Effects of Turbidity and Acidity on Predator-Prey Interactions

Abstract

Predator-prey interactions are influenced by environmental condition changes, such as increased turbidity and acidification caused by human disturbance. These anthropogenic factors can affect trophic interactions from pisciovorous fish, invertivorous fish, and shredder invertebrates to leaf litter leaching. In this study, we investigated effects of increased turbidity and acidification on predator-prey interaction through a four-level detritus-based food chain, which are top predator (pisciovorous fish), intermediate predator (invertivorous fish), shredder invertebrates, and allochthonous leaf litter. The experiment had a top predator-snakehead (Channa argus), an intermediate predator-black carp (Mylopharyngodon piceus), shredder prey-a freshwater crustacean isopods (Asellus sp.), and allochthonous leaf litter sakura (Cerasus sp.). The pisciovorous snakehead was caged, providing non-lethal predation effect on black carp. The effects of turbidity condition changes with different Nephelometric Turbidity Unit (high level: 60 NTU, and low: 10 NTU) and acidic condition changes (weakly acidic: pH 6.0 and normal: pH 7.5) on leaf litter weight loss. The experiment measured shredder density change and leaf litter weight change that was caused by both leaf litter leaching and shredder’s foraging processes. Results indicated that: the high turbid treatment (60 NTU) reduced the black carp’s antipredator defense to snakehead, so that the black carp’s foraging caused the high mortality of isopod shredders, which reduced leaf litter weight loss. By contrast, the weakly acidic treatment (pH=6.0) did not influence black carp’s top-predator avoidance, but induced the loss of predator avoidance of isopod Asellus sp. shredders that caused isopod high mortality. The acidic treatment did not influence litter weight change. Our study highlights that increased turbidity can influence predator-prey interactions and affect leaf litter weight change that caused by both shredder foraging and litter leaching processes in freshwater systems. The increased acidic condition also had a significant effect on predator-prey interaction. With intensified urbanization and increased climate change, such anthropogenic impacts with multiple stressors on predator-prey interaction should be further investigated for understanding their ecological mechanisms.