The role of emersion time in modulating biomarker responses to pollution in intertidal mollusks

The intertidal zone is a stressful environment where organisms must develop adaptive responses to each emersion cycle. Therefore, when studying the effects of pollution on intertidal organisms, this factor should be considered. However, the interactive effects of pollution and emersion time on invertebrates at the same intertidal level remain largely unexplored. This study aimed to investigate the influence of air exposure time on the immunological and antioxidative biomarkers of two intertidal mollusk species to pollution. Limpets (Siphonaria lessoni) and mussels (Brachidontes rodriguezii) were collected from two polluted harbor sites (QQ and MDP) and a reference site (RCT) at different emersion times: 0, 2, and 4 h. Biomarkers measured included phenoloxidase (PO), alkaline phosphatase (AP), glutathione-S-transferase (GST), and catalase (CAT) activities, as well as thiobarbituric acid reactive substances (TBARs) levels. In general, individuals exposed to air showed exacerbated biomarker responses to pollution, even at the shortest emersion time (2 h). Conversely, limpets and mussels from RCT showed increased enzyme activity only after 4 h of emersion, suggesting greater resistance to emersion stress, likely due to a healthier environment. Additionally, air exposure enhanced TBARs levels in limpets (>190 % in MDP; >300 % in QQ) and mussels (>260 % in QQ) from contaminated harbor sites, while organisms from the reference site showed no such changes. Overall, the magnitude of differences between polluted and unpolluted sites was dependent on the timing of organism collection during emersion for most of the biomarkers/situations studied. Thus, our results highlight how air exposure time can confound biochemical responses to pollution, emphasizing the importance of considering emersion duration when assessing the physiological status of intertidal organisms in polluted ecosystems. These findings should be interpreted within the broader context of multiple environmental and biological factors that collectively shape pollution responses in intertidal communities.