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Scavenging by threatened turtles regulates freshwater ecosystem health during fish kills.

ABSTRACT: Humans are increasing the frequency of fish kills by degrading freshwater ecosystems. Simultaneously, scavengers like freshwater turtles are declining globally, including in the Australian Murray-Darling Basin. Reduced scavenging may cause water quality problems impacting both ecosystems and humans. We used field and mesocosm experiments to test whether scavenging by turtles regulates water quality during simulated fish kills. In the field, we found that turtles were important scavengers of fish carrion. In mesocosms, turtles rapidly consumed carrion, and water quality in mesocosms with turtles returned to pre-fish kill levels faster than in turtle-free controls. Our experiments have important ecological implications, as they suggest that turtles are critical scavengers that regulate water quality in freshwater ecosystems. Recovery of turtle populations may be necessary to avoid the worsening of ecosystem health, particularly after fish kills, which would have devastating consequences for many freshwater species.

SUBMITTER: Santori C

PROVIDER: S-EPMC7499268 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature

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Scavenging by threatened turtles regulates freshwater ecosystem health during fish kills.

Santori Claudia C Spencer Ricky-John RJ Thompson Michael B MB Whittington Camilla M CM Burd Thomas H TH Currie Samantha B SB Finter Timothy J TJ Van Dyke James U JU

Scientific reports 20200917 1

Humans are increasing the frequency of fish kills by degrading freshwater ecosystems. Simultaneously, scavengers like freshwater turtles are declining globally, including in the Australian Murray-Darling Basin. Reduced scavenging may cause water quality problems impacting both ecosystems and humans. We used field and mesocosm experiments to test whether scavenging by turtles regulates water quality during simulated fish kills. In the field, we found that turtles were important scavengers of fish ...[more]

PMID: 32943647

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Project description:High turbidity and elevated water temperature are environmental stressors that can co-occur in freshwater ecosystems such as when deforestation increases solar radiation and sedimentary runoff. However, we have limited knowledge about their combined impacts on fish behaviour and physiology. We explored independent and interactive effects of sedimentary turbidity and temperature on the swimming activity and both thermal and hypoxia tolerance of the Pugnose Shiner (Miniellus anogenus, formerly Notropis anogenus), a small leuciscid fish listed as Threatened under Canada's Species at Risk Act (SARA). Fish underwent a 15-week acclimation to two temperatures (16°C or 25°C) crossed with two turbidities (~0 NTU or 8.5 NTU). Swimming activity was measured during the first 8 weeks of acclimation. Fish in warm water were more active compared to those in cold water, but turbidity had no effect on activity. Behavioural response to hypoxia was measured after 12 weeks of acclimation, as the oxygen level at which fish used aquatic surface respiration (ASR). Fish in warm water engaged in ASR behaviour at higher oxygen thresholds, indicating less tolerance to hypoxia. Turbidity had no effect on ASR thresholds. Finally, thermal tolerance was measured as the critical thermal maximum (CTmax) after 13-15 weeks of acclimation. Acclimation to warm water increased fish CTmax and Tag (agitation temperature) but reduced the agitation window (°C difference between Tag and CTmax) and thermal safety margin (°C difference between the acclimation temperature and CTmax). Furthermore, fish in warm, turbid water had a lower CTmax and smaller thermal safety margin than fish in warm, clear water, indicating an interaction between turbidity and temperature. This reduced thermal tolerance observed in Pugnose Shiner in warm, turbid water highlights the importance of quantifying independent and interactive effects of multiple stressors when evaluating habitat suitability and conservation strategies for imperilled species.

Dataset Information

Scavenging by threatened turtles regulates freshwater ecosystem health during fish kills.

Publications

Scavenging by threatened turtles regulates freshwater ecosystem health during fish kills.

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