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How predator-prey mass ratios (PPMR) vary across taxa and body sizes has long-standing, unresolved relevance to ecosystem structure, function, and modeling. Mid-level fishes, or forage fishes, convey large amounts of trophic energy in coastal marine ecosystems, but uncertainty in the dependence of their PPMR on predator species and size hampers ecological understanding and model development. Late-summer (September) data (2000, 2001, and 2003) on three major zooplanktivorous forage fishes (capelin Mallotus catervarius, eulachon Thaleichthys pacificus, and juvenile walleye pollock Gadus chalcogrammus) in the western Gulf of Alaska, northeast Pacific Ocean, were used to determine how PPMR varied by species and body size. Differences in species' ability to transition across prey taxa were associated with different allometric relationships in prey size. Transitioning across taxa allowed prey size to increase hyperallometrically resulting in negative size dependence of PPMR for capelin and juvenile walleye pollock, both marine species. In contrast, eulachon, an anadromous species, consumed euphausiids almost exclusively and exhibited positive size dependence of PPMR. Our findings suggest that some predator species differ in transitioning across size-structured taxonomic groups of prey and consequently differ in their size-PPMR relationship. They also suggest that incorporation of taxon-specific PPMR size dependency into multispecies size-based ecosystem models will improve model realism partly because the PPMR is linked theoretically to trophic transfer efficiency., Author(s): Matthew T. Wilson [sup.1] , David G. Kimmel [sup.1] Author Affiliations: (1) grid.422706.5, 0000 0001 2168 7479, Alaska Fisheries Science Center, NOAA, , 7600 Sand Point Way NE, 98115, [...]

Evaluating the species-specific effects of multiple predators on shared prey helps to identify the mechanisms regulating predator impacts. Here, we investigate the trophic impact of two predators of the Chilean rocky subtidal, the fish Graus nigra [F] and the octopus Robsonella fontaniana [O] on their shared prey, the porcelain crab, Petrolisthes violaceus. Manipulative laboratory experiments were performed to evaluate mortality and behavior of porcelain crab in different treatments, including prey alone; prey with single predator ([O] or [F]); and prey with combined predators ([F + F], [O + O], and [O + F]). Different prey densities (N = 3, 9, and 12 individuals) were used to explore density-dependent predation mortality for single and combined predators using an orthogonal (crossed) design that allows to tease apart the effects of predator taxonomic identity from prey density. Behavioral responses of interacting species were registered every 4 h for 2 consecutive days, and were used to identify predator foraging strategies and prey refuge use. Mortality values (proportional prey mortality and predator per capita consumption) were compared among treatments. Results indicated differences in mortality among treatments. The cause of increase of prey proportional mortality was due to an increase in prey availability outside the refuge in fish treatments at high initial prey densities, while it was density independent in octopus' treatments. Changes in predator per capita consumption were registered depending on the predator combination and the initial prey density. These patterns may reflect contrasting predator foraging strategies and changes in refuge use by porcelain crabs, suggesting effects on prey mortality and predator impacts., Author(s): Rodrigo H Muñoz-Cordovez [sup.1] , Sergio A. Carrasco [sup.2] , F. Patricio Ojeda [sup.3] , Alejandro Pérez-Matus [sup.1] [sup.4] Author Affiliations: (1) grid.7870.8, 0000 0001 2157 0406, Subtidal Ecology [...]

Stable isotope analysis is increasingly used to investigate diet and foraging behaviour in marine wildlife. For marine mammals, samples from offspring are being used as proxies for their mothers foraging isotope niche as the transfer of nutrients between mother and neonates is solely through milk. Most of these proxy studies have, however, used only easily collected tissues, such as fur or whiskers. Quantifying the changes in [delta].sup.13C and [delta].sup.15N values between mother and pup requires the measurement of the mother/offspring pairs' milk and blood serum. Here, [delta].sup.13C and [delta].sup.15N values were measured from serum and milk samples from lactating New Zealand (NZ) sea lion, Phocarctos hookeri females and their pups. The change in [delta].sup.13C values between mother and pup serum averaged ~ 0.8â°. Whole milk was strongly [delta].sup.13C depleted compared to serum [delta].sup.13C values from either mothers or pups. The change in [delta].sup.15N values averaged 1.3â° between mother and pup serum, while differences in [delta].sup.15N values from whole milk to mother or pup serum averaged 0.4â° and 0.9â°, respectively. Lactating NZ sea lions are known to have two distinct foraging ecotypes which can be identified in their isotopic values and these differences could also be determined in the [delta].sup.15N values of milk and serum samples from their pups. Similar to other research, the findings confirm that changes in [delta].sup.13C and [delta].sup.15N between tissues of mothers and pups are species and tissue specific, and greater research is needed to understand their physiological and biochemical isotopic relationship., Author(s): B. Louise Chilvers [sup.1] Author Affiliations: (1) grid.148374.d, 0000 0001 0696 9806, Wildbase, School of Veterinary Science, Massey University, , Palmerston North, New Zealand Introduction The analysis of stable [...]

INTRODUCTION UNDERSTANDING THE CAUSES BEHIND population cycles has been a fundamental issue in ecology for decades (Krebs et al., 1995). Although a large body of literature exists on the subject [...]

Relationships between abundance--body size and trophic position--body size can reveal size structuring in food webs and test ecological theory. Although there is considerable evidence of size structuring in temperate aquatic food webs, little is known about the structure of tropical coral reef food webs. Here, we use underwater visual-census data and nitrogen stable isotope analysis to test if coral reef fish communities (i) are size structured and (ii) follow metabolic scaling rules. After examining individuals from over 160 species spanning four orders of magnitude in body size, we show that abundance scaled negatively with body size and, as predicted, individuals sharing energy through predation (carnivorous fishes) scaled more steeply than those individuals sharing a common energy source (herbivorous fishes). Estimated size spectra were, however, shallower than predicted by metabolic theory. Trophic position scaled positively with body size across species and across individuals, providing novel evidence of size structuring in a diverse tropical food web. Size-based approaches hold great promise for integrating the complexities of food webs into simple quantitative measures, thus providing new insights into the structure and function of aquatic ecosystems. Resume : Les relations entre abondance et taille du corps et entre position trophique et taille du corps peuvent reveler une structuration des tailles dans les reseaux trophiques et permettre de valider des theories ecologiques. Si la preuve a l'appui d'une structuration des tailles dans les reseaux trophiques aquatiques temperes est considerable, les connaissances sur la structure des reseaux trophiques de recifs de corail tropicaux sont tres limitees. Nous utilisons des donnees de recensement visuel sous l'eau et d'analyse des isotopes stables d'azote pour verifier si les communautes de poissons de recifs coralliens (i) sont structurees selon la taille et (ii) suivent des regles d'echelle metaboliques. L'examen d'individus de plus de 160 especes couvrant quatre ordres de grandeur de taille du corps demontre que l'abondance varie selon une relation d'echelle negative par rapport a la taille du corps et, comme prevu, les individus qui s'echangent de l'energie par l'entremise de la predation (les poissons carnivores) changent d'echelle plus abruptement que ceux qui partagent une meme source d'energie (les poissons herbivores). Les spectres de tailles estimes sont toutefois moins abrupts que le predit la theorie metabolique. L'echelle de position trophique est positivement reliee a la taille du corps pour toutes les especes et tous les individus, ce qui fournit de nouvelles preuves d'une structuration des tailles dans un reseau trophique tropical diversifie. Les approches basees sur la taille sont tres prometteuses pour ce qui est d'integrer les complexites des reseaux trophiques en des mesures quantitatives simples, jetant ainsi un nouvel eclairage sur la structure et la fonction des ecosystemes aquatiques. [Traduit par la Redaction], Introduction Elucidating the structure of natural food webs can provide fundamental insight into ecosystem dynamics, including energy fluxes (Lindeman 1942; Rooney et al. 2008), trophic cascades (Bascompte et al. 2005; [...]

ABSTRACT The wavy turban snail Megastraea undosa and keyhole limpet Megathura crenulata, two gastropods with commercial importance, five macroalgae, and one seagrass were collected at Bahia Tortugas, Baja California Sur, [...]

Small pelagic fish can play an important role in various ecosystems linking lower and upper trophic levels. Among the factor behind the observed inter-annual variations in small pelagic fish abundance, intra- and inter-specific trophic interactions could have a strong impact on the recruitment variability (e.g. anchovy). Egg cannibalism observed in anchovies has been postulated to be a mechanism that determines the upper limit of the population density and self-regulates the population abundance of the species. On the other hand, predation by other guild species is commonly considered as a regulation mechanism between competing species. This study provides empirical evidence of anchovy cannibalism and predation of the main small pelagic fish species on anchovy eggs and estimates the effect of intraguild predation on the anchovy egg mortality rate. Results show that, depending on the year (2008-2009), up to 33 % of the total anchovy egg mortality was the result of sardine predation and up to 4 % was the result of egg cannibalism together with predation by Atlantic and Atlantic Chub mackerel and sprat. Results also indicate that in the Bay of Biscay, fluctuations in the survival index of the early life stages of anchovy are likely to be attributable at least in part to egg cannibalism and especially to a high sardine predation on anchovy eggs., Author(s): Eneko Bachiller[sup.1] [sup.2] , Unai Cotano[sup.1] , Leire Ibaibarriaga[sup.1] , Maria Santos[sup.1] , Xabier Irigoien[sup.1] [sup.3] Author Affiliations: (1) Marine Research Division, AZTI Foundation, Herrera Kaia Portualdea z/g, 20110, [...]

This study used morphological, gut content analysis and carbon- and nitrogen-stable isotope analysis to investigate the trophic structure of upper sublittoral (15-30 m deep) and upper bathyal (200-300 m deep) hydrothermal vents and the adjacent non-vent upper bathyal environment off Kueishan Island. The sublittoral vents host no chemosynthetic fauna, but green and red algae, epibiotic biofilm on crustacean surfaces, and zooplankton form the base of the trophic system. Suspension-feeding sea anemones and the generalist omnivorous vent crab Xenograpsus testudinatus occupy higher trophic levels. The upper bathyal hydrothermal vent is a chemoautotrophic-based system. The vent mussel Bathymodiolus taiwanensis forms a chemosynthetic component of this trophic system. Bacterial biofilm, surface plankton, and algae form the other dietary fractions of the upper bathyal fauna. The vent hermit crab Paragiopagurus ventilatus and the vent crab X. testudinatus are generalist omnivores. The vent-endemic tonguefish Symphurus multimaculatus occupies the top level of the trophic system. The adjacent non-vent upper bathyal region contains decapod crustaceans, which function as either predators or scavengers. The assemblages of X. testudinatus from sublittoral and upper bathyal vents exhibited distinct stable isotope values, suggesting that they feed on different food sources. The upper bathyal Xenograpsus assemblages displayed large variations in their stable isotope values and exhibited an ontogenetic shift in their δ[sup.13]C and δ[sup.15]N stable isotope signatures. Some individuals of Xenograpsus exhibited δ[sup.15]N values close to those of non-vent species, suggesting that the highly mobile Xenograpsus may transfer energy between the upper bathyal hydrothermal vents and the adjacent non-vent upper bathyal environment., Introduction The deep-sea is an environment that does not receive solar radiation. Energy sources in the deep-sea are principal inputs from marine snow (i.e. organic matter and plankton) sinking from [...]

Gorgonians are widespread sub-littoral benthic suspension feeders in the world oceans. However, data on their trophic ecology and role in benthic-pelagic coupling and biogeochemical cycles remain limited. This study assesses the trophic ecology of Leptogorgia virgulata in the Skidaway River estuary, USA (31.9896N, 81.0242W) by analysing carbon and nitrogen isotopic signatures of its soft tissue and different-sized fractions of particulate organic matter (POM) in its environment. Samples were taken in 5 April, 2 August, and 15 October 2012 and 11 January 2013. Results support a distinct temporal shift in the diet of L. virgulata from the POM fraction, Introduction Benthic suspension feeders (BSF) play a key role in population and community ecology of shallow littoral ecosystems because they are abundant and create habitat niches for numerous organisms (Gili [...]

Common carp Cyprinus carpio is a ubiquitous invasive species that commonly imposes negative effects on aquatic ecosystems. However, research evaluating the effects of carp on native fishes is limited. Carp are highly fecund and larvae and juveniles can be abundant. If age-0 carp use similar prey resources as native fishes, they may compete if food becomes limited. We used traditional diet analysis for samples during Jul. and Aug. 2008 in Brant Lake. Stable isotopes were used for samples collected during Aug. and Sep. 2009 in Brant Lake and Lake Sinai to examine prey resource use by age-0 carp and four native fishes: bluegill Lepomis macrochims, black crappie Pomoxis nigromaculatus, yellow perch Perea flavescens, and orangespotted sunfish Lepomis humilis. Age-0 carp were generally as or more abundant than native fishes. In Jul. Daphnia dominated the diets of all fishes sampled, resulting in high (>60%) dietary overlap ranging from 87-98%. In Aug. Daphnia density in Brant Lake declined and dominant diet prey types shifted for carp (to Trichoptera and Daphnia), yellow perch (to Amphipoda), and the three Centrarchids (to Cyclops and Diaptomus). This diet shift resulted in lower diet overlap between Centrarchids and either carp (, INTRODUCTION Translocation of species outside of their native range often occurs without an adequate understanding of the implications of such introductions on native fauna. Introductions and invasions of nonnative species [...]

Knowing the trophic ecology of marine predators is essential to develop an understanding of their ecological role in ecosystems. research conducted on deep-sea and threatened shark species is limited. Here, by combining analyses of individual stomach contents and stable isotope values, we examined the trophic ecology (dietary composition and trophic position) of the kitefin shark Dalatias licha, a deep-sea shark considered as near threatened globally and as data deficient in the Mediterranean Sea. results revealed the importance of small sharks in the diet of the kitefin shark at short- and long-term scales, although finfish, crustaceans and cephalopods were also found. Predation on sharks reveals the high trophic position of the kitefin shark within the food web of the western Mediterranean Sea. Stable isotope values from liver and muscle tissues confirmed our results from stomach content analysis and the high trophic position., Introduction Determining the feeding ecology of a particular organism is essential to understanding its ecological role in the ecosystem. Sharks are often classified as top predators within marine ecosystems, although [...]

We utilised stable isotope ratios to assess differences in diet among three indigenous and syntopic rocky shore suspension-feeders (mussels Perna perna, barnacles Tetraclita serrata, and polychaetes Gunnarea gaimardi). We also determined the spatial and temporal variability in the suspension-feeder diets by collecting specimens on two occasions from two regions adjacent to hydrologically distinct river mouths (i.e. one with larger annual freshwater throughput than the other). The results showed that the isotopic niches (used as proxies for trophic niches) of the three species did not overlap and that the barnacles occupied a trophic position (3.4) well above those of the mussels (2) and polychaetes (2.6). We ascribed the interspecific differences primarily to the disparate feeding mechanisms used by the species. Large-scale regional (~50 km) differences in suspension-feeder diets were apparent, but not small-scale (up to a few km north and south of each estuary mouth). The regional differences in diet resulted from the increased availability of estuarine-origin suspended particulate matter (SPM) and zooplankton in the region adjacent to the river with relatively larger freshwater output, although overall incorporation of zooplankton versus mixed SPM into consumer diets was relatively consistent between regions and through time. Temporal shifts in suspension-feeder diets were apparent from stable carbon isotope ratios in the consumers. Our results showcase the measurable effects of regional-scale processes that can alter the food sources for dominant primary consumers in the rocky intertidal, thus potentially affecting entire food webs through bottom-up processes. The clear evidence for trophic niche partitioning offers valuable insights into how potentially strong competitors can coexist., Introduction Suspension-feeders on rocky shores are exposed to a rich variety of food sources, the composition and quality of which can change markedly through space and time (Bode et al. [...]

Variable ocean conditions can greatly impact prey assemblages and predator foraging in marine ecosystems. Our goal was to better understand how a change in ocean conditions influenced dietary niche overlap among a suite of midtrophic-level predators. We examined the diets of three fishes and one seabird off central Oregon during two boreal summer upwelling periods with contrasting El Nino (2010) and La Nina (2011) conditions. We found greater niche specialization during El Nino and increased niche overlap during La Nina in both the nekton and micronekton diet components, especially in the larger, more offshore predators. However, only the two smaller, more nearshore predators exhibited interannual variation in diet composition. Concurrent trawl surveys confirmed that changes in components of predator diets reflected changes in the prey community. Using multiple predators across diverse taxa and life histories provided a comprehensive understanding of food-web dynamics during changing ocean conditions., Introduction Although ecological theory predicts that predators would have specialized foraging strategies to avoid direct competition with one another when food resources are limited (Schoener 1971; Greene 1986), many marine […]

Multivariate analysis of fatty acids (FA) profiles proved to be a useful tool for demonstrating feeding preferences of Arctic invertebrates belonging to several taxonomic groups collected during summer and winter seasons in the Spitsbergen fjords (Arctic). Within phytodetrivorous taxa, the enhanced proportions of 16:1n-7, C16 polyunsaturated fatty acids (PUFA) and 20:5n-3 in crustaceans clearly reflected selective ingestion of diatoms, while high amounts of 22:6n-3 and C18 FAs found in molluscs indicated flagellate-based nutrition. High levels of C20 PUFA and 16:1n-7 together with the typical bacterial FAs were found in winter specimens of deposit-feeding polychaetes showing their reliance on highly reworked organic matter during this season. Our results suggest that 18:1n-9 may not be a reliable marker of carnivory feeding within benthic taxa. Lipid signatures of omnivores and carnivores/detrivores usually originated from a variety of dietary sources, of which few possess highly characteristic FA features. Still, elevated levels of Calanus markers (20:1 and 22:1 moieties) characterized species linked to the pelagic food chains, while 20:4n-6 proved to be a useful indicator of foraminiferan consumption. We highlight the need for a multimethod approach, since complexity of benthic food webs along with general lack of unambiguous FA trophic markers prevents tracking of trophic relationships with use of FA analysis alone. Based on their FA composition, we showed that benthic species represent a source of essential PUFA and could play a fundamental role in the Arctic food webs transferring energy derived from variable pelagic and benthic resources to upper trophic levels., Introduction Improved knowledge of the spatial distribution and functional roles of marine organisms is required to understand energy flow through food webs, and to better predict climate-related fluctuations and human-induced [...]

The trophic niche is an aspect of species biology that is foundational to understanding many biological processes. In coastal marine ecosystems, small schooling fishes have a large influence on food web dynamics and structure, but despite their importance, the trophic niches of many of these fishes are either completely unknown or only preliminarily described. We assembled a diet dataset for 12 species of small, coastal Indo-Pacific clupeoids (herrings, sardines, and anchovies) containing measurements of 12,401 prey items from 619 individual fish predators to address four objectives: (1) assign species to trophic guilds based upon prey-type and -size consumption, (2) identify ontogenetic shifts in prey-type and -size consumption, (3) test the hypotheses that niche breadth, measured as the range of prey sizes consumed, and relative niche breadth (ratio of niche breadth to predator size) are positively correlated with predator size, and (4) test the hypotheses that maximum prey-size consumption and relative maximum prey-size consumption (ratio of maximum prey size to predator size) are positively correlated with predator size. We identified three and five trophic guilds based upon prey types and prey sizes, respectively. Diets changed through ontogeny in nearly every species. Linear regression revealed positive correlations between niche breadth, maximum prey width, and relative maximum prey width and predator size, but did not find a statistically significant correlation between relative niche breadth and predator size. This study shows that measuring prey size in addition to prey type can offer additional, higher resolution information about fish trophic ecology. The dataset presented here will be useful for future ecological and evolutionary research and fisheries management., Author(s): Joshua P. Egan [sup.1] [sup.2] , Sean Gibbs [sup.3] , Andrew M. Simons [sup.2] [sup.3] Author Affiliations: (Aff1) 0000000419368657, grid.17635.36, Conservation Sciences Graduate Program, University of Minnesota, , 135B [...]

Stable isotope ratios (SIR) are widely used to estimate food-web trophic levels (TLs). We built systems dynamic N-biomass-based models of different levels of complexity, containing explicit descriptions of isotope fractionation and of trophic level. The values of [delta].sup.15N and TLs, as independent and emergent properties, were used to test the potential for the SIR of nutrients, primary producers, consumers, and detritus to align with food-web TLs. Our analysis shows that there is no universal relationship between TL and [delta].sup.15N that permits a robust prognostic tool for configuration of food webs even if all system components can be reliably analysed. The predictive capability is confounded by prior dietary preference, intra-guild predation and recycling of biomass through detritus. These matters affect the dynamics of both the TLs and SIR. While SIR data alone have poor explanatory power, they would be valuable for validating the construction and functioning of dynamic models. This requires construction of coupled system dynamic models that describe bulk elemental distribution with an explicit description of isotope discriminations within and amongst functional groups and nutrient pools, as used here. Only adequately configured models would be able to explain both the bulk elemental distributions and the SIR data. Such an approach would provide a powerful test of the whole model, integrating changing abiotic and biotic events across time and space., Author(s): Kevin J. Flynn [sup.1] , Aditee Mitra [sup.1] , Antonio Bode [sup.2] Author Affiliations: (Aff1) 0000 0001 0658 8800, grid.4827.9, Biosciences, Swansea University, , Singleton Park, SA2 8PP, Swansea, [...]

When an ecosystem model of the North Sea is calibrated to data from multiple trophic levels, the model estimated the primary production required to support the food web correlates temporally with observed changes in sea temperature and nutrient levels, supporting evidence from empirical analyses. However, a different result is given from an alternative calibration using fish stock data only. The inference taken from the emergent primary production--temperature relationship and empirical data are that, on balance, there is stronger overall evidence to support the calibration constrained at multiple trophic levels. Two important implications of the findings are (i) that the relative importance of fishing and environmental effects is likely to be interpreted differently depending on the calibration approach and (ii) the contrasting model calibrations would give different responses to fishing policies. It raises questions regarding how to judge the performance (and credibility) of an ecosystem model and the critical importance of conducting empirical and modelling analyses in parallel. Adopting a combined approach to ecosystem modelling is an important step in the pursuit of operational and defensible tools to support the ecosystem approach to management. Quand un modele d'ecosysteme de la mer du Nord est cale sur des donnees provenant de differents niveaux trophiques, l'estimation de la production primaire necessaire pour supporter le reseau trophique produite par ce modele est correlee dans le temps aux changements observes de la temperature de la mer et des teneurs en nutriments, appuyant les resultats decoulant d'analyses empiriques. Une autre approche de calage reposant uniquement sur des donnees sur les stocks de poissons donne toutefois un resultat different. La conclusion decoulant de la relation emergente entre production primaire et temperature et des donnees empiriques est que, dans l'ensemble, les donnees appuient plus fortement le calage sur des donnees provenant de differents niveaux trophiques. Deux importantes conclusions decoulent de ces resultats, a savoir que (i) l'importance relative de la peche et d'effets du milieu peut etre interpretee differemment selon l'approche de calage et (ii) differentes approches de calage de modele meneraient a differentes conclusions quant aux consequences de politiques sur la peche. Cela souleve des questions concernant l'evaluation de la performance (et de la credibilite) des modeles d'ecosysteme et l'importance capitale de realiser parallelement des analyses empiriques et de modelisation. L'adoption d'une approche combinee de modelisation de l'ecosysteme constitue un important pas vers l'elaboration d'outils efficaces et defendables pour appuyer une approche ecosystemique de gestion. [Traduit par la Redaction], Introduction Empirical evidence shows that climate driven changes in ocean conditions have a widespread influence on biological components throughout North Atlantic ecosystems (Ottersen et al. 2001). Both direct and indirect [...]

The relative contribution of kelps and other food sources to the diet of consumers in shallow coastal communities has been hotly debated in recent years. It has been suggested that considering proxies instead of phytoplankton isotopic signatures can lead to an overestimation of kelp contribution through isotopic mixing models. We analysed spatial patterns in carbon isotopic ratios of the dominant primary sources and consumers at two subtidal sites in Brittany (France) prior to the anticipated 2011 phytoplankton bloom to determine which of kelp and phytoplankton is the dominant food source in Laminaria hyperborea forests. We found simultaneous spatial variations for consumers, kelps and deposited particulate organic matter, suggesting that kelp-derived organic matter is a key component of associated food webs for at least part of the year., Introduction Stable isotopes have been used increasingly over the last few decades to characterize the relative contribution of kelp and phytoplankton to the diet of suspension feeders in shallow coastal [...]

Abstract--Stable isotope (SI) values of carbon (δ[sup.13]C) and nitrogen (δ[sup.15]N) are useful for determining the trophic connectivity between species within an ecosystem, but interpretation of these data involves important assumptions [...]