The effect of prey mobility, prey contrast, turbidity and spectral composition on the reaction distance of Gobiusculus flavescens to its planktonic prey

The reaction distance of Gobiusculus flavescens to mobile and immobile copepod prey of different transparency was studied in water conditions with different turbidity levels or spectral composition. Both prey contrast (red or transparent Calanus spp.) and prey mobility caused reaction distance of G. flavescens to increase. The effect of prey mobility or prey transparency on reaction distance was independent of turbidity level. Longest reaction distances were measured for mobile and red prey at intermediate turbidity levels (10–20 JTU). Contrast threshold decreased with increasing turbidity. Although contrast of red and transparent copepod prey increased with increasing wavelength, longest reaction distances were observed at shorter wavelengths (blue–green). Lowest contrast threshold was found at shorter wavelengths. Visual pigments of G. flavescens are adapted to its natural environment. Both turbidity and spectral composition influenced G. flavescens contrast threshold.     

Effects of turbidity on the spontaneous and prey-searching activity of juvenile Atlantic cod (Gadus morhua)

Increasing turbidity in coastal waters in the North Atlantic and adjacent seas has raised concerns about impacts on Atlantic cod (Gadus morhua) using these areas as nurseries. A previous experiment (Meager et al. 2005 Can. J. Fish. Aquat. Sci. 62, 1978-1984) has shown that turbidity (up to 28 beam attenuation m-1) had little effect on the foraging rate of juvenile cod. Although this was attributed to cod using chemoreception in conjunction with vision to locate prey, foraging rates may also be maintained by increased activity. Higher activity, however, is energetically costly and may offset benefits from increased foraging return. We examined the effects of turbidity on prey searching and spontaneous activity of juvenile cod in the laboratory, by measuring activity with and without prey cues. Activity of juvenile cod was nonlinearly affected by turbidity and was lower at intermediate turbidity, regardless of the presence of prey odour. Activity increased over time when prey odour was present and decreased when absent, but the effects of prey odour were similar across all turbidity levels. Position in the tank was unaffected by turbidity or prey odour. Reduced activity at intermediate turbidities is likely to offset longer prey-search times. At high turbidity (greater than 17m-1), both longer prey-search times and higher activity indicate that increased energetic costs are probable.     

To fear or to feed: the effects of turbidity on perception of risk by a marine fish

Coral reefs are currently experiencing a number of worsening anthropogenic stressors, with nearshore reefs suffering from increasing sedimentation because of growing human populations and development in coastal regions. In habitats where vision and olfaction serve as the primary sources of information, reduced visual input from suspended sediment may lead to significant alterations in prey fish behaviour. Here, we test whether prey compensate for reduced visual information by increasing their antipredator responses to chemically mediated risk cues in turbid conditions. Experiments with the spiny damselfish, Acanthochromis polyacanthus, found that baseline activity levels were reduced by 23 per cent in high turbidity conditions relative to low turbidity conditions. Furthermore, risk cues elicited strong antipredator responses at all turbidity levels; the strongest antipredator responses were observed in high turbidity conditions, with fish reducing their foraging by almost 40 per cent, as compared with 17 per cent for fish in clear conditions. This provides unambiguous evidence of sensory compensation in a predation context for a tropical marine fish, and suggests that prey fish may be able to behaviourally offset some of the fitness reductions resulting from anthropogenic sedimentation of their habitats.     

Non-additive effects of macrophyte cover and turbidity on predator–prey interactions involving an invertivorous fish and different prey types

Habitat complexity, turbidity and prey type availability affect trophic dynamics, and an improved understanding of how these three factors work together could facilitate interpretations of trophic dynamics in environments with regime shifts. We conducted an experiment to cross these three factors, hypothesising that increasing both turbidity and macrophyte cover reduce consumption of Chironomids more than they reduce consumption of Cypridids. Our results did not support our hypothesis, suggesting that the effect of macrophyte cover on predation depends on turbidity. However, the magnitude of this combined effect is the same as that of turbidity alone. Moreover, turbidity affected predation on both prey types similarly. In addition, the effect of macrophyte cover on predation also depended on prey type. We argue that visual and physical refuges may be as effective as shelter, but macrophyte cover may benefit smaller prey items. This may lead to higher predation rates by small-sized fish on invertebrates during periods of low turbidity devoid of macrophyte cover and to similar predation rates on invertebrates during periods of low turbidity and abundant macrophytes, high turbidity and scarce macrophytes or high turbidity and abundant macrophyte cover.     

The effects of turbidity on prey consumption and selection of zooplanktivorous Gasterosteus aculeatus L.

It is well documented that reduced visibility caused by elevated turbidity can affect feeding of fish, yet the extent to which selective zooplanktivory is altered in turbid conditions remains ambiguous. In this study, we examined the influence of natural sediment-induced turbidity on the overall prey consumption and selective predation of a common brackish water littoral zooplanktivore, the particulate feeding three-spined stickleback (Gasterosteus aculeatus L.). We hypothesized that the effects of turbidity on prey consumption and prey type selection would be pronounced due to the vision-oriented feeding of this species and that these effects would differ between genders. Using aquarium experiments with three different groups of cladocerans and copepods varying in size and behavior, we studied prey consumption and selectivity of this key planktivore in varying turbidity treatments. Our results indicated significantly decreased total prey consumption in the high turbidity treatments, as well as altered selective feeding on copepods and an enhanced preference for larger cladocerans. We found gender-dependent differences in prey consumption, which are consistent with observations of other visually feeding fish with sexual size dimorphism. We conclude that high turbidity, such as that occurring in shallow coastal areas, may affect selective feeding in vision-oriented zooplanktivores and that these effects may be gender-related.     

The effects of turbidity and an invasive species on foraging success of rosyside dace (Clinostomus funduloides)

1.  Habitat degradation and biological invasions are important threats to fish diversity worldwide. We experimentally examined the effects of turbidity, velocity and intra- and interspecific competition on prey capture location, reactive distance and prey capture success of native rosyside dace ( Clinostomus funduloides ) and invasive yellowfin shiners ( Notropis lutipinnis ) in Coweeta Creek, North Carolina, U.S.A.
2.  Increased turbidity and velocity produced significant decreases in the number of prey captured forward of the fish's location. It is possible that this represents an increase in the amount of energy expended per prey captured.
3.  We used Akaike's Information Criterion (AIC) to evaluate competing explanatory models for reactive distance (10 generalised linear models, GLM) and prey capture success (9 generalised linear mixed models, GLMM).
4.  Reactive distance decreased by 12% with an increase from 2 to 4 conspecifics, whereas a 10 NTU increase in turbidity reduced reactive distance by 9%. Capture success was affected by velocity, dominance and competition, and varied among species. A 6 cm s⁻¹ increase in velocity produced a 28% decline in capture probability; however, dominant fish were 3.2 times more likely to capture a prey item than non-dominant fish. Yellowfin shiners only were 0.62 times as likely to capture a prey item as rosyside dace. Both intra- and interspecific competition reduced capture probability, and fish in high density intraspecific or interspecific trials were 0.46 times and 0.44 times as likely to capture prey, respectively, as fish in two fish intraspecific trials.
5.  These results suggest behavioural variables are as important as physical factors in determining reactive distance and capture probability by these minnows.     

The effect of turbidity and illumination on the reaction distance and search time of the marine planktivore Gobiusculus flavescens

Both reduced illumination and increased turbidity caused a significant reduction in reaction distance of Gobiusculus flavescens . The longest reaction distance, 18.9 cm for larger prey (Calanus finmarchicus) , occurred at a light level of 80 μmol m ⁻² s ⁻¹ compared to 12.9 cm for a smaller prey (Acartia clausi) at 8 μmol m⁻² s⁻¹. Above a light saturation level of 10 μmol m⁻² s⁻¹, additional light had little influence on reaction distance. In the turbidity experiments, the longest reaction distances were measured at turbidity levels of 10–20 JTU. Prey size influenced reaction distance at all tested light levels. Search time was influenced by prey size only at low illumination. With increasing turbidity, reaction distance to a group of prey was longer than to one prey.     

Visual feeding of fish in a turbid environment: Physical and behavioural aspects

Turbidity has both positive and negative effects on prey detection, by increasing or diminishing the contrast between prey and background due to the scattering of light. The positive effect of turbidity on prey contrast depends on the optical properties, scattering properties of suspended particles and the visual sensitivity of the predator.

The positive effect of turbidity is pronounced for larval fish, given that their visual field is short, leaving fewer particles between them and their prey to scatter light and interfere with detection. This relationship, together with a decreased risk of predation, makes turbid environments more optimal for some species and size groups of fish (planktivores and fish larvae) and less so for others (adult piscivore fish). Thus, turbidity might have a structuring effect on a fish community. Recently it has been demonstrated that UV light might have positive effects on prey detection and consumption. How UV light might interact with different kinds of particles producing turbidity is not well documented.     

Effects of turbidity and prey density on the foraging success of age 0 year yellow perch Perca flavescens

Laboratory experiments were conducted to determine how larval and juvenile yellow perch Perca flavescens respond to changes in prey density when exposed to different levels and types of turbidity (phytoplanktonic or sedimentary). Across prey densities, consumption by P. flavescens tended to be less in phytoplanktonic turbidity compared with sedimentary turbidity. For larvae, this effect was dependent on turbidity level (consumption differed between turbidity types only at high turbidity), while for juveniles the difference with turbidity type was equal across turbidity levels. These results suggest that phytoplankton blooms are detrimental to the ability of late season age 0 year P. flavescens to forage and support the need to control factors leading to excessive phytoplankton growth in lakes.     

Visual Detection of Speckles in the Fish Xenotoca variata by the Predatory Snake Thamnophis melanogaster in Water of Different Turbidity

Semi-aquatic snakes integrate visual and chemical stimuli, and prey detection and capture success are therefore linked to the display of visual predatory behavior. The snake Thamnophis melanogaster responds preferentially to individuals of the fish Xenotoca variata with a greater number of bright, colorful spots (lateral speckles) compared with those with a smaller number; however, water turbidity can reduce underwater visibility and effect the vulnerability of fish. In this study, we tested whether the presence of iridescent speckles on the flanks of male X. variata interacted with water turbidity to modify the predatory behavior displayed by the snake T. melanogaster. We predicted that in an experimental laboratory test, the snakes would increase the frequency of their predatory behavior to the extent that the water turbidity decreases. The snakes were tested at six different levels of water turbidity, in combination with three categories of male fish (with few, a median number of, or many speckles). The results showed that in a pool with high or zero turbidity, the number of speckles is not a determining factor in the deployment of the predatory behavior of the snake T. melanogaster toward X. variata. Our findings suggest that snakes can view the fish at intermediate percentages of turbidity, but the number of speckles in male X. variata is irrelevant as an interspecific visual signal in environments with insufficient luminosity. The successful capture of aquatic prey is influenced by integration between chemical and visual signals, according to environmental factors that may influence the recognition of individual traits.     

Visual feeding of fish in a turbid environment: Physical and behavioural aspects

Turbidity has both positive and negative effects on prey detection, by increasing or diminishing the contrast between prey and background due to the scattering of light. The positive effect of turbidity on prey contrast depends on the optical properties, scattering properties of suspended particles and the visual sensitivity of the predator. The positive effect of turbidity is pronounced for larval fish, given that their visual field is short, leaving fewer particles between them and their prey to scatter light and interfere with detection. This relationship, together with a decreased risk of predation, makes turbid environments more optimal for some species and size groups of fish (planktivores and fish larvae) and less so for others (adult piscivore fish). Thus, turbidity might have a structuring effect on a fish community. Recently it has been demonstrated that UV light might have positive effects on prey detection and consumption. How UV light might interact with different kinds of particles producing turbidity is not well documented.     

Interplay of individual interactions and turbidity affects the functional response of three-spined sticklebacks Gasterosteus aculeatus

The effects of turbidity, size and the presence of conspecifics on the functional response, feeding latency and activity in the three-spined stickleback Gasterosteus aculeatus were examined. A significant interaction between standard length and presence of conspecifics demonstrated an increase in attack rates of larger individuals in the presence of conspecifics. Attack rate was also higher in turbid water. Feeding latency decreased with prey concentration and presence of conspecifics, but was not affected by turbidity. Activity level did not change with prey levels, but increased with turbidity. These results can help to better understand how individual flexibility in the functional response can affect prey mortality according to environmental perturbation and social interaction at the level of the predator.     

Reduction of Reactive Distance and Foraging Success in Smallmouth Bass, Micropterus dolomieu, Exposed to Elevated Turbidity Levels

We determined how turbidity affected the reactive distance and foraging success of smallmouth bass, Micropterus dolomieu. Smallmouth bass reactive distance decreased exponentially with increasing turbidity, from 65cm in clear water to 10cm at the highest turbidity. Turbidity significantly decreased the probability of a fish reacting to a prey item, but did not influence foraging success following reaction to the prey. Elevated turbidity may reduce stream fish foraging efficiency and decrease prey consumption.     

Influence of chemical and visual stimuli in food-search behaviour of Procambarus clarkii under clear conditions

Chemical communication may play a major role in aquatic environments because of visibility limitations, but when turbidity is reduced do chemical and visual stimuli interact to elicit food-search behaviour by Procambarus clarkii? Does P. clarkii use visual cues to detect its prey? We conducted behavioural experiments in a Y maze, under non-turbid conditions. In the experiments P. clarkii was exposed to chemical plus visual (CV) and visual only (V) stimuli transmitted by Chironomus riparius. The results revealed that P. clarkii detected CV and V cues associated with the presence of C. riparius. In controls, with no prey, crayfish displayed only searching behaviour, whereas in treatments they exhibited searching, detection and attack behaviours. Further, there were no significant differences between CV and V stimuli in the mean number of attacks performed by crayfish. Thus, our findings indicate that under low turbidity, visual cues are sufficient to mediate prey detection by P. clarkii.     

Suspended sediment alters predator–prey interactions between two coral reef fishes

Sediment derived from agriculture and development increases water turbidity and threatens the health of inshore coral reefs. In this study, we examined whether suspended sediment could change predation patterns through a reduction in visual cues. We measured survivorship of newly settled Chromis atripectoralis exposed to Pseudochromis fuscus, a common predator of juvenile damselfishes, in aquaria with one of four turbidity levels. Increased turbidity led to a nonlinear response in predation patterns. Predator-induced mortality was ~50 % in the control and low turbidity level, but exhibited a substantial increase in the medium level. In the highest turbidity level, predation rates declined to the level seen in the control. These results suggest an imbalance in how the predator and prey cope with turbidity. A turbidity-induced change to the outcome of predator–prey interactions represents a major change to the fundamental processes that regulate fish assemblages.     

Thorn fish Terapon jarbua (Forskål) predation on juvenile white shrimp Penaeus indicus H. Milne Edwards and brown shrimp Metapenaeus monoceros (Fabricius): the effect of turbidity, prey density, substrate type and pneumatophore density

A series of laboratory experiments was conducted at Inhaca Island Marine Biological Station, Mozambique, in order to assess the separate effects of turbidity, prey density, substrate type, pneumatophore density, and the combined effects of turbidity with the latter three, on rate of predation by the thorn fish Terapon jarbua (Forskål, 1775) on white shrimp Penaeus indicus and brown shrimp Metapenaeus monoceros.Significant interactions between turbidity and the other three factors on shrimp predation for both prey species were detected. Regardless of prey density, increasing turbidity decreased predation on P. indicus, but not on M. monoceros, for which increasing densities reduced the protective effect of turbidity. Increasing prey density increased predation on P. indicus in clear water, and increased predation on M. monoceros in low and high, but not in intermediate turbidity or clear water. The presence of a substrate suitable for burying decreased predation on M. monoceros in clear water, but not in the turbidity levels used. In clear water, solely sandy-shell substrate afforded protection to P. indicus, while in turbid water, no substrate offered significant protection and muddy substrate even increased prey vulnerability to fish probably as a result of increased preys' locomotor activity. Raising pneumatophores density seems to lower the protective value of turbidity for both species. In clear water, only low and high structure density provided a deterrent effect on predation on P. indicus; in turbid water, intermediate and higher structure density increased predation. Increasing structural complexity reduced predation on M. monoceros linearly in clear water; but in low turbid water it increased. In high turbid waters, the increase was only significant in intermediate pneumatophore density. High structural complexities impair the pursuing capacity of fish and thus decreased predation rates. The results indicate that the effective provision of shelter of different habitats depends not only on the various environmental parameters analysed, but also on the way they interact and on the behaviour of prey and predator as well.     

Effects of crayfish size,orientation, and movement on the reactive distance of largemouth bass foraging in clear and turbid water

Laboratory experiments were performed in clear and turbid water to determine the effects of prey size, orientation, and movement on the reactive distance of largemouth bass (Micropterus salmoides) when feeding on crayfish (Procambarus acutus). In clear water, the reactive distance increased linearly with an increase in prey size, and prey movement resulted in a significant increase in the reactive distance. Prey orientation (head-on versus perpendicular) did not change the reactive distances. In moderately turbid water, the reactive distance did not increase with increased prey size, and prey movement did not result in any changes in the reactive distance. The absence of any effects of prey orientation in clear water or prey movement in turbid water is inconsistent with results from studies using different species (primarily planktivorous fish). I propose that largemouth bass change their foraging tactics as prey visibility changes. When prey are highly visible (low turbidity), predators attack (react) only after prey recognition, which is based on multiple cues such as prey size (length, width) and movement. When prey are less visible (high turbidity), predators attack immediately upon initial prey sighting, which does not depend on prey size or movement.     

Turbidity amplifies the non‐lethal effects of predation and affects the foraging success of characid fish shoals

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Effect of prey type and inorganic turbidity on littoral predator–prey interactions in a shallow lake: an experimental approach

Predation often represents the prevailing process shaping aquatic ecosystems. As foraging and antipredatory behaviour frequently relate to vision, turbidity may often impair the interactions between the predator and its prey, depending on prey type and source and level of turbidity. We studied the effect of inorganic turbidity (0–30 NTU) on the effectiveness of fish feeding on two types of prey in different habitats: free-swimming cladoceran (Daphnia pulex) in open water and plant-associated cladoceran (Sida crystallina) attached to Nuphar lutea leaves. For the planktivore, we used vision-oriented perch (Perca fluviatilis) common in the littoral zone of temperate lakes. In our study, increasing inorganic turbidity did not appear to initiate any significant change in the feeding efficiency of perch on free-swimming Daphnia pulex. However, we saw a markedly different feeding efficiency when perch targeted plant-attached Sida crystallina. Our results substantiate that floating-leaved macrophytes in turbid lakes may provide a favourable habitat for plant-attached cladocerans.     

Growth of pike larvae: effects of prey, turbidity and food quality

We studied experimentally the effects of turbidity and prey composition on pike larval growth and hypothesized that pike larval growth varies with turbidity and food quality. We reared the first-feeding pike larvae (Esox lucius) in laboratory tanks with (1) clear or (2) turbid water provided with zooplankton rations from (3) an inner and (4) an outer archipelago site. The sites differ in physical features, salinity, eutrophication status, zooplankton community structure and density. Pike larvae showed the highest weight increase in clear water with zooplankton from the outer site and the poorest weight increase in turbid water with zooplankton as prey from the inner site. Our fatty acid analysis revealed that unsaturated fatty acid levels were highest in the outer site. The relative percentage of copepods was also higher in the outer site. This study supports the hypothesis that turbidity weakens the ability of pike larvae to capture certain prey. Further, zooplankton community composition matters in turbid water, but is not a primary factor in clear water.