Variation in plant stem density and its effects on foraging success of juvenile bluegill sunfish

Synopsis Juvenile bluegill sunfish, Lepomis macrochirus, are known to use beds of aquatic vegetation as a refuge from predators. This study examines the effects of increasing plant stem density on juvenile bluegill foraging. Three stem densities (100, 250 and 500 stems m⁻²), varying in their refuge potential for bluegills from predators, were tested. Results demonstrate that stem densities chosen as a refuge from predation (i.e. 500 stems m⁻²) significantly reduced bluegill foraging success and increased time required to capture prey. Therefore, juvenile bluegills seeking safety in vegetation may be faced with a trade-off between foraging success and effective refuge from predation when choosing among plant stem densities.     

Behavioural Response of Juvenile Bluegill Sunfish to Variation in Predation Risk and Food Level

The behavioural response of juvenile bluegill sunfish (Lepomis macrochirus) to predation risk when selecting between patches of artificial vegetation differing in food and stem density was investigated. Bluegill foraging activity was significantly affected by all three factors. Regardless of patch stem density or risk of predation bluegills preferred patches with the highest prey number. During each trial bluegill foraging activity was clearly divided into a between- and within-patch component. In the presence of a predator bluegills reduced their between-patch foraging activity by an equivalent amount regardless of patch stem density or food level, apparently showing a risk-adjusting behavioural response to predation risk. Within patches, however, foraging activity was affected by both food level and patch stem density. When foraging in a patch offering a refuge from predation, the presence of a predator had no effect on bluegill foraging activity within this patch. However, if foraging in a patch with only limited refuge potential, bluegill foraging activity was reduced significantly in the presence of a predator. Further, this reduction was significantly greater if the patch contained a low versus a high food level, indicating a risk-balancing response to predation with respect to within-patch foraging activity. Both these responses differ from the risk-avoidance response to predation demonstrated by juvenile bluegills when selecting among habitats. Therefore, our results demonstrate the flexibility of juvenile bluegill foraging behaviour.     

Predator foraging success and habitat complexity: quantitative test of the threshold hypothesis

Summary Numerous studies have demonstrated a negative relationship between increasing habitat complexity and predator foraging success. Results from many of these studies suggest a non-linear relationship, and it has been hypothesised that some threshold level of complexity is required before foraging success is reduced significantly. We examined this hypothesis using largemouth bass (Micropterus salmoides) foraging on juvenile bluegill sunfish (Lepomis macrochirus) in various densities of artificial vegetation. Largemouth foraging success differed significantly among the densities of vegetation tested. Regression analysis revealed a non-linear relationship between increasing plant stem density and predator foraging success. Logistic analysis demonstrated a significant fit of our data to a logistic model, from which was calculated the threshold level of plant stem desity necessary to reduce predator foraging success. Studies with various prey species have shown selection by prey for more complex habitats as a refuge from predation. In this stydy, we also examined the effects of increasing habitat complexity (i.e. plant stem density) on choice of habitat by juvenile bluegills while avoiding predation. Plant stem density significantly effected choice of habitat as a refuge. The relationship between increasing habitat complexity and prey choice of habitat was found to be positive and non-linear. As with predator foraging success, logistic analysis demonstrated a significant fit of our data to a logistic model. Using this model we calculated the threshold level of habitat complexity required before prey select a habitat as a refuge. This density of vegetation proved to be considerably higher than that necessary to significantly reduce predator foraging success, indicating that bluegill select habitats safe from predation.Implications of these results and various factors which may affect the relationships described are discussed.     

Plant stem density as a cue in patch choice by foraging juvenile bluegill sunfish

Synopsis Juvenile bluegill sunfish,Lepomis macrochira, are restricted to vegetated habitats by predators. Variation in plant stem density has a significant effect on bluegill foraging success. Given the mosaic nature of this habitat, plant stem density may provide a cue for selecting among patches in which to forage. In this study, juvenile bluegills were offered patches of artificial vegetation differing only in plant stem density as potential foraging sites. Three densities, 100, 250, and 500 stems m^–2 were tested. Fish were presented with a choice between patches (100:250, 250:500, or 100:500). Bluegill foraging rate in, and the number of fish choosing each patch was recorded. Juvenile bluegills showed a preference for those patches which maximized their foraging rate.     

Behavior of fish predators and their prey: habitat choice between open water and dense vegetation

Synopsis Behavior of largemouth bass, Micropterus salmoides, and northern pike, Esox lucius, foraging on fathead minnows, Pimephales promelas, or bluegills, Lepomis macrochirus, was quantified in pools with 50% cover (half the pool had artificial stems at a density of 1000 stems m⁻²). Both predators spent most of their time in the vegetation. Largemouth bass searched for bluegills and ambushed minnows, whereas the relatively immobile northern pike ambushed all prey. Minnows were closer to predators and were captured more frequently than bluegills. Even when minnows dispersed, they moved continually and eventually wandered within striking distance of a predator. Bluegills dispersed in the cover with predators. Bass captured the few bluegills that strayed into the open and pike captured those that approached too closely in the cover. The ability of predators to capture prey while residing in habitats containing patches of dense cover may explain their residence in areas often considered to be poor ones for foraging. The unit is sponsored jointly by the United States Fish and Wildlife Service, Ohio Department of NaturalResources, The Ohio State University, and the Wildlife Management Institute     

Predator-induced delayed maturity in bluegill sunfish (Lepomis macrochirus): variation among populations

Previous studies suggested that differences in age at maturity among populations of bluegill sunfish (Lepomis macrochirus) were not genetically based, but rather were a phenotypic response to the presence of predators. I conducted two experiments to determine if the presence of largemouth bass affected age at maturity in bluegill sunfish. Bluegills from three populations were tested to see if the response to the threat of predation varied among source populations. Juvenile bluegills were maintained in the presence of predators or in controls with no contact with predators. Refuge use and growth were monitored during the experiments and reproductive activity was evaluated when bluegills reached age 1. Bluegills from one population exhibited delayed maturity in the presence of predators. Individuals from the other two populations showed no significant differences between predator and control treatments. The population that responded to the presence of predators had a history of high predation levels over the past 30–40 years. The other populations had a history of low levels of predation. This study suggests that presence of predators can induce phenotypic shifts in age at maturity of bluegills, but that the magnitude of response varies among populations in a manner consistent with historical patterns of coexistence. Received: 7 August 1996 / Accepted: 8 August 1997     

Effects of turbidity and an invasive waterweed on predation by introduced largemouth bass

Anthropogenic activities lead to changes in characteristics of aquatic ecosystems, including alteration of turbidity and addition of invasive species. In this study, we tested how changes in turbidity and the recent invasion of an aquatic macrophyte, Egeria densa, may have changed the predation pressure by introduced largemouth bass on juvenile striped bass and delta smelt, two species that have seen a drastic decline in recent decades in the Sacramento-San Joaquin Delta. In a series of mesocosm experiments, we showed that increases in vegetation density decreased the predation success of largemouth bass. When placed in an environment with both open water and vegetated areas, and given a choice to forage on prey associated with either of these habitats, largemouth bass preyed mainly on open water species as opposed to vegetation-associated species, such as juvenile largemouth bass, bluegill or red swamp crayfish. Finally, we showed that turbidity served as cover to open water species and increased the survival of delta smelt, an endemic species at risk. We also found that such open water prey tend not to seek refuge in the vegetation cover, even in the presence of an imminent predation threat. These results provide the beginning of a mechanistic framework to explain how decreases in turbidity and increases in vegetation cover correlate with a decline of open water species in the Sacramento-San Joaquin Delta.     

Phenotypic variation and associated predation risk of juvenile common carp Cyprinus carpio

Juvenile common carp Cyprinus carpio were collected from 10 lakes with variable predator abundance over 4 months to evaluate if morphological defences increased with increasing predation risk. Cyprinus carpio dorsal and pectoral spines were longer and body depth was deeper when predators were more abundant, with differences becoming more pronounced from July to October. To determine if morphological plasticity successfully reduced predation risk, prey selection of largemouth bass Micropterus salmoides foraging on deep- and shallow-bodied C. carpio was evaluated in open and vegetated environments. Predators typically selected deep- over shallow-bodied phenotypes in open habitats and neutrally selected both phenotypes in vegetated habitats. When exposed to predators, shallow-bodied C. carpio phenotypes shoaled in open habitat, whereas deep-bodied phenotypes occupied vegetation. Although deep-bodied phenotypes required additional handling time, shallow-bodied phenotypes were more difficult to capture. These results suggest that juvenile C. carpio gradually develop deeper bodies and larger spines as predation risk increases. Morphological defences made it more difficult for predators to consume these prey but resulted in higher vulnerability to predation in some instances.     

Performance as a fish predator of largemouth bass [<Emphasis Type="Italic">Micropterus salmoides</Emphasis> (Lacepède)] invading Japanese freshwaters: a review

This review focuses on how predator performance of the invasive largemouth bass [Micropterus salmoides (Lacepède)] has been, or will be, formed in Japanese freshwaters. Predation impacts of largemouth bass on fish communities appear pervasive in both Japanese as well as North American freshwaters. Factors affecting performance as a piscivorous predator are (1) light intensity and water clarity, (2) oxygen depletion, (3) prey size and gape size, (4) behavioral refuge of prey, (5) weed beds as refuge for prey fish, (6) interaction with bluegill. Size and behavioral refuges requirements are so rigorous that they may have evolved only in some North American prey fish species like bluegill; therefore, most Japanese native fish species are unlikely to be equipped with such refuges. However, refuge habitats like aquatic weed beds could develop in Japanese freshwaters, allowing prey fish species to survive under predation pressure. The density, architecture, and species composition of aquatic plants may affect their suitability as refuges. Studies in Japanese waters have suggested that the presence of rich aquatic vegetation or invasive bluegill in bass-introduced waters have suppressed the predation impact of largemouth bass on fish communities. In addition to these environmental factors, original genotypic and phenotypic traits of the introduced largemouth bass, and hybridization between different lineages of largemouth bass or with Florida bass [Micropterus floridanus (Lesueur)] may be involved in further adaptation of invasive largemouth bass to Japanese freshwaters.     

Habitat requirements of weasels <Emphasis Type="Italic">Mustela nivalis</Emphasis> constrain their impact on prey populations in complex ecosystems of the temperate zone

Differences in habitat use by prey and predator may lead to a shift of occupied niches and affect dynamics of their populations. The weasel Mustela nivalis specializes in hunting rodents, therefore habitat preferences of this predator may have important consequences for the population dynamics of its prey. We investigated habitat selection by weasels in the Bia?owie?a Forest in different seasons at the landscape and local scales, and evaluated possible consequences for the population dynamics of their prey. At the landscape scale, weasels preferred open habitats (both dry and wet) and avoided forest. In open areas they selected habitats with higher prey abundance, except during the low-density phase of the vole cycle, when the distribution of these predators was more uniform. Also in winter, the distribution of weasels at the landscape scale was proportional to available resources. In summer, within open dry and wet habitats, weasels preferred areas characterised by dense vegetation, but avoided poor plant cover. In winter, weasels used wet open areas proportionally to availability of habitats when hunting, but in contrast to summer, they rested only in habitats characterized by a lower water level, which offered better thermal conditions. At the local scale, the abundance of voles was a less important factor affecting the distribution of these predators. Although we were not able to provide direct evidence for the existence of refuges for voles, our results show that they may be located within habitat patches, where availability of dense plant cover and physiological constraints limit the activity of weasels. Our results indicate that in complex ecosystems of the temperate zone, characterized by a mosaic pattern of vegetation types and habitat specific dynamics of rodents, impact of weasels on prey populations might be limited.     

Antipredator Behavior of American Bullfrogs (Lithobates catesbeianus) in a Novel Environment

Invasive species capable of recognizing potential predators may have increased establishment rates in novel environments. Individuals may retain historical predator recognition and invoke innate responses in the presence of taxonomically or ecologically similar predators, generalize antipredator responses, or learn to avoid risky species in novel environments. Invasive amphibians in aquatic environments often use chemical cues to assess predation risk and learn to avoid novel predators via direct experience and/or associated chemical cues. Ontogeny may also influence recognition; experience with predators may need to occur at certain developmental stages for individuals to respond correctly. We tested predator recognition in invasive American bullfrog ( Lithobates catesbeianus) tadpoles that varied in experience with fish predators at the population and individual scale. We found that bullfrog tadpoles responded to a historical predator, largemouth bass ( Micropterus salmoides), only if the population was locally sympatric with largemouth bass. Individuals from a population that did not co‐occur with largemouth bass did not increase refuge use in response to either largemouth bass chemical cues alone or chemical cues with diet cues (largemouth bass fed bullfrog tadpoles). To test whether this behavioral response was generalized across fish predators, we exposed tadpoles to rainbow trout ( Oncorhynchus mykiss) and found that tadpoles could not recognize this novel predator regardless of co‐occurrence with other fish species. These results suggest that environment may be more important for predator recognition than evolutionary history for this invasive species, and individuals do not retain predator recognition or generalize across fish predators.     

Invasive carp and prey community composition disrupt trophic cascades in eutrophic ponds

The role of trophic cascades in structuring freshwater communities has been extensively studied. Most of this work, however, has been conducted in oligotrophic northern lakes that contain highly vulnerable cyprinid prey: aquatic communities where trophic interactions are likely to be stronger than in many other systems. Fewer studies have been conducted in eutrophic systems or have examined the bottom-up effects of benthivorous fishes, and none have directly compared these effects to those of piscivores on ecosystem structure and function. We conducted enclosure experiments in eutrophic ponds to examine trophic effects of invasive benthivores (common carp—Cyprinus carpio L.), native piscivores (largemouth bass—Micropterus salmoides [Lacepède]), and their interactions with common centrarchid prey with well-developed anti-predatory behaviors (age-1 bluegill—Lepomis macrochirus Rafinesque and young-of-year largemouth bass). At the end of the 60-day experiment, common carp had strong bottom-up effects that increased total phosphorus and turbidity while decreasing chlorophyll a biomass and macrophyte cover that resulted in decreased macroinvertebrate biomass and also decreased growth in both juvenile largemouth bass and bluegill. Piscivorous largemouth bass, however, did not affect the survival of either planktivorous juvenile largemouth bass or bluegill. Growth of juvenile largemouth bass was also not affected, but juvenile bluegill growth was significantly diminished, possibly due to nonconsumptive effects of predation. Our results suggest that, in a centrarchid-dominated eutrophic system, top-down effects of predators are overwhelmed by common carp-mediated bottom-up effects. These bottom-up effects strongly affected multiple trophic levels, thus altering aquatic community structure and function.     

Grazer identity changes the spatial distribution of cascading trophic effects in stream pools

Non-lethal effects of predators on prey behavior can mediate trophic cascades, but the extent of effects depends on habitat characteristics and risk sensitivity of prey. Furthermore, predation risk for stream organisms varies along the depth gradient and strongly influences their behavior. Grazing minnows (Campostoma anomalum) and crayfish (Orconectes virilis) are both prey for largemouth bass (Micropterus salmoides) in streams, but differ in their predator-avoidance behavior. This study contrasts the effects and mechanisms of non-lethal trophic cascades on the spatial distribution of filamentous green algae among stream pools and along a depth gradient within pools. Presence/absence of a largemouth bass was crossed with four combinations of the two grazer species (0 grazers, 30 minnows, 30 crayfish, and 15 each) in outdoor, experimental streams. Grazer densities were maintained by restocking. I used geostatistics to quantify spatial patterns of predator and grazer habitat use, height of filamentous algae in the water column, and spatial covariation of water depth with algal height, and depth with grazer habitat use. In streams with only minnows, bass were sedentary, and hid within tall algae in a single "bass pool". In pools with grazed algae, bass actively pursued prey within and among pools and used deeper water. This set up a hierarchy of risk to grazers along the depth gradient from bass in deep water to potential risk from terrestrial predators in shallow water. Thus, minnows were more sensitive than crayfish to predation risk from bass, but less sensitive than crayfish to risk from terrestrial predators. Minnows mediated cascades at the scale of whole pools by avoiding "bass pools", but only if crayfish were absent. Crayfish avoided potential interactions both with terrestrial predators and bass by grazing and burrowing in deeper water at night (when bass were inactive), and by hiding in burrows during daytime. Crayfish without burrows avoided bass and crayfish defending burrows by using shallow edges of pools as corridors, but did not graze there. Thus, crayfish-mediated cascades were limited to pool edges. Effects of grazer identity may extend to other consumers via modification of risk for biota that use filamentous algae as either foraging or refuge habitat.     

How light, a predator, and experience influence bluegill use of shade and schooling

Bluegills, Lepomis macrochirus, form schools and use shade to avoid predators. How light intensity, predators, and experience might affect antipredator behavior of bluegill are not well understood. Hence, we evaluated use of shade and schooling by naive (hatchery) and experienced (wild) bluegills (50–60 mm total length) at four light levels (1.5, 85, 169, 340 lux) in the presence and absence of a model predator in experimental pools. Naive bluegills used shade extensively at all light levels, even when the predator was in the shade. They rarely schooled, preferring to shoal in the shade. Experienced bluegill used shade when the predator was in the open and avoided shade when the predator was there. Schooling was more prevalent at low light levels when shade was less intense. Use of shade became an increasingly important behavior at higher light levels, unless the predator was in the shade. A shaded predator caused experienced bluegills to shoal tightly in the opposite, open area. These data suggest naive bluegills may not have considered the model predator a threat. Their behavior suggests avian predator avoidance, a possibility given that avian predators were present at the hatchery. Experienced bluegill employed behaviors that would be useful in avoiding piscine predators.     

Body size and substrate association of littoral insects in relation to vegetation structure

Variation in substrate association types and maximum size of aquatic insects were studied in a vegetated littoral zone of three lake basins. The basins differed from each other in trophic status, biomass of benthivorous fish, and abundance of macrophytes. Four types of substrate association – swimmers, crawlers, semisessiles and burrowers, respectively – were assumed to represent decreasing vulnerability to fish predators. Large-sized species were also hypothesised to be more vulnerable to fish predators. The distributions of species traits were examined in relation to vegetation density. Inferring from ``predation hypothesis' opposite selection pressures on the species traits were expected along the vegetation density. Dense macrophyte beds were thought to be dominated by invertebrate predators and open water by fish predators, since the predation efficiency of fish decreases in complex environments. In the case of invertebrate predator domination, large size and higher activity should be favoured traits among the prey species. Distribution patterns of modes of the two studied traits were explored separately for predatory and non-predatory insects. As expected, swimmers and large-sized crawlers were characteristic of the insect assemblages of dense macrophyte beds. The densities of Odonata, Corixidae, Dytiscidae, Ephemeroptera and Sialidae were higher among macrophytes than in open water, where these insect taxa were possibly depleted by fish. On the other hand, the small-sized and fairly immobile Chironomidae were the most abundant group in open water. These results support the existence of a predator transition zone among littoral vegetation, ranging from domination of invertebrate predation among the dense beds to that of fish predation in open water.     

Variations in piscivory of invasive largemouth bass <Emphasis Type="Italic">Micropterus salmoides</Emphasis> associated with pond environments

Introductions of non-native predatory fishes can be a major driver of aquatic biodiversity loss. The largemouth bass Micropterus salmoides (L.) has been introduced throughout much of the world, thereafter negatively affecting native faunal communities owing to its predatory impact. To investigate the environmental factors affecting the predatory performance of invasive bass, we examined the stomach contents and habitat characteristics of bass in 15 irrigation farm ponds in northeastern Japan. The food habits of the bass populations differed among the studied ponds: the predominant prey items were fishes among bass in seven of the ponds, whereas aquatic invertebrates (mainly insects and zooplankton) were the predominant taxa in the diets of bass in the eight remaining ponds, with the onset of piscivory related to body size. The results of multivariate analysis indicated that the extent to which the bass consumed fish was positively associated with fish prey abundance and negatively associated with percentage of aquatic vegetation coverage. We suggest that the extent of aquatic vegetation coverage strongly influenced the predation efficiency of bass in the ponds. These findings might be employed to assess a pond ecosystem’s vulnerability to invasive largemouth bass and to reduce the predator’s impact on native fish species by improvements to the habitat.     

Influence of intra‐ and interspecific variation in predator–prey body size ratios on trophic interaction strengths

1. Predation is a pervasive force that structures food webs and directly influences ecosystem functioning. The relative body sizes of predators and prey may be an important determinant of interaction strengths. However, studies quantifying the combined influence of intra‐ and interspecific variation in predator–prey body size ratios are lacking.
2. We use a comparative functional response approach to examine interaction strengths between three size classes of invasive bluegill and largemouth bass toward three scaled size classes of their tilapia prey. We then quantify the influence of intra‐ and interspecific predator–prey body mass ratios on the scaling of attack rates and handling times.
3. Type II functional responses were displayed by both predators across all predator and prey size classes. Largemouth bass consumed more than bluegill at small and intermediate predator size classes, while large predators of both species were more similar. Small prey were most vulnerable overall; however, differential attack rates among prey were emergent across predator sizes. For both bluegill and largemouth bass, small predators exhibited higher attack rates toward small and intermediate prey sizes, while larger predators exhibited greater attack rates toward large prey. Conversely, handling times increased with prey size, with small bluegill exhibiting particularly low feeding rates toward medium–large prey types. Attack rates for both predators peaked unimodally at intermediate predator–prey body mass ratios, while handling times generally shortened across increasing body mass ratios.
4. We thus demonstrate effects of body size ratios on predator–prey interaction strengths between key fish species, with attack rates and handling times dependent on the relative sizes of predator–prey participants.
5. Considerations for intra‐ and interspecific body size ratio effects are critical for predicting the strengths of interactions within ecosystems and may drive differential ecological impacts among invasive species as size ratios shift.

     

Implications of a fluctuating fish predator guild on behavior, distribution, and abundance of a shared prey species: the grass shrimp Palaemonetes pugio

In some systems, the identity of a prey species' dominant predator(s) may not be constant over time. In cases in which a prey species exhibits different responses to various predator species, such changes in predator identity may have population-wide consequences. Our goals were to determine (1) whether mortality of and refuge use by the grass shrimp, Palaemonetes pugio, were predator-specific, and (2) how effects of prey size and habitat interacted with predator type. Striped bass (Morone saxatilis) exerted twice as much predation pressure as mummichog (Fundulus heteroclitus), although not equally as great on large (female) and small (male) shrimp. Mummichog, which fed preferentially on large shrimp, forced a partitioning of habitat between the two shrimp size classes. In contrast, large and small shrimp occupied similar habitats when subjected to striped bass, which fed on both size classes equally. Refuge use of grass shrimp depended on predator type. In the presence of mummichog, which occupied shallower depths in the water column than striped bass, shrimp stayed deep and close to structural habitat. Striped bass, which were deeper, caused shrimp to move high in the water column away from structural habitat. When both predators were present, shrimp distribution was similar to that when only striped bass were present, striped bass predation rate was enhanced, and overall mortality was higher than with either predator alone. Results suggest that at times when mummichogs are the dominant predators, large (female) shrimp experience higher predation than small (male) shrimp and are physically separated from their potential mates. When striped bass are more abundant, male and female shrimp may share a similar, shallow, less structure-oriented distribution and be subjected to higher mortality. When both predators are present, mortality rates may be higher still. This predator-, size-, and habitat-specificity of grass shrimp behavior suggests significant population and distribution consequences of fluctuating predator guilds and fluctuating cover of structural habitats in the field.     

Foraging and predator avoidance: a test of a patch choice model with juvenile bluegill sunfish

Summary In situations where foraging sites vary both in food reward and predation risk, conventional optimal foraging models based on the criterion of maximizing net rate of energy intake commonly fail to predict patch choice by foragers. Recently, an alternative model based on the simple rule when foraging, minimize the ratio of mortality rate (u) to foraging rate (f) was successful in predicting patch preference under such conditions (Gilliam and Fraser 1987). In the present study, I compare the predictive ability of these two models under conditions where available patches vary both in predation hazard and foraging returns. Juvenile bluegill sunfish (Lepomis macrochirus) were presented with a choice between two patches of artificial vegetation differing in stem density (i.e. 100, 250, and 500 stems/m²) in which to forage. Each combination (100:250, 250:500, or 100:500) was presented in the absence, presence, and after exposure to a bass predator (Micropterus salmoides). Which patch of vegetation bluegills chose to forage in, and foraging rate within each patch were recorded. Independent measurements of bluegill foraging rate and risk of mortality in the three stem densities provided the data for predicting patch choice by the two models. With no predator, preference between plots was consistent with the maximize energy intake per unit time rule of conventional optimality models. However, with a predator present, patch preference switched to match a minimize u/f criterion. Finally, when tested shortly after exposure to a predator (i.e. 15 min), bluegill preference appeared to be in a transitional phase between these two rules. Results are discussed with respect to factors determining the distribution of organisms within beds of aquatic vegetation.     

Fish predation on epiphytic microcrustacea in Tivoli South Bay,a Hudson River tidal freshwater wetland

The littoral microcrustacean fauna of Tivoli South Bay was studied from July to September, 1989. The effects of fish predation on microcrustacean densities were tested in a short-term predator exclusion experiment. Fish were excluded from water chestnut (Trapa natans) plots in four screened exclosures. An equal number of open cages allowed foraging. Fish predation did not have a significant effect on densities of ostracods or other microcrustaceans. Ostracod densities increased in cages throughout the experimental period, whereas cladoceran and copepod densities decreased in both treatments. Gut contents analysis of banded killifish (Fundulus diaphanus) revealed that ostracods and other microcrustaceans were commonly ingested by larval, juvenile, and adult killifish utilizing T. natans as habitat. These results suggest that ostracods and other microcrustacean epifauna associated with T. natans may represent an important trophic link in the tidal freshwater wetlands of the Hudson River Estuary. Deceased