Canal construction disrupts background matching 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 their 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: 10.29 ± 5.475; P. bidens: 12.61 ± 4.832) compared to
natural habitats (P. pictum: 7.465 ± 3.855, Z = -7.698,
P < 0.001; P. bidens: 9.512 ± 4.226, Z = -11.680,
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 likely increases predation risk and represents a significant
anthropogenic threat to benthic fauna. Our research provides a critical
assessment of how human infrastructure compromises adaptive camouflage,
offering vital insights for the conservation management of estuarine
biodiversity.