Effects of Turbidity on Prey Selection and Foraging Return of Adult Largemouth Bass in Reservoirs (original) (raw)
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Turbidity interferes with foraging success of visual but not chemosensory predators
Predation can significantly affect prey populations and communities, but predator effects can be attenuated when abiotic conditions interfere with foraging activities. In estuarine communities, turbidity can affect species richness and abundance and is changing in many areas because of coastal development. Many fish species are less efficient foragers in turbid waters, and previous research revealed that in elevated turbidity, fish are less abundant whereas crabs and shrimp are more abundant. We hypothesized that turbidity altered predatory interactions in estuaries by interfering with visually-foraging predators and prey but not with organisms relying on chemoreception. We measured the effects of turbidity on the predation rates of two model predators: a visual predator (pinfish, Lagodon rhomboides) and a chemosensory predator (blue crabs, Callinectes sapidus) in clear and turbid water (0 and ∼100 nephelometric turbidity units). Feeding assays were conducted with two prey items, mud crabs (Panopeus spp.) that rely heavily on chemoreception to detect predators, and brown shrimp (Farfantepenaus aztecus) that use both chemical and visual cues for predator detection. Because turbidity reduced pinfish foraging on both mud crabs and shrimp, the changes in predation rates are likely driven by turbidity attenuating fish foraging ability and not by affecting prey vulnerability to fish consumers. Blue crab foraging was unaffected by turbidity, and blue crabs were able to successfully consume nearly all mud crab and shrimp prey. Turbidity can influence predator–prey interactions by reducing the feeding efficiency of visual predators, providing a competitive advantage to chemosensory predators, and altering top-down control in food webs.
1. In aquatic systems, many species rely primarily on visual cues to choose optimal foraging sites, capture prey and avoid potential threats. Increases in the turbidity of water reduce visibility and impede animals in determining the precise location of both predators and food. How individuals balance foraging decisions with anti-predator behaviour in turbid environments is not well understood. 2. Here, we tested the effects of turbidity and predation risk on the foraging behaviour and feeding of invertivorous fish (Moenkhausia forestii (Characidae)) using a mesocosm experiment with a 2x2 design, crossing water clarity (clear vs. turbid) with predation risk (absence vs. presence of the piscivorous wolf-fish Hoplias aff. malabaricus (Erythrinidae)). We predicted that turbidity and predator presence interact additively to reduce foraging rate, and that increased turbidity or predator presence result in disproportionate food partitioning among shoal members. 3. The combination of high turbidity and predator presence resulted in a significant reduction in prey consumption. Foraging success exhibited a skewed distribution in the turbid treatment, i.e. there was a decreased evenness of food partitioning within shoals. Hence, both turbidity and predator presence affect the prey consumption and foraging behaviour of invertivorous fish, with turbidity amplifying the non-lethal effects of predation risk on foraging success. 4. Our results imply that turbidity-induced visual obstruction amplifies the negative effects of predator presence on invertivorous fish feeding behaviour, resulting in higher prey survival. Also, our finding that food intake by an intermediate consumer decreased in turbid water with a top predator lends no support to the hypothesis that intermediate consumer fish reduce their anti-predator behaviour in turbid water. 5. From a management perspective, our findings suggest that the oligotrophication of aquatic systems could (i) dramatically increase predation on basal prey organisms naturally adapted to turbid waters, and (ii) reduce within-shoal differences in feeding behaviour.
Effects of Turbidity and Acidity on Predator-Prey Interactions
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 J Environ Sci Public Health 2019; 3 [2]: 246-256 247 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.