Introduction

Most waterbodies in arid regions hold water on a seasonal or episodic basis, yet they often support a diverse and unique aquatic fauna (Timms 2008). These environments are dominated by aquatic macroinvertebrates with desiccation‐resistant life stages that can persist through dry periods and may remain viable for decades or longer (Radzikowski 2013). Such diapausic and quiescent strategies typically consist of eggs or larval/nauplii stages, which form ‘egg banks’ that allow populations to re‐establish after re‐inundation (Pinceel et al. 2021). Egg banks in temporary waterbodies are dominated by crustaceans, including anostracans, cladocerans, ostracods, diplostracans and copepods (Lawrie et al. 2021; Rahman et al. 2022; Schwentner et al. 2015; Timms 2014).

Salt lakes (non‐marine enclosed bodies of water with salinities greater than 3 g/L; Bayly and Williams 1966) account for almost half (~44%) of the volume of inland waters on the planet (Messager et al. 2016) and occur on every continent (Hammer 1986). Indeed, salt lakes constitute the majority of the inland lentic waters of Australia and are particularly conspicuous in the arid zone, where vast salt lake playas have formed in the residual depressions of paleo‐drainage channels (Timms 2008; Timms et al. 2006; van de Graaff 1977). A community of specialised terrestrial macroinvertebrates has evolved to occupy these dry lake beds (Framenau and Hudson 2017; López‐López et al. 2016; Schultheiss et al. 2013) as filling events are rare and unpredictable, typically limited to rainfall from ex‐tropical cyclones (Gregory et al. 2009). After inundation, the emergence of the dormant aquatic macroinvertebrate taxa transforms these salt lakes into enormously productive ecosystems that can attract thousands of waterfowl, some of which are dependent on these remote salt lakes for breeding (Pedler et al. 2014; Pedler et al. 2018).

Relative to salt‐lake environments globally (Saccò et al. 2021), a diverse and overwhelmingly endemic suite of aquatic macroinvertebrate fauna occurs in Australian salt lakes (Lawrie et al. 2021). While our understanding of the extent of this biodiversity has improved (Islam et al. 2024; Lawrie, Chaplin, Kirkendale, et al. 2023; Lawrie et al. 2025; Meusel and Schwentner 2017; Pinceel et al. 2013; Rahman, Chaplin, Lawrie, Islam, and Pinder 2025), salt lakes in the arid Australian interior remain poorly surveyed due to logistical challenges as a result of remoteness and infrequent filling regimes (Lawrie et al. 2021; Williams 2000). Opportunistic surveys during filling events may also only encompass a subset of the community composition present because species assemblages shift from a relatively diverse suite of hyposaline taxa shortly after the initial filling event into a restricted set of hypersaline species as evaporation increases (Timms et al. 2006). Regardless, given filling events are uncommon, the aquatic biodiversity of these environments is mostly surveyed and monitored using ‘rehydration trials’ where water is artificially added to collected sediment to hatch out the egg bank under controlled laboratory conditions (Campagna 2007).

Rehydration trials assume that the artificial hatching conditions provided in the laboratory will meet the hatching requirements for all taxa present and infer that the taxa observed are representative of the fauna present under natural filling conditions. However, given it is difficult to replicate natural conditions in the laboratory and specific cues for emergence for these macroinvertebrates remain poorly studied, the suite of species recovered may not necessarily be representative of the species composition present during lake inundation events (Brendonck 1996). Once taxa have emerged, they are collected, sorted, and identified to varying levels of taxonomic resolution, largely dependent on the available taxonomic expertise. This is a time‐intensive process which requires a high degree of taxonomic proficiency with identifications prone to misclassifications (Stribling et al. 2008), particularly in cryptically diverse, microscopic groups (Pfrender et al. 2010).

Bulk DNA metabarcoding of egg banks in sediments could provide a complementary method to rehydration trials for surveying aquatic macroinvertebrate biodiversity in dry salt lakes (Rahman, Chaplin, Lawrie, and Pinder 2025). DNA metabarcoding identifies multiple species from mixed DNA samples by targeting short, taxonomically informative gene regions with high‐throughput sequencing. However, the reliability and consistency of metabarcoding data are highly dependent on optimised sample collection and preprocessing protocols (Alberdi et al. 2018; Zinger et al. 2019). In particular, direct DNA extraction from unprocessed sediments often yields poor recovery of aquatic macroinvertebrates due to a combination of unspecific primer bonding, predominance of non‐target DNA, presence of inhibitors, and the limited mass of sediment used for extraction (Pawlowski et al. 2022). One strategy to improve target detection is to isolate the biological material from sediments prior to DNA extraction using density‐based separation. For example, resting macroinvertebrate eggs can be separated from sediments by mixing concentrated sucrose solutions (sugar flotation method; Onbé 1978) with sediment samples causing the less‐dense organic material (e.g., resting stages) to float out of the largely mineralised sediments (Briski et al. 2013). Sugar‐flotation has previously been used in conjunction with single species DNA barcoding (Briski et al. 2011) and for metabarcoding of the sediments from a permanent freshwater lake (Wang et al. 2020), but its efficacy for surveying aquatic macroinvertebrates in dry lakes remains undetermined.

Here we evaluate the utility of DNA bulk metabarcoding to survey the biodiversity of aquatic macroinvertebrates of dry sediments from an Australian salt lake via two complementary experiments. Experiment 1 tested whether elutriating sediments through sugar‐flotation improves the detection of aquatic macroinvertebrates compared to DNA extraction from unaltered sediment (hereafter the standard sediment method). Experiment 2 examined how sediment weight influences recovered species richness and community composition of aquatic macroinvertebrates by comparing four sugar‐floated sediment weights (50, 250, 500 and 1000 g). The hypothesis is that the observed species richness will increase with sediment weight, while the variation in community composition between replicates within a treatment will decrease. Finally, DNA metabarcoding results from the 1000 g samples from Experiment 2 were compared against taxa recovered from rehydration trials from the same sediment samples to evaluate the strengths and limitations of each method for surveying dry salt lakes.