Adopting and adapting macroinvertebrate measures for health assessments of ephemeral freshwater systems : a review

Ephemeral streams are waterways with poorly defined channels and episodic flow. Globally, the occurrence of ephemeral streams appears to be increasing due to drying trends driven by climate change, as well as a result of increased water abstraction. Simultaneously, these pressures result in increased vulnerability of ephemeral streams, as flow rates decline from intermittent to entirely absent. Despite this, ephemeral waterways are broadly neglected by ecologists, and no tailored measures are available to study the health of these systems. Traditional assessment methods applied to lotic or lentic environments include physicochemical analyses, often paired with the use of biological indicators. Due to abundance and diversity, sensitivity to changes in flow, water quality and toxicity aquatic macroinvertebrates are widely used as indicators of ecological condition. However, the theoretical base underpinning the use of macroinvertebrate protocols to assess waterway condition has generally been developed from studies of temperate, permanent waterways with few studies specific to tropical or subtropical ephemeral environments. To address the knowledge gap, this review examines the current state of knowledge regarding the health of ephemeral systems, focussing on Australian freshwaters. It also examines the applicable ecosystem health measures that may be transferable to ephemeral systems, with a focus on macroinvertbrates as bioindicator species.