Crab carapace shape as a biomarker of salt marsh metals pollution

Coastal environmental pollution is a global problem that has been growing for decades. For this reason, different approaches have been sought to address and detect its environmental implications. Some organisms are considered bioindicators or biomonitors of contamination, which provide information about environmental quality. Previous studies used the crab Neoelice granulata (Brachyura, Varunidae) as bioindicator of the presence of metals by the analysis of soft tissues to evaluate physiological and molecular markers. However, the contaminant levels accumulated in these soft tissues have shown to be affected by seasonal variations, suggesting that environmental assessments based on soft tissue samples may be unreliable. Within this framework, we aimed to describe the crab body (carapace) variations related to a known soil metal gradient in a Patagonian salt marsh and to evaluate the use of the body shape as an alternative biomarker for monitoring the quality of salt marsh systems. We studied the carapace shape variations using geometric morphometrics (GM) based on a 2D structure with object symmetry. We observed symmetric and asymmetric components of carapace shape variation. While the latter was not found associated with a gradient of contamination by metals, the symmetric component responded to environmental changes; therefore, it could be considered a stress biomarker related to metal contamination. Consequently, we recommended using GM analysis because it is inexpensive, faster and non-seasonal and could be used on living organisms, avoiding destroying individuals to measure the environmental stress.