Canal Construction Disrupts Camouflage in Two Sympatric Estuarine Crab Species

Estuarine ecosystems provide essential habitats for fiddler crabs, whose survival heavily relies on background-matching camouflage. Anthropogenic modifications such as canal construction can alter the visual properties of these habitats, yet direct empirical evidence of its impact on crustacean camouflage remains limited. This study investigated the effects of habitat canalization on the camouflage effectiveness of two sympatric crab species, Parasesarma pictum and Perisesarma bidens. We quantified color matching using the chromatic just noticeable difference (CJND) metric, comparing individuals in engineered canal habitats versus adjacent natural mudflats. Results demonstrated a significant reduction in camouflage efficacy in canalized areas for both species. The CJND values were markedly higher in canal habitats (P. pictum: 9.035(8.448); P. bidens: 12.410(6.730)) compared to natural habitats (P. pictum: 6.505(4.753), Z = -7.696, p < 0.001; P. bidens: 8.625(5.658), Z = -11.678, p < 0.001), indicating a substantial decrease in body-background color matching. Although the differences in luminance, pattern energy, and disruptive rate did not show the same trend, the weakening of color matching caused by the habitat alteration resulting from canal construction would also have a negative impact on the camouflage of the two crab species. These findings suggest that canalization alters substrate coloration and optical properties, thereby impairing the crabs' background-matching camouflage. This sensory disruption may potentially increase predation risk and could represent an anthropogenic threat to benthic fauna. Our research offers an assessment of how human infrastructure might compromise adaptive camouflage, providing insights that may be useful for the conservation management of estuarine biodiversity.