Ontogenetic Diet Shifts Research Articles

Mandibular force profiles and tooth morphology in growth series of Albertosaurus sarcophagus and Gorgosaurus libratus (Tyrannosauridae: Albertosaurinae) provide evidence for an ontogenetic dietary shift in tyrannosaurids1

The albertosaurines Albertosaurus sarcophagus and Gorgosaurus libratus are among the best represented tyrannosaurids, known from nearly complete growth series. These specimens provide an opportunity to study mandibular biomechanical properties and tooth morphology to infer changes in feeding behaviour and bite force through ontogeny in tyrannosaurids. Mandibular force profiles reveal that the symphyseal region of albertosaurines is consistently stronger in bending than the mid-dentary region, indicating that the anterior extremity of the jaws played an important role in prey capture and handling through ontogeny. The symphyseal region was better adapted to withstand torsional stresses than in most non-avian theropods, but not to the extent seen in Tyrannosaurus rex, suggesting that albertosaurine feeding behaviour may have involved less bone crushing or perhaps relatively smaller prey than in Tyrannosaurus rex. The constancy of these biomechanical properties at all known growth stages indicates that although albertosaurines maintained a similar feeding strategy through ontogeny, prey size/type had to change between juvenile and mature individuals. This ontogenetic dietary shift likely happened when individuals reached a mandibular length of ∼58 cm, a size at which teeth shift from ziphodont to incrassate in shape and bite force begins to increase exponentially. The fact that large albertosaurines were capable of generating bite forces equivalent to similar-sized tyrannosaurines suggests that no significant differences in jaw-closing musculature existed between the two clades and that the powerful bite of Tyrannosaurus rex is the result of its large body size rather than of unique adaptations related to a specialized ecology.

Life history of

Mustelus mustelus from the Langebaan Marine Protected Area (LMPA) has been largely protected from fishing activities for the past 30 years; therefore, its biology represents those of an unfished stock. The reproductive biology, diet, growth and maturity of M. mustelus was studied in the Langebaan Lagoon region in the south-western Cape Coast of South Africa between 2007 and 2009. In total, 217 sharks (females: 381–1734 mm total length (TL); males: 467–1267 mm TL) were examined. Sharks in the Bay represented the largest specimens among six regions, globally. Female parturition, ovulating and mating occurred between November and December after a gestation period of 10–11 months. No ontogenetic shift in diet was evident, with the diet predominantly consisting of the following three species of crustaceans; Hymenosoma orbiculare, Upogebia africana and Callichirus kraussi. The von Bertalanffy growth parameters for combined sexes were L∞ = 1594 mm TL, k = 0.15 year–1, t0 = –2.01 year (n = 95). Possible age over-estimation was investigated using micro-computed tomography, which highlighted the existence of false check marks. This study indicated that the LMPA represents a pupping, nursery and feeding ground as well as a refuge area for the largest and oldest recorded smoothhound sharks globally, emphasising its importance in spatial conservation of this species.

Validating the use of bulk tissue stable isotope and amino acid δ15N values measured in molted hair and epidermis of elephant seals to assess temporal foraging niche specialization

The degree of dietary generalization versus specialization exhibited by populations can impact their ability to respond to changing environmental conditions. Naturally shed hair and epidermis are easily collected and may provide a suitable substrate for stable isotope analysis to assess trophic niche specialization. Whether fasting influences the isotopic composition of molted tissues has not been assessed. Here, we gauged the validity of using carbon (δ13C) and nitrogen (δ15N) isotope analysis of molted hair and the outermost epidermis as proxies to study the foraging ecology of southern elephant seals Mirounga leonina at Marion Island in the southern Indian Ocean. Similarity in both bulk tissue (δ13C and δ15N) and amino acid (δ15N) isotope values of molted tissues and whiskers known to reflect fasting confirmed that physiological changes associated with fasting influenced hair and epidermis isotope values. We recommend caution when using the isotopic composition of molted hair and epidermis to make ecological inferences regarding diet and/or movement. Despite these limitations, molted hair can be used to detect extreme foraging behaviors, which we show using an extensive data set of hair sampled from marked individuals (n = 331) that hauled out on Marion Island during the 2012-2013 annual pelage molt. Other factors, such as ontogenetic shifts in diet and potential environmental (baseline) isotopic variation, also influence hair δ13C and δ15N values, which complicates the use of isotopic data from molted tissues to assess the temporal consistency of an individuals’ isotopic niche.

Interactive effects of body size and environmental gradient on the trophic ecology of sea stars in an Antarctic fjord

Antarctic sea stars can occupy different trophic niches and display different trophic levels, but, while the impacts of their body size and environmental features on their trophic niches are potentially important, they are presently understudied. Here we assessed the trophic ecology in relation to the size and habitat of sea stars in a fjord on King George Island (South Shetland Islands) using stable isotope values of carbon (δ13C), nitrogen (δ15N), and sulphur (δ34S). The disc radius influenced δ13C and δ15N values, whereas more limited changes in δ13C or δ34S values were related to arm length. Specifically, δ13C and δ15N values were linked to disc radius in generalist species (Diplasterias brandti and Odontaster validus), which could indicate ontogenetic diet shifts, while this relationship occurred less frequently in more specialised species (Bathybiaster loripes, Notasterias bongraini, and Perknaster sladeni). O. validus had a smaller isotopic niche size in the inner than the outer fjord. The niche overlap between D. brandti and O. validus was low in the inner fjord. Low resource availability within the fjord, linked to higher turbidity, could induce trophic niche constriction and interspecific resource segregation. This could represent a mechanism for competition avoidance in a resource-limited system. Conversely, higher resource availability could allow O. validus to expand and share its isotopic niche with D. brandti in the outer fjord with a limited risk of competition. This trophic plasticity will likely influence how O. validus copes with the present and future modification of environmental conditions induced by climate change.

Ontogenetic diet shifts: an additional mechanism for successful invasion of a piranha species in a Neotropical floodplain.

Ontogenetic shifts in food preference reduces intraspecific competition as immature individuals eat different food types than adults. This diet plasticity could facilitate species' ability to successfully invade and establish itself in a new environment, even when co-occurring with phylogenetically close species. Here, ontogenetic diet shifts of a non-native piranha species (Serrasalmus marginatus) was tested by analyzing the relationship between its body length and the carbon and nitrogen stable isotope signatures. Carbon stable isotope was not correlated to fish length, but positive significant correlation between δ15N values and fish length was found for the non-native piranha. Also, immature and adult S. marginatus showed low isotopic niche overlap. The correlation between fish length and δ15N, and the low trophic overlap between immature and adult, indicate that the non-native S. marginatus had ontogenetic shifts in food preference, which may be viewed as an additional mechanism underlying its successful establishment in the upper Paraná River. Our findings indicate that ontogenetic shifts in food preference may be an invasive trait that facilitates the establishment of non-native fish species in tropical aquatic systems.

Seasonal feeding habits and ontogenetic diet shift of black bullhead (Ameiurus melas) in Lake Sava (Serbia)

The black bullhead is an invasive species that forms dense populations and has a negative impact on the native ichthyofauna. Recent studies indicate that it is one of the most dominant invasive fish species in Serbian waters. Feeding habits based on stomach contents of individuals caught in Lake Sava were analyzed as a first step towards evaluating its possible negative impact on the native fish fauna of the lake. The following indices for diet analysis were applied: vacuity index, frequency of occurrence, numerical abundance and prominence value. Trophic niche breadth and seasonal trophic diversity were calculated using the Shannon?s index. The diet spectrum comprised 16 different prey categories from five groups: Mollusca, Crustacea, Insecta, Teleostei and plants. Fish were the main prey in all seasons, followed by aquatic invertebrates. Plant material and terrestrial insects were used as food in relatively small quantities. Predation on fish eggs was also detected. Our research confirmed that this species is an opportunistic generalist. An ontogenetic diet shift was also detected. The lowest value of trophic diversity was found in age 1+ individuals (H=1.39), while the highest was found in age 3+ individuals (H=2.00). The widest niche breadth was recorded in spring 2011 (H=2.12).

Feeding habits of Urotrygon microphthalmum (Myliobatiformes: Urotrygonidae) caught off northeastern Brazil

Abstract The feeding habits of Urotrygon microphthalmum, a Critically Endangered (CR) species, were investigated through stomach contents analysis from specimens caught on bottom double rigged otter trawls in Pernambuco state, Brazil, between March of 2010 and March of 2012. A total of 338 stomachs were analyzed, and 31 food items were identified in the diet of U. microphthalmum. The species ingests mainly shrimps. The diets between males and females were not different, and an ontogenetic diet shift was not observed. The estimated species’ trophic level is 3.5, classifying it as a secondary order consumer.

Ontogenetic shift in the diet of Dajaus monticola (Mugiliformes: Mugilidae) with comments in the recruitment of young individuals in the Honduran Caribbean coast

ABSTRACT Studies have been devoted to describing the diet of D. monticola. However, knowledge of how D. monticola utilizes food resources through ontogeny remains unknown. We characterized D. monticola general dietary patterns and tested for ontogenetic diet shifts. We also inferred on juvenile recruitment patterns. We examined the stomach contents of 120 specimens ranging in size from 20 to 154 mm in standard length (SL). To infer on recruitment periodicity, we examined the size of specimens deposited in museum collections to compile size frequencies by month. We assume that the occurrence of smaller-size class categories will shed light on their recruitment time. Our results show that D. monticola is an omnivore that largely feeds on aquatic insects but also includes detritus, terrestrial material, fishes and crustaceans. Our analysis did not detect strong changes in diet through ontogeny, instead some changes were detected but mainly on the percentage of some food items included at different size category classes. In regards to the recruitment periodicity, we found younger D. monticola (20–40 mm SL) throughout most of the year, suggesting that they may be reproducing for longer periods of time than those previously reported from Honduras.

Variability of isotopic partitioning between sympatric brown trout (Salmo trutta) and European grayling (Thymallus thymallus) in the Loue River (France)

AbstractTrophic partitioning, defining how individuals or populations differ in their resource use, is expected to promote coexistence of sympatric species by reducing resource overlap. We used stable isotope measurements (δ13C and δ15N) to address niche characteristics (δ13C and δ15N ranges, isotope convex hull and standard ellipse areas, mean nearest neighbour distances and trophic positions) and trophic partitioning of sympatric brown trout (Salmo trutta,n = 110) and European grayling (Thymallus thymallus,n = 63) in two sampling locations of a French river. Aquatic resources predominantly fuelled both species, yet both terrestrial resources (TER) and trophic positions (TP) were higher for trout (~36 ± 13% TER, 3.6 ± 0.7 TP) than grayling (~26 ± 9% TER, 2.7 ± 0.6 TP) supporting difference in their trophic niches. Isotope analyses showed that trout had a larger isotope niche than grayling suggesting more opportunistic trophic behaviour. Their isotopic overlapping was higher at the upstream site (isotopic nestedness = 0.8 ± 0.1) than that at the downstream site (isotopic nestedness = 0.4 ± 0.2). Euclidian distances of stable isotopes and TP for the two species increased with salmonid size, while aquatic resource use decreased with salmonid size. These results demonstrate an increase in isotopic niche partitioning and change in trophic attributes with ontogeny. Our study showed that despite relying on similar resources, these two sympatric salmonids exhibited clear trophic differences that were amplified with ontogeny. The consideration of fish ontogenetic dietary shift would hence be a determinant driver of the trophic niche partitioning for these sympatric salmonids.

Ontogenetic resource use and trophic dynamics of endangered juvenile Tachypleus tridentatus among diversified nursery habitats in the northern Beibu Gulf, China.

Horseshoe crabs, the most well-known example of "living fossils", are iconic and ecologically important macroinvertebrates in coastal and estuarine ecosystems. Their blood is a crucial resource for manufacturing Limulus or Tachypleus amebocyte lysate to detect bacterial endotoxins or fungal contamination in drug and medical devices. An enhanced understanding of their ecological roles and trophic interactions in the food webs is fundamental to facilitate resource management for the declining populations in Asia. Foraging information of the Asian species, however, is mainly derived from preliminary, scattered reports from a limited number of study locations. In this study, resource utilization, trophic niche dynamics, and trophic interaction of the juvenile tri-spine horseshoe crab, Tachypleus tridentatus (instars 1-12, approximately 0.5-8years old) across ontogeny was assessed in diversified nursery habitats along the northern Beibu Gulf, China, using carbon and nitrogen stable isotopes. Our results suggest that: (i) T. tridentatus are ecological generalists given the vast range of carbon isotopic values and trophic niche width estimates exhibited between multiple instar groups; (ii) juvenile T. tridentatus across most habitat types predominantly assimilated energy from a variety of basal production sources in the food web, but primarily depended on sedimentary organic matter and seagrass resource pools; (iii) ontogenetic shifts in juvenile dietary proportions were evident, with decreased reliance on sedimentary organic matter, coupled with increased reliance on benthic macroinvertebrate grazers, detritivores, and omnivores with age; and (iv) nearly all juvenile instars occupied similar trophic positions in the food web with slight shifts in trophic position present with increasing size. Our findings indicate that resource availability and ontogenetic diet shifts strongly influence horseshoe crab trophic dynamics, and age should be accounted when formulating habitat conservation measures based on resource use for Asian horseshoe crabs.

Diet composition and feeding strategy of crossbanded barb, Puntioplites bulu (Bleeker, 1851) in Perak River, Peninsular Malaysia

Diet composition and feeding strategy of crossbanded barb, Puntioplites bulu caught from Perak, Malaysia from October 2015 to October 2016 were studied in relation to size and stages. Based on the stomach contents of 256 individuals with total length of 13.5 to 37.5 cm, 5.47% were empty. Puntioplites bulu showed omnivorous feeding habits. Fed mostly on benthic plant materials (mostly algae) and aquatic invertebrate. Diet of P. bulu were primarily comprised of Bacillariophyceae, Chlorophyceae, crustacea, mollusca and plant matter. Estimation based on Schoener’s index showed high overlap dietary items between juvenile and adult stages, however ontogenetic shifts in diet were observed between these two stages. Adult P. bulu fed on varieties of items in prey size range whereas juveniles on smaller items. The stage based diet variances suggest that mouth gape and swimming ability may influence on the feeding habits of P. bulu. Description of dietary items and feeding strategy can offer an insight for proper management of this species particularly for aquaculture and conservation purposes.

Separation of realized ecological niche axes among sympatric tilefishes provides insight into potential drivers of co-occurrence in the NW Atlantic.

Golden and Blueline Tilefish (Lopholatilus chamaeleonticeps and Caulolatilus microps) are keystone taxa in northwest (NW) Atlantic continental shelf‐edge environments due to their biotic (trophic‐mediated) and abiotic (ecosystem engineering) functional roles combined with high‐value fisheries. Despite this importance, the ecological niche dynamics (i.e., those relating to trophic behavior and food‐web interactions) of these sympatric species are poorly understood, knowledge of which may be consequential for maintaining both ecosystem function and fishery sustainability. We used stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) to build realized ecological niche hypervolumes to serve as proxies for diet and production use patterns of L. chamaeleonticeps and C. microps. We hypothesized that: (a) species exhibit ontogenetic shifts in diet and use of production sources; (b) species acquire energy from spatially distinct resource pools that reflect a sedentary life‐history and differential use of the continental shelf‐edge; and (c) species exhibit differentiation in one or more measured niche axes. We found evidence for ontogenetic shifts in diet (δ15N) but not production source (δ13C) in both species, suggesting a subtle expansion of measured ecological niche axes. Spatial interpolation of stable isotope ratios showed distinct latitudinal gradients; for example, individuals were 13C enriched in northern and 15N enriched in southern regions, supporting the assertion that tilefish species acquire energy from regional resource pools. High isotopic overlap was observed among species (≥82%); however, when hypervolumes included depth and region of capture, overlap among species substantially decreased to overlap estimates of 15%–77%. This suggests that spatial segregation could alleviate potential competition for resources among tilefish species inhabiting continental shelf‐edge environments. Importantly, our results question the consensus interpretation of isotopic overlap estimates as representative of direct competition among species for shared resources or habitats, instead identifying habitat segregation as a possible mechanism for coexistence of tilefish species in the NW Atlantic.

Habitat utilization and feeding ecology of small round goby in a shallow brackish lagoon

We examined small-scale distribution and feeding ecology of a non-native fish species, round goby (Neogobius melanostomus (Pallas, 1814)), in different habitats of a coastal lagoon situated in the south-western Baltic Sea. First observations of round goby in this lagoon were reported in 2011, 3 years before the current study was conducted, and information on this species’ basic ecology in different habitats is limited. We found that mainly juvenile round gobies are non-randomly distributed between habitats and that abundances potentially correlate positively with vegetation density and thus structural complexity of the environment. Abundances were highest in shallower, more densely vegetated habitats indicating that these areas might act as a refuge for small round gobies by possibly offering decreased predation risk and better feeding resources. Round goby diet composition was distinct for several length classes suggesting an ontogenetic diet shift concerning crustacean prey taxa between small (≤ 50 mm total length, feeding mainly on zooplankton) and medium individuals (51–100 mm, feeding mainly on benthic crustaceans) and another diet shift of increasing molluscivory with increasing body size across all length classes. Differences in round goby diet between habitats within the smallest length class might potentially be related to prey availability in the environment, which would point to an opportunistic feeding strategy. Here, we offer new insights into the basic ecology of round goby in littoral habitats, providing a better understanding of the ecological role of this invasive species in its non-native range, which might help to assess potential consequences for native fauna and ecosystems.

Ontogenetic diet shifts with potential ramifications for resource competition in a kokanee–Mysis diluviana system

Ontogenetic shifts represent important transitions that can influence how fish interact with their environment. However, ontogenetic shifts are rarely placed into a population context due to the difficulty of incorporating the vagaries of size-mediated interactions. As such, we evaluated the role of ontogenetic shifts in diet as they relate to potential competitive interactions between kokanee Oncorhynchus nerka and Opossum Shrimp Mysis diluviana (hereafter Mysis) in Lake Pend Oreille, Idaho. Contemporary data were used to understand diet patterns of Mysis and kokanee. Historical data were evaluated within the context of ontogenetic shifts to better understand the long-term, population-level ramifications of interactions between Mysis and kokanee. Diet analysis revealed age-specific divergences in diet whereby juvenile kokanee primarily consumed copepods and adult kokanee preferentially consumed cladocerans. When placed in a historical context, age-specific patterns in kokanee diet likely led to increases in adult growth following declines in Mysis abundance. Improved fitness of adult fish likely resulted in record high abundances of kokanee in Lake Pend Oreille thereby shifting the balance from inter- to intraspecific competition.

Differential ontogenetic effects of gut passage through fish on seed germination

Passage through the digestive tract of frugivorous vertebrates likely influences seed dormancy, time to germination, and/or future seedling growth. Effects of gut passage on seed germination have been extensively investigated among frugivorous birds and mammals, however, few studies have focused on frugivorous fish. Here we present the results of a feeding experiment focusing on a broadly distributed Amazonian frugivorous fish, Brycon falcatus, and a fig tree, Ficus gomelleira. We investigated the effects of gut passage and ontogeny on seed germination probability and speed. The probability of seed germination and germination speed increased for seeds defecated by fish relative to control seeds. We also detected a negative effect of intestine length, where germination probability and speed decreased when seeds passed through larger fish with greater intestine to body length ratio. Such effects are probably the result of ontogenetic diet shifts, in which young fish transition from carnivory to frugivory as adults; a process only revealed by the inclusion of both small juvenile and large adult individuals in our study. As such, we advance knowledge of the mechanisms involved in frugivory as a feeding habit among fishes and on animal-fruit mutualisms.

Contrasting size and fate of juvenile crown-of-thorns starfish linked to ontogenetic diet shifts

Population dynamics of organisms are shaped by the variation in phenotypic traits, often expressed even among individuals from the same cohort. For example, individual variation in the timing of ontogenetic shifts in diet and/or habitat greatly influences subsequent growth and survival of some organisms, with critical effects on population dynamics. Few studies of natural systems have, however, demonstrated that marked phenotypic variation in growth rates or body size among individuals within a modelled cohort is linked to dietary shifts and food availability. Population irruptions of the crown-of-thorns starfish are one of the foremost contributors to the global degradation of coral reefs, but causes of irruptions have been debated for decades. Here we demonstrate, based on extensive field sampling of juvenile starfish (n = 3532), that marked variation in body size among juvenile starfish is linked to an ontogenetic diet shift from coralline algae to coral. This transition in diet leads to exponential growth in juveniles and is essential for individuals to reach maturity. Because smaller individuals experience higher mortality and growth is stunted on an algal diet, the ontogenetic shift to corallivory enhances individual fitness and replenishment success. Our findings suggest that the availability of coral prey facilitates early ontogenetic diet shifts and may be fundamental in initiating population irruptions.

Trophic Ecology of the Cuban Boa, Chilabothrus angulifer (Boidae)

The Cuban Boa (Chilabothrus angulifer) is a top terrestrial predator in Cuba. References to prey species consumed by this boa date to when the first Europeans arrived in the region more than 500 years ago. However, long-term studies on its trophic ecology do not exist. The scarce and scattered records on its feeding habits indicate that this boa preys on a variety of native and domestic animals. Based on dietary information collected in the field and from the literature, we characterized the diet of this snake and tested four different hypotheses: (1) The Cuban Boa is a generalist predator; (2) the diets of boas in natural and anthropogenic habitats differ; (3) an ontogenetic shift in diet occurs; and (4) foraging strategies used in natural and anthropogenic habitats differ. We identified 49 prey species from 351 prey items obtained from 218 snakes, including 71 items (31 snakes) from the literature. Mammals represented 55% of total prey items consumed, followed by birds (41%) and ectotherms (4%). Chilabothrus angulifer exhibited a narrow niche breadth. However, rather than a trophic specialist, we consider this boa an opportunistic generalist predator, capable of adjusting its diet and foraging behavior according to prey availability and abundance. The diet of Ch. angulifer changed dramatically from mostly native mammals and birds in natural habitats to mostly livestock, pets, and human com­mensals in human-altered habitats. Also, mammals were consumed more frequently in natural habitats, whereas birds dominated the diet of boas associated with anthropogenic habitats. Few ectotherms were consumed in either type of habitat. We observed an ontogenetic shift in diet, but this primarily reflected a trend of consuming larger prey rather than a shift from ectotherms to endotherms as reported for some other boids. In natural habitats, Ch. angulifer used both ambush and active-foraging modes by day and night, whereas in anthropogenic situations, most boas used an active-foraging strategy at night. The frequent consumption of domestic animals by Cuban Boas might be the principal reason for the historical human-wildlife conflict involving this species in rural areas of Cuba.

Developmental ecomorphology of the epibranchial organ of the silver carp, Hypophthalmichthys molitrix.

Silver carp regularly consume and digest particles of food as small as 5 μm. This ability drives their efficient consumption of phytoplankton and because they feed low on the food chain they have an important place in aquaculture worldwide. In North America, where they are considered invasive, silver carp deplete food resources for native species and in so doing occupy increased niche space. Here, we determine the ontogenetic stage and size at which silver carp are morphologically capable of primarily feeding on particles <10 μm. Ecological studies on this species have shown that there is an ontogenetic shift in diet as predominantly zooplanktivorous juveniles later switch to eating much smaller phytoplankton. The occupation of this new trophic niche presents both a metabolic and a mechanical challenge to these fish, since it is unclear how they can efficiently feed on such small particles. We hypothesize that the epibranchial organ (EBO) in silver carp is essential in aggregating these small particles of food, allowing the species to consume mass quantities of tiny particles, thus mitigating metabolic constraints. In this study, we investigate early ontogeny of the EBO in silver carp to determine when this structure achieves the requisite morphology to become functional. We find that at around 80 mm standard length (SL) the EBOs are consistently filled with food, demonstrating that this accumulating organ has become functional. This size corresponds with previous ecological data documenting important shifts in the type of food consumed. While the basic bauplan of the EBO is established very early in ontogeny (by 15 mm SL), multiple waves of histological maturation of muscle, cartilage, gill rakers and epithelium ultimately form the functional structure.

Feeding ecology and microplastic ingestion in Chelon richardsonii (Mugilidae) associated with surf diatom Anaulus australis accumulations in a warm temperate South African surf zone

The study aimed to explore ontogenetic dietary changes and microplastic ingestion in Chelon richardsonii associated with diatom Anaulus australis accumulations in a warm temperate South African surf zone. This species is commercially important and forms an important trophic link in southern African coastal waters. Postflexion larvae, juveniles and adults are dominant in surf zones and were used for comparison. Index of Relative Importance (%IRI) results showed an ontogenetic dietary shift, with postflexion larvae ingesting mostly copepods (%IRI = 52.0) and microplastic fibres (%IRI = 30.7); while older developmental stages fed predominantly on diatoms (%IRI ranging from 53.9 to 65.6) and sand (%IRI ranging from 34.2 to 46.0). Microplastic fibres were found in 40% of fish sampled, microplastic fragments in 5%, and both types were recorded across all developmental stages assessed. This study provides the first record of microplastics in C. richardsonii, adding to growing microplastic research in fishes.

Ontogenetic trophic segregation between two threatened smooth-hound sharks in the Central Mediterranean Sea

Elasmobranchs are among the species most threatened by overfishing and a large body of evidence reports their decline around the world. As they are large predators occupying the highest levels of marine food webs, their removal can alter the trophic web dynamic through predatory release effects and trophic cascade. Suitable management of threatened shark species requires a good understanding of their behaviour and feeding ecology. In this study we provide one of the first assessments of the trophic ecology of the “vulnerable” smooth-hounds Mustelus mustelus and M. punctulatus in the Central Mediterranean Sea, based on stomach contents and stable isotope analyses. Ontogenetic diet changes were addressed by comparing the feeding habits of three groups of individuals: juveniles, maturing and adults. Our results highlighted that the two species share a similar diet based mostly on the consumption of benthic crustaceans (e.g. hermit crabs). Their trophic level increases during ontogeny, with adults increasing their consumption of large-sized crustaceans (e.g. Calappa granulata, Palinurus elephas), cephalopods (e.g. Octopus vulgaris) and fish (e.g. Trachurus trachurus). Our results provide also evidence of ontogenetic shifts in diet for both species showing a progressive reduction of interspecific trophic overlap during growth. The results of this study contribute to improve the current knowledge on the trophic ecology of these two threatened sharks in the Strait of Sicily, thus providing a better understanding of their role in the food web.