollusca: one species) to a series of concentrations of NaCl (ranging from 0.95 to 22.8 mS cm –1 ) or dilutions of SW (ranging from 1.70 to 52.3 mS cm −1 ). In general, NaCl exerted similar or higher toxicity than SW, both at lethal and sublethal levels, suggesting that it may be proposed as a protective surrogate of SW for first tiers of salinization risk assessment. Among all tested species, the cyanobacterium Cylindrospermopsis raciborskii , the daphnid Daphnia longispina and the rotifer Brachionus plicatilis were the most sensitive taxa to salinization (EC 50 ≤ 4.38 mS cm −1 ). Given their position at the basis of the food web, it is suggested that small increments of salinity may be enough to induce structural changes in freshwater communities or induce changes in trophic relations. No clear evidences of increased tolerance after multigenerational exposure to low levels of salinity were found. This article is part of the theme issue ‘Salt in freshwaters: causes, ecological consequences and future prospects’.

Combined salinity and acidity stressors alterDaphnia magnapopulation growth and structure under severe absence of photoperiod

“…This relates to halotolerance in D. magna [92] which may have contributed to resilience in the Daphnia lineage to the severity of salinity over time in this experiment. However, as freshwater salinisation significantly contributes to biodiversity loss and alteration of ecosystem functioning [93,94], acute and elevated levels of salinity can be detrimental to Daphnia [92].…”

Exposure to salinity stress cause ovarian disruption in a stenohaline freshwater teleost, Heteropneustes fossilis (Bloch, 1794)

“…Alteration in any abiotic factors such as temperature, photoperiod, pH, dissolved oxygen and salinity of aquatic ecosystem due to global climate change and anthropogenic activities affect homoeostasis of aquatic organisms dwell in that habitat (Acharjee, Chaube, & Joy, ; Eissa & Zaki, ; Hyatt, Anderson, & O’Dommell, ; Venancio et al, ). Amongst them, salinity is a key abiotic stressor to cause significant changes in various physiological traits as well as in species composition of aquatic bodies (Bosker, Santoro, & Melvin, ; Canedo‐Arguelles et al, ; Lehtonen, Wong, & Kvarnemo, ; Wedderburn, Barnes, & Hillyard, ).…”

“…Salinization of freshwater aquatic bodies may be due to several impacts of climate change, such as flooding and invasion of seawater, drought, precipitation and evaporation of water during seasonal variations. Human activities, such as agriculture and salt mining are also increasing saline concentrations in inland freshwater (Venancio et al, ). Salinity heavily affects the overall homoeostasis of both euryhaline and stenohaline fish (Acharjee et al, ; Ahmmed et al, ; Hyatt et al, ; Lisboa, Barcarolli, Sampaio, & Bianchini, ).…”

Geographical origin determines responses to salinity of Mediterranean caddisflies

“…Rivers from Mediterranean Chile are characterized by strong 27 environmental gradients [20][21][22], where both altitude and latitude are strong predictors 28 of abiotic conditions. 29 Besides this, hydrological basins in this region have been threatened by economic 30 activities mainly derived from mining and agriculture industry during the last century. 31 These actions have disrupted physical, chemical and biological properties of these 32 ecosystems [4,23].…”

“…In the current scenario of fast temporal and spatial changes in water levels and salt concentration, the conservation of geographic intra-specific variation of aquatic species is crucial for lowering the risk of salinity-driven biodiversity loss. 60 freshwater organisms are negatively affected by increased salinity [28,29]. According to 61 this hypothesis, we would expect that low-salinity adapted organisms will be more 62 July 11, 2019 2/10 130 exhibition of any given behavior, here referred as "activity" was analyzed using a model 131 which included body size, the time at measurement as well as the kind of behavioral 132 trait adopted in each activity event recorded at each experimental condition.…”