Mercury Exposure and Habitat Fragmentation Affect the Movement, Foraging Behavior, and Search Efficiency of the Marsh Periwinkle (Littorina irrorata).

Abstract

The interactions between habitat fragmentation and other stressors are considered a key knowledge gap. The present study tested the hypotheses that mercury enhances the effects of fragmentation by (1) reducing the cumulative daily movement of organisms, (2) shifting their foraging behavior, and (3) altering the vertical movement of the marsh periwinkle (Littoraria irrorata) in a field experiment. Random walk simulations were used to access how changes in movement affect the search efficiency of organisms in the long term. Eighteen 1.5 m2 plots were constructed in a salt marsh where landscapes characteristics were manipulated to reach three different levels of habitat cover. Daily movement of 12 marked control and mercury-exposed snails were measured in each plot. Bayesian models were used to analyze the data and evidence ratios were used to test the hypotheses. The results showed that the effects of fragmentation were consistent in both control and exposed treatments, with an increase in the cumulative displacement of organisms. However, mercury significantly reduced the movement of organisms in all levels of fragmentation, shifting their foraging behavior (evidence ratio > 1000). Exposed snails were more likely to be found inactive in comparison with the control treatment (evidence ratio > 1000). Fragmentation also reduced the vertical movement of organisms in both treatments. In contrast, mercury increased the vertical movement of organisms (evidence ratio > 1000). The search efficiency of organisms also increased in a highly fragmentated landscape, suggesting that changes in foraging behavior are likely due to reduced resources and consequently increase in foraging effort. The present study shows that mercury exposure can enhance the effects of habitat fragmentation by changing organisms' movement, foraging behavior, and search efficiency. Environ Toxicol Chem 2023;42:1971-1981. © 2022 SETAC.