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Abstract

Spiny lobsters (P. penicillatus, P. longipes and P. versicolor) are heavily dependent on habitats like coral reefs, known to be highly vulnerable to climate change-driven degradation. Yet, little is known about their trophic ecology and their adaptive capacity to a changing environment. In this study, we used fatty acids (FA) analysed in the hepatopancreas and δ13C and δ15N stable isotopes analysed in the tail muscle of three spiny lobster species from the Seychelles coastal waters to (1) infer habitat use, dietary patterns and potential for resource competition and (2) investigate the effects of reef type and coral bleaching on their trophic niche metrics. We found that there was a potential for interspecific competition between the three species, shown by their high dietary overlap (mean FA niche overlap ranging from 71.2% to 99.5% for P. longipes and P. versicolor in P. penicillatus) and similar habitat use (δ13C value ranges). P. penicillatus, the largest of the three species, was more a generalist than the two other species (i.e., had a larger FA niche) and P. versicolor seemed to feed on smaller/earlier life stage prey than P. longipes (based on differences in δ15N values). The potential for resource competition of Seychelles spiny lobsters appeared higher in granite than carbonate reefs, and in post-2016 coral bleaching reefs. Our results suggest that P. penicillatus could have a greater adaptive capacity to climate change due to its higher dietary plasticity and that competition between Seychelles spiny lobsters may increase in the future as the frequency and severity of bleaching events is predicted to increase with climate change.

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... Les niches isotopiques individuelles des deux phoques veaux-marins et des deux phoques gris, pour lesquels des mesures complémentaires de δ 34 S ont été acquises sur les vibrisses, ont espèce/de la population, a ici été testé sur les valeurs conjointes de δ 13 C, δ 15 N et de δ 34 S mesurées sur les vibrisses des quatre individus choisis. Dans le cas présent, les niches isotopiques individuelles ont été évaluées en prenant en compte un niveau de variabilité intra-individuel.Les niches individuelles ont été représentées de façon synthétique en calculant une « ellipse moyenne » et deux « ellipses d'incertitudes », déterminées par application de moyennes sur les coordonnées d'ellipses choisies (voir la méthode présentée parSabino et al. 2021, dont le script R associé est disponible sur GitHub 3 ). Les deux ellipses d'incertitudes ont ici été déterminées en calculant la moyenne des 10% d'ellipses de plus petites aires et des 10% d'ellipses de plus grandes aires, et l'ellipse moyenne a été déterminée par la moyenne de toutes les ellipses. ...
Thesis
Le phoque veau-marin (Phoca vitulina) et le phoque gris (Halichoerus grypus), deux espèces sympatriques de mammifères marins, sont de plus en plus considérés comme des compétiteurs potentiels, et ce plus particulièrement au cœur de leur distribution européenne. L’objectif de cette thèse est d’étudier les stratégies de chasse et l’écologie trophique de ces espèces en limite de leur aire de distribution (baie de Somme, Manche Est, France), et d’explorer l’hypothèse de compétition interspécifique. Des outils de bio-télémétrie ont été déployés sur 49 individus afin d’obtenir des données sur leurs déplacements et plongées en mer. L’analyse des localisations en surface et du comportement en plongée, complétée plus récemment par la détection de tentatives de captures de proies (accélérométrie), a permis de mieux comprendre les stratégies de chasse de ces espèces, et d’améliorer la détection des zones de chasse. Les niches trophiques des deux espèces de phoques ont ensuite été caractérisées par analyse du régime alimentaire, des isotopes stables (vibrisses des mêmes individus capturés), et des zones de chasse. Un important chevauchement interspécifique a été identifié entre ces niches, résultant de la consommation de poissons plats benthiques en zone côtière, ce qui apporte ici le contexte informatif d’une potentielle compétition. Cette étude montre aussi le rôle clé des stratégies individuelles de chasse sur les conclusions écologiques à l’échelle de l’espèce/sous-population,dont la potentielle compétition qui serait induite par certains phoques gris. La poursuite des suivis est nécessaire pour détecter tout potentiel changement écologique dont l’origine serait trophique.
... Removal of lipids and urea before the C and N isotope analysis is recommended to avoid biased results due to lipids being more depleted in 13 C than other tissue components and to urea being more depleted in 15 N (Li et al., 2016;Logan et al., 2008;Post et al., 2007). In this study, spiny lobsters characterised by a low fat content in the tail muscle (mean of 0.74 ± 0.14 % wet weight; Sabino et al., 2021), were analysed directly for stable isotopes (bulk δ 13 C and δ 15 N values), while δ 13 C corresponded to lipidnormalised values for all other species, and δ 15 N corresponded to urea-normalised values for shark species. ...
Article
The concentrations of 13 trace elements were determined in 1032 muscles of 54 small-scale fisheries species collected from the Seychelles waters between 2013 and 2019. Overall, profiles were dominated by zinc (Zn) > arsenic (As) > iron (Fe) > copper (Cu) > selenium (Se), with the spiny lobsters, spanner crab and octopus exhibiting the highest levels of As, Cu and Zn while fish had higher Fe concentrations. Both taxonomy-dependent processes and ecological factors explained the interspecific differences of trace element profiles observed. A benefit-risk assessment revealed that crustaceans and cephalopods were good sources of Cu and Zn. One portion of any fish could provide 30–100 % of daily Se needs, and one portion of demersal and pelagic teleost fish could bring 5–20 % of Cu, Fe and Zn needs, especially for young adult and adult women. Finally, our analysis showed that there was very low health risks associated with small-scale fisheries consumption for the Seychelles population.
... Although we found that J. edwardsii improves resilience to future ocean warming, by energy-conserving metabolic adjustments, this did not improve physiological performance relative to a novel range-shifting competitor, the eastern rock lobster S. verreauxi. This subtropical species increasingly co-occurs in the resident temperate habitat of J. edwardsii (Fig. 1) and will likely compete for shelter and/or food 84,85 , particularly in resource impoverished localities 86 , such as recently formed urchin-dominated barren habitats 83 . In addition to the fact that S. verreauxi grows faster and much larger 46 , we found that it consistently matches or exceeds physiological and escape performance of J. edwardsii between 14 and 21 °C, which included higher maximum metabolic rate, aerobic scope, escape frequency and speed (Fig. 4, Table 2). ...
Article
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Marine species not only suffer from direct effects of warming oceans but also indirectly via the emergence of novel species interactions. While metabolic adjustments can be crucial to improve resilience to warming, it is largely unknown if this improves performance relative to novel competitors. We aimed to identify if spiny lobsters—inhabiting a global warming and species re-distribution hotspot—align their metabolic performance to improve resilience to both warming and novel species interactions. We measured metabolic and escape capacity of two Australian spiny lobsters, resident Jasus edwardsii and the range-shifting Sagmariasus verreauxi, acclimated to current average—(14.0 °C), current summer—(17.5 °C) and projected future summer—(21.5 °C) habitat temperatures. We found that both species decreased their standard metabolic rate with increased acclimation temperature, while sustaining their scope for aerobic metabolism. However, the resident lobster showed reduced anaerobic escape performance at warmer temperatures and failed to match the metabolic capacity of the range-shifting lobster. We conclude that although resident spiny lobsters optimise metabolism in response to seasonal and future temperature changes, they may be unable to physiologically outperform their range-shifting competitors. This highlights the critical importance of exploring direct as well as indirect effects of temperature changes to understand climate change impacts.
... Les niches isotopiques individuelles des deux phoques veaux-marins et des deux phoques gris, pour lesquels des mesures complémentaires de δ 34 S ont été acquises sur les vibrisses, ont espèce/de la population, a ici été testé sur les valeurs conjointes de δ 13 C, δ 15 N et de δ 34 S mesurées sur les vibrisses des quatre individus choisis. Dans le cas présent, les niches isotopiques individuelles ont été évaluées en prenant en compte un niveau de variabilité intra-individuel.Les niches individuelles ont été représentées de façon synthétique en calculant une « ellipse moyenne » et deux « ellipses d'incertitudes », déterminées par application de moyennes sur les coordonnées d'ellipses choisies (voir la méthode présentée parSabino et al. 2021, dont le script R associé est disponible sur GitHub 3 ). Les deux ellipses d'incertitudes ont ici été déterminées en calculant la moyenne des 10% d'ellipses de plus petites aires et des 10% d'ellipses de plus grandes aires, et l'ellipse moyenne a été déterminée par la moyenne de toutes les ellipses. ...
Thesis
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[ENGLISH ABSTRACT] Harbour seal (Phoca vitulina) and grey seal (Halichoerus grypus) are two sympatric marine mammal species that are increasingly considered as potential competitors, especially at their European core distributions. The objective of this PhD was to study the foraging strategies and trophic ecology of these species at the limit of their range (Baie de Somme, Eastern English Channel, France), and to investigate the hypothesis of potential interspecific competition. Bio-telemetry devices were fitted on 49 individuals to document their movements and dives at sea. The analysis of surface locations and diving behaviour, completed recently by the detection of Prey Capture Attempts (accelerometry), allowed for a better understanding of the two seal species’ foraging strategies and improved the detection of their foraging areas. Trophic niches of the two seal species were then characterised with the analysis of diet, stable isotopes (in the whiskers of the same captured individuals), and foraging areas. A high interspecific trophic overlap was identified between these niches, resulting from the consumption of benthic flatfish in coastal areas, and we suggest that it provides here the basis for potential competition between both species. This study also showed the key role of individual foraging strategies on the ecological conclusions at the scale of the species/sub-population, including that the potential competition may be due to some individual grey seal strategies. Continuing these studies is essential to detect any potential ecological changes that could be trophically-induced. ——— [FRENCH ABSTRACT] Le phoque veau-marin (Phoca vitulina) et le phoque gris (Halichoerus grypus), deux espèces sympatriques de mammifères marins, sont de plus en plus considérés comme des compétiteurs potentiels, et ce plus particulièrement au cœur de leur distribution européenne. L’objectif de cette thèse est d’étudier les stratégies de chasse et l’écologie trophique de ces espèces en limite de leur aire de distribution (baie de Somme, Manche Est, France), et d’explorer l’hypothèse de compétition interspécifique. Des outils de bio-télémétrie ont été déployés sur 49 individus afin d’obtenir des données sur leurs déplacements et plongées en mer. L’analyse des localisations en surface et du comportement en plongée, complétée plus récemment par la détection de tentatives de captures de proies (accélérométrie), a permis de mieux comprendre les stratégies de chasse de ces espèces, et d’améliorer la détection des zones de chasse. Les niches trophiques des deux espèces de phoques ont ensuite été caractérisées par analyse du régime alimentaire, des isotopes stables (vibrisses des mêmes individus capturés), et des zones de chasse. Un important chevauchement interspécifique a été identifié entre ces niches, résultant de la consommation de poissons plats benthiques en zone côtière, ce qui apporte ici le contexte informatif d’une potentielle compétition. Cette étude montre aussi le rôle clé des stratégies individuelles de chasse sur les conclusions écologiques à l’échelle de l’espèce/sous-population, dont la potentielle compétition qui serait induite par certains phoques gris. La poursuite des suivis est nécessaire pour détecter tout potentiel changement écologique dont l’origine serait trophique.
... Competition between spiny lobsters has been observed where shelter is limited or of insufficient quality (Eggleston et al. 1990, Briones-Fourzán et al. 2007). Resource competition between spiny lobsters will be further enhanced in degraded reef habitats, such as coral reefs following bleaching (Sabino et al. 2021). Such habitat degradation is particularly problematic in Tasmanian waters, where ocean warming and the arrival of the range-extending destructive longspined sea urchin Centrostephanus rodgersii has converted formerly rich underwater kelp forests to impoverished barren habitats (Johnson et al. 2005, Ling et al. 2015. ...
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Species redistributions are one of the most prevalent changes observed in oceans worldwide due to climate change. One of the major challenges is being able to predict temperature-driven changes to species interactions and the outcome of these changes for marine communities due to the complex nature of indirect effects. In the ocean-warming hotspot of south-east Australia, the ranges of many species have shifted poleward. The range of the eastern rock lobster Sagmariasus verreauxi has extended into warming Tasmanian waters inhabited by the resident southern rock lobster Jasus edwardsii , which may lead to increased competitive interactions between the species. Using video monitoring, we investigated how the 2 species compete for food at current (18°C), future (21°C) and future heatwave (24°C) summer temperatures. Behavioural competition occurred in 80% of experiments, during which J. edwardsii won 84% of competitive interactions and showed more aggressive behaviour at all temperatures. This indicates that resident J. edwardsii is not only more dominant in direct food competition than the range-shifting S. verreauxi but, surprisingly, also sustains competitive dominance beyond its physiological thermal optimum under predicted future ocean warming and heatwave scenarios.
Preprint
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Marine species not only suffer from direct effects of warming oceans but also indirectly via the emergence of novel species interactions. While metabolic adjustments can be crucial to improve resilience to warming, it is largely unknown if this improves performance relative to novel competitors. We aimed to identify if spiny lobsters – inhabiting a global warming and species re-distribution hotspot - align their metabolic performance to improve resilience to both warming and novel species interactions. We measured metabolic and escape capacity of two Australian spiny lobsters, resident Jasus edwardsii and the range-shifting Sagmariasus verreauxi, acclimated to current average- (14.0°C), current summer- (17.5°C) and projected future summer- (21.5°C) habitat temperatures. We found that both species decreased their standard metabolic rate with increased acclimation temperature, while sustaining their scope for aerobic metabolism. However, the resident lobster showed reduced anaerobic escape performance at warmer temperatures and failed to match the metabolic capacity of the range-shifting lobster. We conclude that although resident spiny lobsters optimise metabolism in response to seasonal and future temperature changes, they may be unable to physiologically outperform their range-shifting competitors. This highlights the critical importance of exploring direct as well as indirect effects of temperature changes to understand climate change impacts.
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Models of biomass size spectra assume that organisms with higher body mass feed at higher trophic levels, but explicit empirical tests of this pattern are rare. We used nitrogen stable isotopes (delta(15)N) as an index of the trophic level in a benthic fish and invertebrate size-spectrum, and demonstrated that body mass was Positively and significantly related to trophic level. This pattern was consistent with the expectation that predator-prey relationships led to powerful size-based trophic structuring in marine communities and ecosystems, Further analysis of intra- and interspecific relationships between body mass and trophic level in the community showed that increases in trophic level across the size spectrum were predominantly a consequence of intra-specific increases in trophic level with body mass and not a consequence of larger species (species with greater maximum body mass) feeding at higher trophic levels, We confirmed the absence of strong inter-specific relationships between maximum body mass and trophic level with cross-species and phylogenetic comparative approaches. Size-based models are easier and cheaper to parameterise than most food-web models. Subject to the persistence of relationships between body mass and trophic level in space and time, our results suggest that size spectra could be parameterised with body mass-trophic level relationships and used to describe the trophic structure of some marine communities and ecosystems.
Article
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The composition of lipids and fatty acids was determined for the livers, muscle, pancreas, kidney and stomach fluids of deepwater chondrichthyan species (including 11 squaliformes, 3 chimaeriformes, 1 hexanchiforme and 3 carcharhiniformes) caught as bycatch from continental waters off south-eastern Australia. The lipid class, fatty acid and fatty alcohol composition differed markedly in each tissue and in each species. The lipid and fatty acid composition of large, lipid-rich (38–70% wet weight, ww) livers demonstrated the multifunctional role of this organ in: lipid distribution, storage and biosynthesis, and buoyancy regulation. In the liver, the importance of certain lipids (including squalene, diacylglyceryl ethers, triacylglycerols and to a lesser extent wax esters) as mediators of buoyancy varied according to lifestyle and habitat. Less variability was observed in the muscle profiles, characterized by low lipid content (<1.0% ww) and high relative levels of polar lipids (>70%). The lipid and fatty acid profiles of the kidney and pancreas showed the highest intraspecific variability, suggesting these organs also have complex roles in lipid storage and metabolism. Overall intra- and interspecific differences in the tissue fatty acid profiles could be related to differences in a number of factors including phylogeny, habitat (depth), buoyancy regulation and diet and presumably also reflect different ecological roles. The lipid and fatty acid profiles are the first published for Rhinochimaera pacifica, Chimaera lignaria and Figaro boardmani and the first to demonstrate interspecific variation in lipid profiles of various tissues of deepwater chondrichthyans. The application of multivariate analysis to lipid class and fatty acid tissue profiles in chondrichthyans inferred dietary differences and metabolic preferences between species and habitats. These results have important implications for the future use of fatty acids as dietary tracers in chondrichthyan research.
Chapter
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Food web structure, predator–prey dynamics, foraging behavior, and consequences of these factors for individual growth, reproduction and survival are central to our understanding of ecosystem structure and functioning. Moreover, in the current context of understanding (and managing) ecosystems in the face of ongoing environmental change, important questions include: What are the critical prey of key consumers in relation to prey abundance, availability, and nutritional quality? What are the ecosystem processes responsible for food web production? And, how do these processes respond to changes in physical forcing? A fundamental require-ment to understand any of these areas is an accurate assessment of trophic relationships and consumer diets. However, in aquatic, and especially marine ecosystems, such information is generally not easily or reliably obtained. In these systems, the relative inaccessibility of free-ranging organisms and the inability to directly observe species interactions make it difficult to accurately characterize diet. Traditional approaches, such as examining gut contents, have well-recognized biases in addition to representing only snapshots of recent meals and may therefore not be reliable indicators of long-term diet (Iverson et al. 2004). Thus, alternative approaches have been developed, which use various types of trophic markers. One of the most promising of these approaches is the use of lipids and fatty acids (FA) to study food web dynamics.
Article
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The stable isotopes of nitrogen (d15N) and carbon (d13C) provide powerful tools for estimating the trophic positions of and carbon flow to consumers in food webs; however, the isotopic signature of a consumer alone is not generally sufficient to infer trophic position or carbon source without an appropriate isotopic baseline. In this paper, I develop and discuss methods for generating an isotopic baseline and evaluate the assump- tions required to estimate the trophic position of consumers using stable isotopes in multiple ecosystem studies. I test the ability of two primary consumers, surface-grazing snails and filter-feeding mussels, to capture the spatial and temporal variation at the base of aquatic food webs. I find that snails reflect the isotopic signature of the base of the littoral food web, mussels reflect the isotopic signature of the pelagic food web, and together they provide a good isotopic baseline for estimating trophic position of secondary or higher trophic level consumers in lake ecosystems. Then, using data from 25 north temperate lakes, I evaluate how d 15N and d13C of the base of aquatic food webs varies both among lakes and between the littoral and pelagic food webs within lakes. Using data from the literature, I show that the mean trophic fractionation of d15N is 3.4‰ (1 SD 5 1‰) and of d13 Ci s 0.4‰ (1 SD 5 1.3‰), and that both, even though variable, are widely applicable. A sen- sitivity analysis reveals that estimates of trophic position are very sensitive to assumptions about the trophic fractionation of d15N, moderately sensitive to different methods for gen- erating an isotopic baseline, and not sensitive to assumptions about the trophic fractionation of d13C when d13C is used to estimate the proportion of nitrogen in a consumer derived from two sources. Finally, I compare my recommendations for generating an isotopic baseline to an alternative model proposed by M. J. Vander Zanden and J. B. Rasmussen. With an appropriate isotopic baseline and an appreciation of the underlying assumptions and model sensitivity, stable isotopes can help answer some of the most difficult questions
Article
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Prey in natural communities are usually shared by many predator species. How predators coexist while competing for the same prey is one of the fundamental questions in ecology. Here, we show that competing predator species may not only coexist on a single prey but even help each other to persist if they specialize on different life history stages of the prey. By changing the prey size distribution, a predator species may in fact increase the amount of prey available for its competitor. Surprisingly, a predator may not be able to persist at all unless its competitor is also present. The competitor thus significantly increases the range of conditions for which a particular predator can persist. This “emergent facilitation” is a long-term, population-level effect that results from asymmetric increases in the rate of prey maturation and reproduction when predation relaxes competition among prey. Emergent facilitation explains observations of correlated increases of predators on small and large conspecific prey as well as concordance in their distribution patterns. Our results suggest that emergent facilitation may promote the occurrence of complex, stable, community food webs and that persistence of these communities could critically depend on diversity within predator guilds. • emergent facilitation • food-dependent prey development • predator coexistence • prey stage • stage-specific predation
Article
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Within an organism, lipids are depleted in 13C relative to proteins and carbohydrates (more negative δ13C), and variation in lipid content among organisms or among tissue types has the potential to introduce considerable bias into stable isotope analyses that use δ13C. Despite the potential for introduced error, there is no consensus on the need to account for lipids in stable isotope analyses. Here we address two questions: (1) If and when is it important to account for the effects of variation in lipid content on δ13C? (2) If it is important, which method(s) are reliable and robust for dealing with lipid variation? We evaluated the reliability of direct chemical extraction, which physically removes lipids from samples, and mathematical normalization, which uses the carbon-to-nitrogen (C:N) ratio of a sample to normalize δ13C after analysis by measuring the lipid content, the C:N ratio, and the effect of lipid content on δ13C (Δδ13C) of plants and animals with a wide range of lipid contents. For animals, we found strong relationships between C:N and lipid content, between lipid content and Δδ13C, and between C:N and Δδ13C. For plants, C:N was not a good predictor of lipid content or Δδ13C, but we found a strong relationship between carbon content and lipid content, lipid content and Δδ13C, and between and carbon content and Δδ13C. Our results indicate that lipid extraction or normalization is most important when lipid content is variable among consumers of interest or between consumers and end members, and when differences in δ13C between end members is 13C fall within these criteria. Both direct lipid extraction and mathematical normalization reduce biases in δ13C, but mathematical normalization simplifies sample preparation and better preserves the integrity of samples for δ15N analysis.
Article
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Dietary diversity often varies inversely with prey resource abundance. This pattern, although typically measured at the population level, is usually assumed to also characterize the behavior of individual animals within the population. However, the pattern might also be produced by changes in the degree of variation among individuals. Here we report on dietary and associated behavioral changes that occurred with the experimental translocation of sea otters from a food-poor to a food-rich environment. Although the diets of all individuals were broadly similar in the food-rich environment, a behaviorally based dietary polymorphism existed in the food-poor environment. Higher dietary diversity under low resource abundance was largely driven by greater variation among individuals. We further show that the dietary polymorphism in the food-poor environment included a broad suite of correlated behavioral variables and that the individuals that comprised specific behavioral clusters benefited from improved foraging efficiency on their individually preferred prey. Our findings add to the growing list of examples of extreme individuality in behavior and prey choice within populations and suggest that this phenomenon can emerge as a behavioral manifestation of increased population density. Individuality in foraging behavior adds complexity to both the fitness consequences of prey selection and food web dynamics, and it may figure prominently as a diversifying process over evolutionary timescales. • foraging efficiency • niche width • polymorphism • prey handling
Article
Spiny lobsters (Panulirus longipes, P. penicillatus and P. versicolor) are an important resource in Seychelles, where they inhabit coastal carbonate and granite reefs that have been impacted by multiple coral bleaching events over the past two decades. Little is known about their biology and ecology in this region. Interspecific competition for food resources was previously suggested, but no quantitative data on the diets of spiny lobsters were available. Using carbon and nitrogen stable isotope compositions and fatty acid profiles of three spiny lobster species and their potential prey, a Bayesian mixing model for diet estimation was applied to compare the diet proportions of spiny lobsters among species and between reef types (carbonate and granite reefs). Model outputs suggested the three lobster species consume mainly crustaceans (Anomoura hermit crabs; half of the diet), then Echinoidea (sea urchins), algae and molluscs. P. versicolor was found to consume slightly more molluscs and algae than the two other studied species, which was consistent with its lower trophic level (2.4 vs 2.8 for the two other species). Trophic level did not increase with carapace length of spiny lobsters, but large individuals had higher carbon isotopic values suggesting that they might feed closer to the coast or more on detritus feeders than their smaller congeners. Diets of spiny lobsters were fairly similar between carbonate and granite reefs, except that lobster inhabiting granite reefs consumed more sea urchins. While our overall findings were consistent with gut contents of Panulirus spp. from other world regions, they should be confirmed, as the discrimination of several prey based on trophic tracers was low, which increased mixing model uncertainty.
Article
Specialist individuals within animal populations have shown to be more efficient foragers and/or to have higher reproductive success than generalist individuals, but interspecific reproductive consequences of the degree of diet specialisation in vertebrate predators have remained unstudied. Eurasian pygmy owls (hereafter POs) have less vole‐specialised diets than Tengmalm's owls (TOs), both of which mainly subsist on temporally fluctuating food resources (voles). To test whether the specialist TO is more limited by the main prey abundance than the generalist PO, we studied breeding densities and reproductive traits of co‐existing POs and TOs in central‐western Finland during 2002‐2019. Breeding densities of POs increased with augmenting densities of voles in the previous autumn, whereas breeding densities of TOs increased with higher vole densities in both the previous autumn and the current spring. In years of vole scarcity, PO females started egg‐laying earlier than TOs, whereas in years of vole abundance TO females laid eggs substantially earlier than PO females. The yearly mean clutch size and number of fledglings produced of both POs and TOs increased with abundance of voles in the current spring. POs laid large clutches and produced large broods in years of both high and low vole abundance, whereas TOs were able to do so only in years of high vole abundance. POs were able to raise on average 73% of the eggs to fledglings whereas TOs only 44%. The generalist foraging strategy of POs including flexible switching from main prey to alternative prey (small birds) appeared to be more productive than the strictly vole‐specialized foraging strategy of TOs. In contrast to earlier studies at the individual‐level, specialist predators at the species level (in this case TOs) appear to be less effective than generalists (POs), but diet specialisation was particularly costly under conditions when scarcity of main foods limited offspring production. This article is protected by copyright. All rights reserved.
Article
Variation in prey availability can cause changes in species interactions among marine predators. Foraging theory predicts that niche breadth will expand when resources become limited, possibly leading to higher niche overlap among sympatric species; however, a species’ niche can become constrained by interactions with other similar species, resulting in an inability to shift niche breadth or position. In coastal Newfoundland, Capelin Mallotus villosus is the main forage fish species and its availability (i.e. biomass) during the summer has varied considerably in recent years, following a population collapse in the 1990s. During the summer, non‐breeding Great and Sooty Shearwaters Ardenna gravis and A. grisea migrate and aggregate at annually persistent Capelin spawning sites. We used stable isotope ratios (δ13C, δ15N) of blood components (plasma, red blood cell) to investigate variation in isotopic niche breadth (95% prediction ellipse areas) and overlap of the two shearwater species during 2014, 2015 and 2016. Capelin availability varied among years, illustrated by lower peak biomass in 2015 (0.126 g/m2) and 2016 (0.027 g/m2) relative to 2014 (0.254 g/m2). The isotopic niche breadth (plasma) of both shearwater species expanded similarly from 2014 (0.65‐0.66 ‰2) to 2015 (2.22‐2.57 ‰2), and 2016 (1.15‐1.42 ‰2), suggesting the incorporation of alternative prey types into their diet during years of lower prey availability. Isotopic niche overlap between Great and Sooty Shearwaters remained high across years (44‐63%), however, providing little evidence for dietary niche partitioning during years of lower prey availability. Findings suggest that both shearwaters are flexible foragers and can modify their diet during the non‐breeding season to accommodate fluctuations in prey availability.
Article
Ecological communities are reorganizing in response to warming temperatures. For continuous ocean habitats this reorganization is characterized by large-scale species redistribution, but for tropical discontinuous habitats such as coral reefs, spatial isolation coupled with strong habitat dependence of fish species imply that turnover and local extinctions are more significant mechanisms. In these systems, transient marine heatwaves are causing coral bleaching and profoundly altering habitat structure, yet despite severe bleaching events becoming more frequent and projections indicating annual severe bleaching by the 2050s at most reefs, long-term effects on the diversity and structure of fish assemblages remain unclear. Using a 23-year time series spanning a thermal stress event, we describe and model structural changes and recovery trajectories of fish communities after mass bleaching. Communities changed fundamentally, with the new emergent communities dominated by herbivores and persisting for >15 years, a period exceeding realized and projected intervals between thermal stress events on coral reefs. Reefs which shifted to macroalgal states had the lowest species richness and highest compositional dissimilarity, whereas reefs where live coral recovered exceeded prebleaching fish richness, but remained dissimilar to prebleaching compositions. Given realized and projected frequencies of bleaching events, our results show that fish communities historically associated with coral reefs will not re-establish, requiring substantial adaptation by managers and resource users.
Article
Competition often occurs between two or more sympatric species that use similar ecological niches. During competition, a superior species may exclude the competitor from parts of its fundamental niche or make it go extinct. Determining the potential competition between two sympatric species including an endangered one has important implications for conservation management. We evaluated potential food competition between the wild boar and the giant panda in a key national nature reserve established primarily for the giant panda protection. We monitored foraging plots for 9 years, conducted food macronutrient analysis, and combined our analysis with long-term population monitoring results for two species. The wild boar population increased dramatically in the past 18 years, benefiting from conservation policies of the Chinese government, whereas the giant panda population decreased. We found evidence for competition for bamboo shoots, an important seasonally limiting resource. The wild boar had a higher utilization rate at foraging plots than giant panda, which also avoided plots used by wild boar. This study indicates key seasonal food competition may exist between wild boar and giant panda. This competition for a key food resource may have negative impacts on giant panda populations, particularly under the substantial increase of the wild boar, yet this possibility has not figured prominently in conservation planning and policy for panda reserves. We suggest long-term monitoring of this competitive relationship across reserves to determine when and where management intervention is needed. And, we might need more flexible policies instead of the current “one size fits all” one.
Article
Diet of the Tristan spiny lobster Jasus paulensis was examined using gut content and Stable Isotope Analyses (SIA) to assess whether diets differed among three islands in the Tristan da Cunha archipelago (Inaccessible, Nightingale and Tristan islands), and between small and large lobsters at two depth intervals. Gut fullness was significantly less at Nightingale Island, suggesting overall less food there. Diet differed significantly among all islands, depths and sizes, although multidimensional scaling (MDS) and constrained canonical analysis of principle coordinates (CAP) plots showed considerable overlap and variability in diet. Lobster diet from Tristan Island showed a greater within-island similarity and was significantly less diverse, suggesting a more im- poverished reef and narrower feeding niche, while dietary differences between size and depth reflected prey availability. Carbon and nitrogen stable isotope signatures differed among the islands, and carbon signatures between depths. Jasus paulensis appeared to be an opportunistic omnivore, with diet reflecting impoverished reef habitats. In addition, our data showed no evidence of soya remnants in the gut contents or tissue signatures of lobsters at Nightingale Island, following a soya spill there four years previously. However, gut fullness was less at Nightingale. This may have increased the attractiveness of baited traps, possibly explaining an observed rise in CPUE after the spill.
Book
This expanded and fully updated Second Edition of the most comprehensive and successful book on lobsters, comprises contributions from many of the world's experts, each providing core information for all those working in lobster biology, fisheries research and management and lobster aquaculture. Under the editorship of Bruce Phillips, the Second Edition of Lobsters: Biology, Management, Fisheries and Aquaculture delivers exhaustive coverage of these fascinating creatures, stretching from growth and development to management and conservation. A number of chapters from the First Edition covering Growth, Reproduction, Diseases, Behaviour, Nutrition, Larval and Post-Larval Ecology and Juvenile and Adult Ecology have been replaced by new chapters including Lobsters in Ecosystems, Genetics, Translocation, Climate Change, Ecolabelling of Lobsters, Casitas and Other Artificial Shelters, Systems to maximise Economic Benefits.. These new chapters reflect changes that are occurring in lobster management and new research developments brought on by social, climatic and economic changes. As well as information from new research output, information in each chapter is also included on individual commercial Genera, including aspects of Species and distribution, Predators and diseases, Ecology and behaviour, Aquaculture and enhancement, Harvest of wild populations and their regulations, Management and conservation. The chapter on slipper lobsters has also been expanded to include Thenus and Ibacus species which are now subject to commercial fisheries. The changes that have occurred in some lobster fisheries, the new management arrangements in place, the status of stocks and the current economic and social situation of each fishery have also been covered and discussed in great detail. Fisheries scientists, fisheries managers aquaculture personnel, aquatic and invertebrate biologists, physiologists, ecologists, marine biologists and environmental biologists will all find Lobsters Second Edition to be a vital source of reference. Libraries in all universities and research establishments where biological and life sciences and fisheries and aquaculture are studied and taught will find it an extremely valuable addition to their shelves.
Article
This study examined the trophic ecology of three sympatric tropical tuna species (bigeye BET, skipjack SKJ, and yellowfin YFT) sampled in the Western Indian Ocean throughout 2013. Specifically we explored inter-specific resource partitioning and ontogenetic variability using neutral fatty acids and stable isotope analysis of liver and muscle from small (⩽100 cm fork length, FL) and large (>100 cm FL) tuna collected in mixed schools at the surface by purse-seine. Both biochemical tracers were used to calculate trophic niche indices that collectively revealed high potential for resource overlap, especially among small tuna. Resource overlap appeared strongest between BET and YFT, with SKJ tissues having high carbon isotope (δ13C) values (-17±0.3‰), lower nitrogen isotope (δ15N) values (11.4±0.6‰), and higher relative proportion of poly-unsaturated fatty acids (PUFA) than the two other species, indicating a different diet. Size was found to be a strong predictor for most biochemical tracers in the three species with δ13C, δ15N and total lipid content in the liver. In the larger species (YFT and BET), proportions of mono-unsaturated fatty acids typically increased with size, while quantities of PUFA decreased. In addition to ontogenetic variability, trophic markers were shown to vary between sampling area and season: higher lipid reserves and δ15N values, and lower δ13C values occurred during monsoon periods around Seychelles than in the Mozambique Channel (parted from about 1500 km). Our multi-tracer approach reveals the magnitude of potential competitive interactions in mixed tropical tuna schools at both small and large sizes and demonstrates that ontogenetic niche differentiation acts as a major factor of coexistence in tropical tuna.
Article
In temperate habitats, predation by lobsters creates trophic cascades that reverberate through benthic communities. However, the influence of lobsters on tropical benthic communities is thought to be minimal due to higher prey diversity and the mobility and broad diet of lobsters. We hypothesized that this would not be the case for the spotted spiny lobster (Panulirus guttatus Latreille, 1804), an obligate, philopatric dweller of Caribbean coral reefs. Our study took place in the Florida Keys (USA), where we examined the gut contents of wild lobsters, conducted laboratory experiments on lobster prey selection and foraging effectiveness in rubble, and manipulated lobster density on isolated patch reefs to examine the effects of lobster predation on macroinvertebrate prey over a 3-yr period. We found P. guttatus to be a generalist carnivore that consumed a suite of macroinvertebrates, including important reef herbivores (e.g., herbivorous crabs, gastropods, and urchins) that comprised >60% of its diet. Higher densities of P. guttatus exerted strong top-down control over the abundance and composition of macroinvertebrate prey in rubble substrates on patch reefs, but not prey living in substrates dominated by macroalgae. Lobster foraging success in rubble also depended on rubble size; lobsters extracted prey from and overturned rubble more easily when rubble was smaller. The abundance and high site fidelity of predatory P. guttatus appears to provide the necessary conditions for top-down control of prey in coral reef rubble zones, an effect similar to the powerful influence of lobster predation observed in temperate ecosystems. © 2016 Rosenstiel School of Marine and Atmospheric Science of the University of Miami.
Article
This study investigated the influence of the spatial arrangement of habitat patches on the diet and nutrition of a common reef-associated generalist consumer, the western rock lobster Panulirus cygnus. Stable isotopes (C-13/C-12 and N-15/N-14) and gut contents were used to assess diet and nutrition of lobsters collected from 8 shallow patch-reef sites on the lower west coast of Australia in April and October 2005. A distance-based linear model indicated that the predominant benthic habitat surrounding a reef (seagrass or macroalgae/sand-dominated) was an important source of variation in diet and nutrition, explaining significant (p < 0.01) variation in isotope signatures and gut contents of 52.7 and 7.0%, respectively. Mobile invertebrates, sessile filter feeders, coralline algae and seagrass were consumed by lobsters from all sites, but sessile filter feeders (sponges and colonial ascidians) were consumed in significantly greater volumes (p < 0.05) at macroalgae/sand-dominated sites (21.16 +/- 3.0%) than at seagrass-dominated sites (<= 6.1 +/- 1.08%). A modified mass balance mixing model (IsoSource), which factored in C:N ratios of food sources and lobster-specific delta C-13 and delta N-15 discrimination values, was used to determine the contribution of food sources to lobster nutrition. Articulated coralline red algae were an important source, especially from sites dominated by macroalgae and sand contributing 22-72% to nutrition. Bait potentially contributes up to similar to 30% of lobster muscle nutrition and therefore may also play an important nutritional role for lobsters in areas where lobster potting occurs. Macroalgae, rather than seagrass, appears the most likely autochthonous energy source driving P. cygnus production in shallow coastal waters; however, seagrass plays an important role as habitat for lobster prey.
Article
On-growing of wild-caught juvenile spiny (Palinuridae) lobsters to market size is an emerging aquaculture industry in Asia, Oceania and Central America but most notably in Vietnam where a US$90 million per annum industry flourishes. The sustainability of the supply of wild juveniles is an ever present threat to industry expansion, which ultimately may be overcome through successful life cycle closure. However, another and perhaps more imminent impediment is the present reliance on fresh fishery by-catch as a source of food for lobster culture. The decreasing availability and increasing cost of the by-catch, together with the downstream environmental impacts caused by this type of feeding, has focused attention on the need for more sustainable and environmentally-friendly pelleted feeds. Efforts to develop palatable and high performance pelleted dry feeds for spiny lobster grow-out have not met with a lot of success until recently. This paper reviews the progress that has been made and identifies where further research effort is needed.
Article
Stable isotope ratios provide clues about the origins and transformations of organic matter. A few key reactions control the isotopic composition of most organic matter. Isotopic variations introduced by these reactions are often passed on with little change so that isotopic measurements can indicate natural pathways and flows “downstream” from these key reactions. When chemical and metabolic processes scramble the information content of molecules, isotopic compositions are often preserved. This realization has prompted increasing use of stable isotope analyses as a tool for understanding complex ecological processes.
Article
1. Understanding the processes by which species sort themselves into communities remains a central puzzle for attempts to maintain biodiversity. It remains unclear whether any single assembly process is generally dominant or whether the influence of contrasting processes varies in a predictable way relative to biotic and abiotic gradients. Abundance-weighted niche overlap between species provides a powerful means of contrasting two major assembly processes – niche complementarity and environmental filtering.
Article
FA signature analysis has the potential to be a very powerful technique in both qualitative and quantitative investigations in many areas of ecology, particularly in trophic studies. In this review, we have attempted to provide both general guidelines, as well as detailed procedures, to follow for accurate analysis while avoiding some common pitfalls. The underlying message is, in all cases, to use common sense and prudence in sample collection, preparation, analysis, and interpretation. Some understanding of the protocols described here will allow biologists to make logical decisions regarding the course to follow in collecting and analyzing samples and in interpreting resulting data.
Article
The abundance and availability of food are critical determininants of reproductive success and population dynamics of marine top predators. However, recent work has indicated that the quality of the food may also be critically important for some marine predators. The ‘junkfood hypothesis’ was originally suggested as a potential explanation for a dramatic population decline of Stellers sea lions Eumetopias jubatus in the Gulf of Alaska. According to the hypothesis, a dietary switch to prey of low energy content led to detrimental effects on the population of sea lions. A number of observations indicate that the hypothesis is relevant for several population parameters. Recent work on piscivorous seabirds has provided substantial evidence indicating the relevance of this hypothesis in food webs in e.g. the North Pacific, the North Sea and the Baltic Sea. The emergence of ‘junk-food’ in these systems may be coupled to large scale changes in climatological and oceanographic forcing, although predation, fishing and competition provide additional plausible hypotheses. It may be possible to predict which kinds of animals will be particularly sensitive to food quality; these seem to be species with limited ability to carry food loads, with energetically-expensive foraging behaviour, and with digestive anatomy evolved to minimize mass at the cost of digestive efficiency. This review suggests that the junk-food hypothesis is a highly relevant factor in relation to sustaining ecosystem resilience, and is an important consideration in ecosystem management. Sustaining healthy populations of marine top-predators requires an understanding of the role of food quality, in addition to food abundance and availability.
Article
Coral reef ecosystems are among the most biologically diverse ecosystems on the planet. In addition to their value in terms of biodiversity, coral reefs provide food and resources for over 500million people. Despite their importance, coral reefs are declining at a rapid rate (1–2% per year) as a result of a range of local (e.g., overexploitation of fisheries, declining water quality) and global (e.g., global warming and ocean acidification) drivers. Extensive experimental and field evidence suggests that atmospheric carbon dioxide concentrations of 450ppm will lead to the loss of coral-dominated reef systems, with the prospect that dangerous levels of atmospheric carbon dioxide for coral reefs were exceeded in 1979 when mass coral bleaching was reported for the first time. The exact response of coral reefs remains uncertain although it is highly unlikely that coral-dominated reef systems will be present in future oceans at the current rate of warming and acidification of the world’s tropical oceans. The loss of these important coastal ecosystems will diminish the resources available to hundreds of millions of people along tropical coastlines. Understanding the impacts on people and industry is an imperative if we are to devise effective systems by which tropical coastal communities are to adapt to rapidly changing tropical coastal environments. Our current understanding of these important issues, however, is in a relatively undeveloped state and must be a priority of future research. KeywordsCoral reef–Climate change–Ocean acidification–Calcification–Marine biodiversity–Coastal communities–Declining resources–Mass coral bleaching
FAO species catalogue Vol. 13. Marine lobsters of the world an annotated and illustrated catalogue of species of interest to fisheries known to date
  • Holthuis
Marine lobsters of the world an annotated and illustrated catalogue of species of interest to fisheries known to date
  • L B Holthuis
Holthuis, L.B., 1991. FAO species catalogue Vol. 13. Marine lobsters of the world an annotated and illustrated catalogue of species of interest to fisheries known to date. FAO Fish Synopsis 13, 1-4. http://www.fao.org/3/t0411e/t0411e00.htm.
Lobster survey report
Seychelles Fishing Authority, 2018. Lobster survey report 2018. https://www.oceandocs. org/bitstream/handle/1834/15432/Tech.082.pdf.