Size-Dependent Habitat Selection in a Tropical Freshwater Crayfish: Preference for Vegetated Refugia

Habitat selection is a critical ecological process influencing survival and recruitment during early life stages of freshwater species, yet it remains unclear whether observed habitat use reflects active preference or simple accessibility. We experimentally quantified habitat selection in the freshwater crayfish Cherax quadricarinatus across two early life stages (craylings and juveniles), testing whether individuals actively select structurally complex habitats and whether this selection is size-dependent. Using laboratory choice and no-choice arenas, we found that both life stages exhibited clear, measurable preferences for vegetated habitats. Craylings selected vegetation 10.7% ± 3.44% more often when choice was available compared with no-choice conditions, while juveniles showed a markedly stronger response, selecting vegetation 60.0% ± 9.03% more often. In contrast, use of sand declined under choice conditions (craylings: -12.0% ± 4.59%; juveniles: -6.67% ± 15.87%), and gravel showed little or no positive selection (craylings: 2.7% ± 6.64%; juveniles: 0% ± 9.03%). Habitat use in no-choice arenas was comparatively even, indicating that accessibility alone could not explain observed patterns. Together, these results demonstrate that vegetated habitats provide disproportionately important refuge for early life stages of freshwater crayfish, with juveniles exhibiting five‑ to sixfold stronger selection for vegetation than craylings. Our findings highlight how the loss of habitat complexity through environmental change or anthropogenic disturbance may reduce recruitment success and population viability in tropical freshwater ecosystems.