Invasion of Laguncula pulchella (Gastropoda: Naticidae) and predator–prey interactions with bivalves on the Tona coast, Miyagi prefecture, northern Japan

On the Tona coast, Miyagi prefecture, northern Japan, interactions between the alien predator Laguncula pulchella and its bivalve prey were explored using annually collected quadrat samples over a 10 year period, from 2001 to 2010. A single L. pulchella individual was first recorded in 2002, and the density increased 12-fold from 2002 to 2004. In contrast, population densities of Ruditapes philippinarum and Macoma incongrua rapidly decreased during this interval. Based on frequency of predatory drill holes on the dead shells, more than 35 % of Ruditapes philippinarum and 20 % of Macoma incongrua died because of naticid predation after 2004, while Pillucina pisidium was less vulnerable to naticid predation. L. pulchella focused attacks on P. pisidium in 2004, when R. philippinarum and M. incongrua had became scarce due to naticid predation. This species-selective predation affected bivalve community structure, and caused disagreements in taxonomic composition and species’ rank-order abundance between the living bivalve community and the assemblage of dead shells. This approach (live–dead analysis), frequently used in paleoecological research, is a conservative tool to identify impacts of an alien predator on community structure. When sample size is sufficient, frequency of predatory drill holes in preferred prey species is likely to reflect predation intensity.     

Can Naticid Gastropod Predators Be Identified by the Holes They Drill?

We tested the hypothesis that drillholes made by different species of predatory naticid gastropods can be differentiated by variability in the inner (IBD) and outer borehole diameters (OBD) of the holes they drill. We compared two samples of Mya arenaria that were drilled by different predators, Euspira heros and Neverita duplicata, under experimental conditions. Mean IBD:OBD ratio was significantly greater for holes drilled by Euspira compared to Neverita, indicating that Euspira drills a steeper drillhole than Neverita. We also found consistent differences between the two naticids for slopes of regression lines of IBD on OBD after standardization for predator size and prey size and thickness, with slopes for Euspira being steeper, but results were not statistically significant. However, the range of IBD:OBD ratios was wide and overlapped considerably for each species, which decreases confidence in assignment of individual drillholes to a particular predator species. At least in the case of these two naticid species, interspecific differences in variation of the inner and outer diameters of the holes they drill have limited utility in identifying the maker of individual boring traces in the fossil record.     

Lethal and non-lethal effects of an invasive naticid gastropod on the production of a native clam

Predators often affect prey production not only by lethal predation but also by unintentional inhibition of feeding and growth. The present study examined the lethal and non-lethal effects of the invasive naticid Laguncula pulchella on the survival and growth of the prey clam Ruditapes philippinarum in a sandy tidal flat. Cages accommodating 30 clams (10 individuals × 3 size classes of ≤ 20 mm, 20–30 mm, and > 30 mm shell length) and one L. pulchella (approximately 37 mm shell height) per cage were buried in the tidal flat for 10 weeks. Medium sized clams were consumed by predators much more (80.5%) than small (12.2%) and large clams (7.3%). Clams were consumed by L. pulchella at a frequency of 0–2.5 individuals per predator per week. The growth of clams caged with L. pulchella was lower (23, 27, 33, 41, and 57% for clam of 10, 20, 30, 40, and 50 mm, respectively) than that in control cages (clams without L. pulchella). The clam burial depths did not increase by the presence of predators in a laboratory experiment, indicating that growth suppression was caused by the reduced feeding activity following physical disturbance and/or chemical signals. The results of this study demonstrate that the introduction of L. pulchella reduced the productivity of the commercially important clams not only by lethal predation but also by mere presence.     

Byssus production ability and degree of byssal-gland development in the infaunal clam Ruditapes philippinarum

Byssus production of Ruditapes philippinarum clams becomes reduced with growth. This tendency is well recognized but has not been analysed in detail. Additionally, it remains uninvestigated whether the lack of competence to produce byssus threads in the adult stage is caused by atrophy of the byssal glands or not. The objective of this study was to evaluate the byssus production ability of clams through the juvenile to adult stages and to examine the importance of two endogenous factors (i.e. shell size, somatic condition) in determining the byssus production probability (proportion of clams with byssus production in a population). This study also histologically confirmed the presence of byssal glands in juvenile to adult clams. For these purposes, field surveys to investigate the relationship among byssus production, shell size and somatic condition of clams collected from four intertidal sites and a histological study for byssal glands of the clams was conducted. This study revealed that byssus production probability decreases with increasing shell size and declining somatic condition and that the lack of byssus production is not caused by the loss of the byssal glands.     

A comparative study of samples of the bivalve <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis> (Adams et Reeve, 1850) from populations and shell assemblages

According to the results of a comparative analysis of the size and age structures of samples from a population of the bivalve mollusk Ruditapes philippinarum (Manila clam) and from shell assemblages of this species, the possibility of data acquisition on populations using samples from shell assemblages was assessed. A considerable coincidence of these parameters after taking the losses of small individuals during formation of shell assemblage into account, which depended on the location and conditions of assemblage formation, was recorded. Due to the good level of preservation of the shells of older individuals, the sample from the assemblage gave a more comprehensive appreciation of the maximum size and life span of the species than the sample of live mollusks from the natural habitat. Samples from shell assemblages may be used for growth rate estimation of clams without catching live individuals, as the results from studying the linear growth of mollusks based on samples from live populations and from shell assemblages did not differ significantly. Samples from many-year shell accumulations can also be useful for revealing the periods of the highest death rates, the most vulnerable periods in the ontogenesis of the mollusks, and, in some cases, the causes of their death.     

Comparing predatory drillholes to taphonomic damage from simulated wave action on a modern gastropod

Marine drilling predation, in which the predator bores a hole through shelled invertebrate prey, plays a role in the structure of benthic communities. As drilling often leaves the prey shell otherwise undamaged, the resulting holes are also an excellent proxy for drilling predation pressure in the fossil record. Considering that a large number of predation studies focus on drilling predation in the fossil record, it is crucial that we are able to distinguish true drilling predation from taphonomy. The purpose of this study is to determine damage on Olivella biplicata shells, drilled by naticid gastropods, is distinguishable from taphonomically produced damage to these shells. In addition, the potential for preferential breakage due to either the presence or whether absence of a drillhole was investigated. Drilled and non-drilled O. biplicata shells were tumbled to simulate wave action and were checked at intervals to record accumulated damage. Drilled and non-drilled shells do not show a significant difference in damage accumulated while undergoing simulated wave action. Taphonomic damage is unlikely to be mistaken for drilling damage, due to the jagged, irregular appearance of taphonomically produced holes.     

Predatory behavior and preference of a successful invader, the mud crab Dyspanopeus sayi (Panopeidae), on its bivalve prey

Predator-prey relationships between the panopeid crab, Dyspanopeus sayi, and the mytilid, Musculista senhousia, were investigated. Through laboratory experiments, prey-handling behavior, prey size selection, predator foraging behavior and preferences for two types of prey (M. senhousia and the Manila clam Ruditapes philippinarum) were assessed. Handling time differed significantly with respect to the three prey sizes offered (small: 15.0-20.0 mm shell length, SL; medium: 20.1-25.0 mm SL; and large: 25.1-30.0 mm SL); mud crabs were more efficient in predating medium-small than large prey. Although differences in prey profitability were not evident, D. sayi exhibited a marked reluctance to feed on larger-sized prey whilst smaller, more easily predated mussels were available. Size selection may be the result of a mechanical process in which encountered prey are attacked but rejected if they remain unbroken after a certain number of opening attempts. D. sayi exhibited inverse density-dependent foraging. A significant higher mortality of prey was evident at low prey density. Thus, at low predator density, the D. sayi-M. senhousia interaction was a destabilizing type II functional response. Interference responses affected the magnitude of predation intensity by D. sayi on M. senhousia, since as the density of foraging crabs increased, their foraging success fell. At high density (4 crabs tank⁻¹), crabs engaged in a high amount of agonistic activity when encountering a conspecific specimen, greatly diminished prey mortality. Finally, presenting two types of prey, Manila clam juveniles were poorly predated by mud crabs, which focused their predation mostly on M. senhousia. It is hypothesized that, when more accessible prey is available, mud crabs will have a minimal predatory impact on commercial R. philippinarum juvenile stocks.     

Drilling predation on scaphopods and other molluscs from the Upper Cretaceous of Manitoba, Canada

Abundant information on drilling predation upon fossil bivalves, gastropods, and brachiopods has been accumulated during the past several decades, but very little is known about the predation on marine, infaunal carnivorous scaphopods. A survey of over 440 specimens of the scaphopod Dentalium gracile collected from the Upper Cretaceous Millwood Member (Campanian) of the Pierre Shale at a site near Russell, Manitoba displays a drilling percentage of approximately 35%. This figure is higher than previously reported for the scaphopods of similar age elsewhere, but is comparable to or lower than that of the sub-Holocene (34–61%). The difference in drilling percentage among different collections may be taxon-related or affected by the composition and structure of the fossil community. Morphologically, the drill-holes, produced by predatory drilling, are beveled with a countersunk profile of clean sharp edges. The drill-hole inner margin is ovate whereas the outer margin is nearly circular. Among the Manitoba specimens, drill-holes seem to be more common on the lateral side. Presumably due to the lack of effective defense strategy, the prey effectiveness is low (∼3.2%). There is no correlation between drill-hole dimension and scaphopod prey size, indicating that predator size does not correlate with the prey size. Nearly 480 specimens of cephalopods, pelecypods, and gastropods were also collected from the same community. There were only a total of 16 drill-holes on this additional material. Over 400 specimens of the only naticid Euspira obliquata were recovered from the same site and are believed to be the predators of the scaphopods and other molluscs. The low percentage (∼2.5%) of drilling on the abundant gastropod E. obliquata may indicate mistaken or opportunistic attacks by the predator, or that the cannibalism is not common in this community.     

Feeding behavior,ration and size structure of a population of the predatory gastropod <Emphasis Type="Italic">Cryptonatica janthostoma</Emphasis> in Vostok Bay,Sea of Japan

The relationships between the shell height of the predatory gastropod Cryptonatica janthostoma and the shell length of its typical prey, the bivalve Ruditapes philippinarum, and the diameter of the borehole on the prey shell resulting from a successful attack of the predator were experimentally found and assessed statistically. The shell height of C. janthostoma calculated retrospectively from the borehole diameter using the obtained relationships was 17–52 mm. The prey of C. janthostoma are burrowing bivalves, whose populations are affected by the predator to a varying degree. In populations of medium-sized mollusks (R. philippinarum, Protothaca euglypta, P. jedoensis, and others), C. janthostoma feeds on mollusks larger than 7–10 mm; in species with a shell length greater than 100 mm (Callista brevisiphonata, Saxidomus purpuratus), it eats specimens of 10–58 mm. C. janthostoma apparently has no effect on populations of small-sized mollusks (Anisocorbula venusta) and mollusks with an active avoidance response (Clinocardium californiense).     

Predator size and phenology shape prey survival in temporary ponds

Theoretical efforts suggest that the relative sizes of predators and their prey can shape community dynamics, the structure of food webs, and the evolution of life histories. However, much of this work has assumed static predator and prey body sizes. The timing of recruitment and the growth patterns of both predator and prey have the potential to modify the strength of predator–prey interactions. In this study, I examined how predator size dynamics in 40 temporary ponds over a 3-year period affected the survival of spotted salamander (Ambystoma maculatum) larvae. Across communities, gape-limited predator richness, but not size, was correlated with habitat duration (pond permanence). Within communities, mean gape-limited predator size diminished as the growing season progressed. This size reduction occurred because prey individuals grew into a body size refuge and because the largest of the predators left ponds by mid-season. Elevated gape-limited predation risk across time and space was predicted by the occurrence of two large predatory salamanders: marbled salamander larvae (Ambystoma opacum) and red-spotted newt adults (Notophthalmus viridescens). The presence of the largest gape-limited predator, A. opacum, predicted A. maculatum larval survival in the field. The distribution of large predatory salamanders among ponds and across time is expected to lead to differing community dynamics and to generate divergent natural selection on early growth and body size in A. maculatum. In general, a dynamic perspective on predator size often will be necessary to understand the ecology and evolution of species interactions. This will be especially true in frequently disturbed or seasonal habitats where phenology and ontogeny interact to determine body size asymmetries. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Additive interactions between the moon snail Euspira heros and the sea star Asterias forbesi, two predators of the surfclam Spisula solidissima

A laboratory experiment was conducted to determine whether the sea star Asterias forbesi and the naticid gastropod Euspira heros feed on surfclams, Spisula solidissima, in an additive or non-additive manner. Predators were allowed to feed on clams with conspecifics and in the presence of the other predator species. Clam mortality (measured as the rate of decline of clam number) and predator feeding rates were noted. To determine the effects of temperature on interactions among the predators, the experiment was conducted at three different temperatures. At all temperatures, feeding rate of each predator was not affected by the presence of the other species, and clam mortality in the presence of both predators was predictable from mortality in the presence of a single predator species. These additive interactions are most likely a result of habitat partitioning between the predators, with naticid snails being infaunal and sea stars being epifaunal. Previous studies in a variety of systems show no clear pattern of occurrence of non-additive interactions. Relatively small differences in predator or prey behavior may be responsible for the presence or absence of non-additive interactions. Received: 6 August 1998 / Accepted: 25 January 1999     

Experimental assessment of predation risk for juvenile green sturgeon,Acipenser medirostris,by two predatory fishes

Predation is a common cause of early life stage mortality in fishes, with reduced risk as individuals grow and become too large to be consumed by gape-limited predatory fishes. Large-bodied species, such as sturgeon, may reach this size-refuge within the first year. However, there is limited understanding of what this size threshold is despite the value of this information for conservation management. We conducted laboratory-based predation experiments on juvenile green sturgeon, Acipenser medirostris, to estimate vulnerability to predation during outmigration from their natal reaches in California to the Pacific Ocean. Two highly abundant and non-native predatory fish species (largemouth bass, Micropterus salmoides, and striped bass, Morone saxatilis) were captured in the wild to be tested with developing juvenile green sturgeon from the UC Davis Green Sturgeon Broodstock Program. Experimental tanks, each containing five predators, received thirty prey for 24-hr exposures. Between sturgeon prey trials, predators were exposed to alternative prey species to confirm predators were exhibiting normal feeding behaviors. In addition to green sturgeon mortality data, trials were video recorded and predatory behaviors were quantified. Overall, these predator species displayed much lower rates of predation on juvenile green sturgeon than alternate prey. Predation decreased with green sturgeon size, and predation risk diminished to zero once sturgeon reached a length threshold of roughly 20–22 cm total length, or between 38% and 58% of predator total length. Behavioral analyses showed low motivation to feed on green sturgeon, with both predators attempting predation less frequently as sturgeon grew. Results of this study imply that optimizing growth rates for larval and juvenile sturgeon would shorten the time in which they are vulnerable to predation. Future experiments should assess predation risk of juvenile green sturgeon by additional predator species common to the Sacramento-San Joaquin watershed.     

EVIDENCE FROM THE FOSSIL RECORD OF AN ANTIPREDATORY EXAPTATION: CONCHIOLIN LAYERS IN CORBULID BIVALVES

Conchiolin layers, organic-rich laminae, are characteristic of the shells of corbulid bivalves. The retention of these layers, despite their high metabolic cost, throughout the evolutionary history of Corbulidae has prompted the proposal of several adaptive scenarios to explain the origin and maintenance of these layers. The most widely held hypothesis contends that conchiolin layers are an adaptation for inhibiting drilling by predatory naticid gastropods. However, others suggest that the layers are adaptations to retard shell dissolution in waters undersaturated with calcium carbonate or to increase shell strength in the face of durophagous (shell crushing) predators. In this paper, experiments using recent Corbula (Varicorbula) gibba (Olivi) and observations of corbulids' present natural habitat demonstrate the current utility of conchiolin layers for all three functions: retardation of shell dissolution in waters undersaturated in calcium carbonate, increase of mechanical shell strength, and inhibition of drilling by predatory naticid gastropods. Earlier analyses of the extensive history of naticid predator-corbulid prey interactions suggested that conchiolin layers were an adaptation, a feature that promotes fitness and was built by selection for its current role, for deterring naticid predators. Not only are naticid drillholes widespread in fossil and recent corbulid shells, but an unusually large number of incomplete drillholes terminate unsuccessfully at conchiolin layers. In addition, a phylogenetic analysis of the origin of conchiolin layers and its function to deter naticid predators is consistent with a hypothesis of adaptation for this function. However, this hypothesis is rejected by an examination of fossil Jurassic Corbulomima. These oldest corbulids contained conchiolin layers before the evolution of naticid drilling during the Early Cretaceous. Therefore, conchiolin layers appear to be an exaptation, characters evolved for other usages and later “coopted” for their current role, for defense against drilling predators. The layers may in fact be an adaptation to resist durophagous predation.     

Traces of Naticid Predation on the Gryphaeid Oyster Pycnodonte dissimilaris: Epifaunal Drilling of Prey in the Paleocene

Traces of drilling predation by naticid gastropods were observed on 51 valves of the free-lying, semi-infaunal oyster Pycnodonte dissimilaris (Gryphaeidae) from the Paleocene Hornerstown Formation, in New Jersey. Stereotypic behavior of the predator is indicated by the highly constrained placement of drill holes, 94% of which are centrally located on the oyster shells. Predator—prey mismatches in size, involving small predators that drilled through the upper valves of relatively large oysters, are documented by comparison of outer borehole diameter, as an index of predator size, with the sizes of the oyster shells. Results of this analysis suggest that at least some prey were drilled epifaunally, as they were too large to be manipulated and buried by the predator. This indicates, together with reports of epifaunal drilling by living naticids, that such behavior is geographically and stratigraphically more widespread in the Naticidae than has previously been acknowledged. This in turn suggests that epifaunal drilling of prey is a plesiomorphic, opportunistic mode of behavior, conserved in the evolution of the Naticidae, that has permitted subsequent escalation or expansion in range of naticid foraging from a more narrowly defined infaunal paradigm into exposed intertidal refugia.     

Phenotypic plasticity in oysters (Crassostrea virginica) mediated by chemical signals from predators and injured prey

Prey organisms reduce predation risk by altering their behavior, morphology, or life history. Avoiding or deterring predators often incurs costs, such as reductions in growth or fecundity. Prey minimize costs by limiting predator avoidance or deterrence to situations that pose significant risk of injury or death, requiring them to gather information regarding the relative threat potential predators pose. Chemical cues are often used for risk evaluation, and we investigated morphological responses of oysters (Crassostrea virginica) to chemical cues from injured conspecifics, from heterospecifics, and from predatory blue crabs (Callinectes sapidus) reared on different diets. Previous studies found newly settled oysters reacted to crab predators by growing heavier, stronger shells, but that adult oysters did not. We exposed oysters at two size classes (newly settled oyster spat and juveniles ~2.0 cm) to predation risk cue treatments including predator or injured prey exudates and to seawater controls. Since both of the size classes tested can be eaten by blue crabs, we hypothesized that both would react to crab exudates by producing heavier, stronger shells. Oyster spat grew heavier shells that required significantly more force to break, an effective measure against predatory crabs, when exposed to chemical exudates from blue crabs as compared to controls. When exposed to chemical cues from injured conspecifics or from injured clams (Mercenaria mercenaria), a sympatric bivalve, shell mass and force were intermediate between predator treatments and controls, indicating that oysters react to injured prey cues but not as strongly as to cues released by predators. Juvenile oysters of ~ 2.0 cm did not significantly alter their shell morphology in any of the treatments. Thus, newly settled oysters can differentiate between predatory threats and adjust their responses accordingly, with the strongest responses being to exudates released by predators, but oysters of 2.0 cm and larger do not react morphologically to predatory threats.     

Effects of prey density,prey size and predator size on rates of feeding by an intertidal predatory gastropod Morula marginalba Blainville (Muricidae), on several species of prey

As a prerequisite for models of foraging behaviour of the whelk, Morula marginalba Blainville (Muricidae), the effects of variation in density of prey on the rate of feeding of the predator were examined in field conditions for three coexisting species of prey. Densities of prey used were those at which the prey, two limpets and a barnacle, occurred naturally in the rocky intertidal habitat.Large limpets, Cellana tramoserica (Sowerby) can resist attacks by predatory gastropods by raising the mantle over the outside of the shell. These experiments showed that no C. tramoserica were killed by Morula marginalba even at very great densities and with no alternative prey present. For the small limpet Patelloida latistrigata (Angas), one of the whelk's most highly preferred prey, juveniles were eaten 1.4 times as fast as adults. Fitting the random predator equation gave greater attack coefficients and shorter handling times for juvenile than adult limpets.Sizes of both predator and prey affected rates of eating barnacles, Tesseropora rosea (Krauss), but not in a simple way. Whelks of 15-mm aperture length ate adult barnacles 4.2 times faster than did 12-mm whelks, but there was no significant difference in the rates at which the two sizes of snail ate juvenile barnacles.Rates of feeding on T. rosea and Patelloida latistrigata increased significantly with prey density. These results form a basis for including the density of prey in models of spatial dispersion of the predatory gastropod Morula marginalba.     

Short-term hypoxia modulates Rapana venosa (Muricidae) prey preference in Adriatic lagoons

We studied the effect of short-term hypoxia on predation by the non-native rapa whelk (Rapana venosa) on the three most common bivalve prey in northern Adriatic lagoons: the non-native ark shell (Scapharca inaequivalvis) and Manila clam (Tapes philippinarum), and the native cockle Cerastoderma glaucum. In mesocosm experiments, bivalves were offered to predator as single prey, and as multiple choice of prey. Bivalve prey showed behavioral responses when exposed to short-term hypoxia. Under normoxia, prey were consumed in almost equal numbers when offered separately, but when choice was offered to the predator R. venosa showed a marked preference for S. inaequivalvis. Short-term hypoxia increased the vulnerability of T. philippinarum, and, consequently, rapa whelks modified their predatory behavior and switched their preference to T. philippinarum. We hypothesize this to be a case of environmentally-mediated, non-reciprocal indirect interaction between the two non-native prey species, whose causes are based upon differences in specific traits of prey. Hypoxia may facilitate the coexistence of the two non-native bivalves via predator switching. The native cockle seems the net loser of the game.     

Influence of prey body characteristics and performance on predator selection

At the time of settlement to the reef environment, coral reef fishes differ in a number of characteristics that may influence their survival during a predatory encounter. This study investigated the selective nature of predation by both a multi-species predator pool, and a single common predator (Pseudochromis fuscus), on the reef fish, Pomacentrus amboinensis. The study focused on the early post-settlement period of P. amboinensis, when mortality, and hence selection, is known to be highest. Correlations between nine different measures of body condition/performance were examined at the time of settlement, in order to elucidate the relationships between different traits. Single-predator (P. fuscus) choice trials were conducted in 57.4-l aquaria with respect to three different prey characteristics [standard length (SL), body weight and burst swimming speed], whilst multi-species trials were conducted on open patch reefs, manipulating prey body weight only. Relationships between the nine measures of condition/performance were generally poor, with the strongest correlations occurring between the morphological measures and within the performance measures. During aquaria trials, P. fuscus was found to be selective with respect to prey SL only, with larger individuals being selected significantly more often. Multi-species predator communities, however, were selective with respect to prey body weight, with heavier individuals being selected significantly more often than their lighter counterparts. Our results suggest that under controlled conditions, body length may be the most important prey characteristic influencing prey survival during predatory encounters with P. fuscus. In such cases, larger prey size may actually be a distinct disadvantage to survival. However, these relationships appear to be more complex under natural conditions, where the expression of prey characteristics, the selectivity fields of a number of different predators, their relative abundance, and the action of external environmental characteristics, may all influence which individuals survive.     

Putting prey and predator into the CO2 equation--qualitative and quantitative effects of ocean acidification on predator-prey interactions

Little is known about the impact of ocean acidification on predator-prey dynamics. Herein, we examined the effect of carbon dioxide (CO(2)) on both prey and predator by letting one predatory reef fish interact for 24 h with eight small or large juvenile damselfishes from four congeneric species. Both prey and predator were exposed to control or elevated levels of CO(2). Mortality rate and predator selectivity were compared across CO(2) treatments, prey size and species. Small juveniles of all species sustained greater mortality at high CO(2) levels, while large recruits were not affected. For large prey, the pattern of prey selectivity by predators was reversed under elevated CO(2). Our results demonstrate both quantitative and qualitative consumptive effects of CO(2) on small and larger damselfish recruits respectively, resulting from CO(2)-induced behavioural changes likely mediated by impaired neurological function. This study highlights the complexity of predicting the effects of climate change on coral reef ecosystems.     

A trait‐based approach reveals the feeding selectivity of a small endangered Mediterranean fish

Functional traits are growing in popularity in modern ecology, but feeding studies remain primarily rooted in a taxonomic‐based perspective. However, consumers do not have any reason to select their prey using a taxonomic criterion, and prey assemblages are variable in space and time, which makes taxon‐based studies assemblage‐specific. To illustrate the benefits of the trait‐based approach to assessing food choice, we studied the feeding ecology of the endangered freshwater fish Barbus meridionalis. We hypothesized that B. meridionalis is a selective predator which food choice depends on several prey morphological and behavioral traits, and thus, its top‐down pressure may lead to changes in the functional composition of in‐stream macroinvertebrate communities. Feeding selectivity was inferred by comparing taxonomic and functional composition (13 traits) between ingested and free‐living potential prey using the Jacob's electivity index. Our results showed that the fish diet was influenced by 10 of the 13 traits tested. Barbus meridionalis preferred prey with a potential size of 5–10 mm, with a medium–high drift tendency, and that drift during daylight. Potential prey with no body flexibility, conical shape, concealment traits (presence of nets and/or cases, or patterned coloration), and high aggregation tendency had a low predation risk. Similarly, surface swimmers and interstitial taxa were low vulnerable to predation. Feeding selectivity altered the functional composition of the macroinvertebrate communities. Fish absence favored taxa with weak aggregation tendency, weak flexibility, and a relatively large size (10–20 mm of potential size). Besides, predatory invertebrates may increase in fish absence. In conclusion, our study shows that the incorporation of the trait‐based approach in diet studies is a promising avenue to improve our mechanistic understanding of predator–prey interactions and to help predict the ecological outcomes of predator invasions and extinctions.