Published Research
PEER REVIEWED JOURNAL ARTICLES
June 28 2024, Southern Cross University
Thermal challenges for stream invertebrate assemblages and species - insights into impacts of extreme wildfires
Abstract
The frequency and intensity of extreme wildfire events have increased globally. The impact of extreme wildfires on stream temperatures and subsequent stream invertebrate survival is not well understood and very few studies have focused on temperature spikes during the combustion phase of these wildfire. Stream invertebrates are essential for maintaining the overall health and functions of stream ecosystems. However, as ectotherms, stream invertebrates are vulnerable to increasing temperatures, dying from heat stress when lethal thresholds are exceeded.
This thesis investigates the immediate response of stream invertebrates to acute short-term stream temperature spikes, specifically those resembling spikes caused during the combustion phase of extreme wildfire events. The research examined stream invertebrate mortality, population changes, and overall ecosystem resilience during and immediately after simulated acute short-term extreme temperature events. The first component of this research used highly controlled laboratory mesocosm temperature disturbance experiments to explore the effects of 45°C and 55°C acute short-term temperature spikes on natural stream invertebrate assemblage. The results showed that a 55°C temperature spike caused a 95.9% reduction in abundance and functional feeding group diversity was reduced to scrapers and shredders. Conversely, the 45°C temperature spike had no significant impact on either abundance or richness of functional feeding groups. Individual families responded differently to the temperature spike, with some families being very sensitive to the increase in temperature and two being tolerant of the spike and the resulting reduction in abundance and diversity will influence post fire recovery.
The second component of this thesis investigated, for the first time, the specific Upper Lethal Temperature (ULT) (LT50) of five Australian subtropical stream invertebrate taxa (four species and one genus). These taxa were chosen based on their identified sensitivity or tolerance to higher temperatures observed during the mesocosm experiments. The aim was to gain insights into the lethal thresholds of these taxa in response to temperature extremes. The ULTs ranged from 35.2°C for the shrimp <em>Paratya spinosa</em> to 37.2°C for the adult beetle <em>Macrogyrus oblongus. The ULTs were all below the temperature spikes of 55°C and 45°C investigated in the mesocosm experiments. The results highlight the importance of refugia areas in stream ecosystems. The availability and maintenance of thermal refugia, such as the hyporheic zone, play a fundamental role in providing shelter and buffering against extreme water temperatures for stream invertebrates. Invertebrates inhabiting subtropical streams appear to be living closer to their ULT than those identified in previous studies in temperate zones, making them more susceptible to extreme heat events. Finally, the thesis explored the potential for the thermal plasticity of the shrimp <em>Paratya</em> spp. as an adaptive mechanism in response to changing thermal conditions. Results showed warm-water acclimated shrimp had a significantly higher LT50 of 36.1°C than winter acclimated shrimp at 34.6°C. <em>Paratya</em> spp. had a potential critical temperature (LT90) of ~37°C, beyond which the shrimp could not survive. This critical limit underscores the vulnerability of <em>Paratya</em> spp. to extreme heat events and highlights the need for more understanding of the impacts of increasing stream temperatures.
The research completed in this thesis helps to fill gaps in knowledge by evaluating stream invertebrate assemblage dynamics and providing insights into lethal temperature thresholds for different taxa. It also highlights the potential for adaptive responses and resilience in stream ecosystems. This research thesis improves and enhances our knowledge of the vulnerability of stream invertebrates to extreme water temperature spikes and future thermal extreme events.
March 14 2023, Marine and Freshwater Research
Plasticity of upper thermal limits of Australian Paratya spp. (Decapoda, Atyidae) and considerations of climate-change adaptation
Abstract
Context: The ability of ectothermic stream invertebrates to adapt to the predicted increases in mean and extreme stream temperatures is crucial to ensuring they continue to exist.
Aims: To examine the plasticity of thermal limits of Australian Paratya spp. (Decapoda, Atyidae) from streams in eastern New South Wales (NSW). We hypothesised that the upper lethal temperature (ULT, as indicated by the median lethal temperature, LT50) would be higher for warm water-acclimated shrimp individuals than for winter-acclimatised shrimp individuals because of the importance of acclimatisation temperature.
Methods: Controlled experiments were undertaken to determine the ULT by using ramping assays for winter field-acclimatised and warm water laboratory-acclimated Paratya spp.
Key results: Warm water-acclimated shrimp individuals demonstrated a significantly higher LT50 of 36.1°C than did winter-acclimatised shrimp individuals at 34.6°C. Paratya spp. exhibited a limited plasticity for acclimation to warmer temperatures.
Conclusions: Results demonstrated the potential vulnerability of ectothermic stream invertebrates to climate change if stream temperatures increase as predicted and thermal thresholds are exceeded.
Implications: Understanding the ULT of stream invertebrates helps predict their ability to respond to temperature variability and response to climate change. Increasing resilience through target management of resorting riparian vegetation for shade and securing environmental flows may reduce the impacts of stream warming.
Keywords: acclimatisation, climate change, distribution, macroinvertebrates, plasticity, shrimp, stream temperature, thermal tolerance.
In peer review
Mixing Fire and Water: Consequences of High-Severity Wildfires for Riverine Ecosystems
Brendan G. Cox, Andrew J. Brooks, William Bovil, Catherine Leigh, Pauline F. Grierson, Ewen Silvester, Michael Reid, Mark Lintermans8, Ben J. Kefford, Ross M.Thompson, Alec Davie, Sarah Mika, Sally MaxwelL, Lisa J. Evans, and Ryan M. Burrows.
Abstract
Riverine ecosystems are among the most threatened ecosystems globally. Exposure to increased frequency and spatial extent of high-severity wildfires are amongst the most serious threats facing riverine ecosystems. High severity fires are increasingly being referred to as high-severity ‘megafires’. The ecological consequences of these fires are poorly understood. Still, they may include effects on important riverine ecosystem functions, patterns in diversity across a range of scales and habitats, and their potential recovery trajectories. Here, we identify themes that provide a conceptual framework for understanding the consequences of high-severity wildfire on riverine ecosystems and their subsequent recovery. In particular, we illustrate how different aspects of the fire regime and the location of a fire can affect both the ecological responses and interactions among the terrestrial impacts and riverine ecosystem consequences. We highlight gaps in knowledge to motivate a hypothesis-driven research program focused on understanding ecosystem consequences and recovery in riverine ecosystems due to high-severity wildfires.
Keywords: Megafire, climate change, water quality, biodiversity, ecosystem recovery
November, 2019 Ecological Indicators Volume 106
A comparison of macroinvertebrate-based indices for biological assessment of river health: A case example from the sub-tropical Richmond River Catchment in northeast New South Wales, Australia
Brendan Cox, Sue Oeding, and Kathryn Taffs,
ABSTRACT
Globally, river health is deteriorating due to increased anthropogenic pressures. Accurately assessing river health is crucial for the management of river resources with macroinvertebrates commonly used as biological indicators of ecological integrity. Complex biological data is made more straightforward using indices as they offer the ability to rapidly communicate complex science in a simple form. Management decisions are often based on the results of biological river health assessments, making the identification of the most appropriate, robust and sensitive macroinvertebrate-based index vital when undertaking catchment specific assessments. Selection of a macroinvertebrate-based index should rely on a scientific method rather than arbitrary selection criteria. This study aimed to compare the performance of several macroinvertebrate-based indices to identify the index or indices most appropriate to the Richmond River Catchment (RRC) in northern New South Wales, Australia. River health within the RRC is poor with a clear pollution gradient from upper to lower catchment sites. Six commonly used indices were calculated using family-level identification. The biological assessment supported the physicochemical results with a gradient in river health from upper to lower catchment. Family Richness and Family Richness Percent were assessed as the most usable indices. In studies that have restricted time, budget and expertise they will provide accurate but limited information on river health. SIGNAL2 was identified as the most valid index for assessing river health due to its overall sensitivity to changes in river health, and level of detail on anthropogenic impacts. The poor performance of the AUSRIVAS, EPT and BCI limits or precludes their use for river health assessment in the RRC. While this model for identification and selection of an appropriate macroinvertebrate-based index for catchment scale river health assessments was useful in this context, it needs to be improved with a larger dataset and a greater environmental gradient of river health to make a less subjective evaluation.
15 January, 2018. Journal of Environmental Management, Volume 206
The influence of land use in a highly modified catchment: Investigating the importance of scale in riverine health assessment
Oeding, S., Taffs, K.H., Cox, B., Reichelt-Brushett, A., Sullivan, C.
ABSTRACT
Globally, river health is deteriorating due to increased anthropogenic pressures. Accurately assessing river health is crucial for the management of river resources with macroinvertebrates commonly used as biological indicators of ecological integrity. Complex biological data is made more straightforward using indices as they offer the ability to rapidly communicate complex science in a simple form. Management decisions are often based on the results of biological river health assessments, making the identification of the most appropriate, robust and sensitive macroinvertebrate-based index vital when undertaking catchment specific assessments. Selection of a macroinvertebrate-based index should rely on a scientific method rather than arbitrary selection criteria. This study aimed to compare the performance of several macroinvertebrate-based indices to identify the index or indices most appropriate to the Richmond River Catchment (RRC) in northern New South Wales, Australia. River health within the RRC is poor with a clear pollution gradient from upper to lower catchment sites. Six commonly used indices were calculated using family-level identification. The biological assessment supported the physicochemical results with a gradient in river health from upper to lower catchment. Family Richness and Family Richness Percent were assessed as the most usable indices. In studies that have restricted time, budget and expertise they will provide accurate but limited information on river health. SIGNAL2 was identified as the most valid index for assessing river health due to its overall sensitivity to changes in river health, and level of detail on anthropogenic impacts. The poor performance of the AUSRIVAS, EPT and BCI limits or precludes their use for river health assessment in the RRC. While this model for identification and selection of an appropriate macroinvertebrate-based index for catchment scale river health assessments was useful in this context, it needs to be improved with a larger dataset and a greater environmental gradient of river health to make a less subjective evaluation.