Longer and less overlapping food webs in anthropogenically disturbed marine ecosystems: confirmations from the past

The human exploitation of marine resources is characterised by the preferential removal of the largest species. Although this is expected to modify the structure of food webs, we have a relatively poor understanding of the potential consequences of such alteration. Here, we take advantage of a collection of ancient consumer tissues, using stable isotope analysis and SIBER to assess changes in the structure of coastal marine food webs in the South-western Atlantic through the second half of the Holocene as a result of the sequential exploitation of marine resources by hunter-gatherers, western sealers and modern fishermen. Samples were collected from shell middens and museums. Shells of both modern and archaeological intertidal herbivorous molluscs were used to reconstruct changes in the stable isotopic baseline, while modern and archaeological bones of the South American sea lion Otaria flavescens, South American fur seal Arctocephalus australis and Magellanic penguin Spheniscus magellanicus were used to analyse changes in the structure of the community of top predators. We found that ancient food webs were shorter, more redundant and more overlapping than current ones, both in northern-central Patagonia and southern Patagonia. These surprising results may be best explained by the huge impact of western sealing on pinnipeds during the fur trade period, rather than the impact of fishing on fish populations. As a consequence, the populations of pinnipeds at the end of the sealing period were likely well below the ecosystem's carrying capacity, which resulted in a release of intraspecific competition and a shift towards larger and higher trophic level prey. This in turn led to longer and less overlapping food webs

Cambios en la posición trófica del lobo común sudamericano (Otaria flavescens) en respuesta a la explotación masiva de mamíferos marinos y pesca industrial

[spa] Los depredadores marinos pueden cambiar su dieta a través del tiempo como consecuencia de cambios antropogénicos y naturales, por lo que un punto de referencia histórico aporta información básica y necesaria para comprender el papel ecológico que desempeñan estos individuos dentro del ecosistema que habitan. En las costas del Atlántico sudoccidental los registros zooarqueologicos e históricos revelan una importante explotación de los lobos marinos sudamericanos por parte de los colonizadores europeos y en menor grado por parte de los aborígenes cazadores recolectores, sin embargo, poco se sabe sobre la influencia de estas explotaciones sobre la dieta de esta especie. Debido a que los lobos marinos sudamericanos se caracterizan por tener un amplio nicho trófico, el determinante principal de la composición de sus dietas es la competencia intraespecifica, por lo que se espera que estos animales muestren un cambio en la posición trófica asociado a la caza indiscriminada por parte de los colonizadores europeos, y un impacto menor sobre sus poblaciones y dietas como resultado de la caza aborigen. En esta tesis doctoral se realizaron análisis de isótopos estables de carbono y nitrógeno en muestras zooarqueológicas y modernas, provenientes del centro-norte y sur de Patagonia Argentina con el objetivo de reconstruir la dieta de los lobos marinos sudamericanos desde el Holoceno tardío al presente. Los resultados revelan un marcado aumento del nivel trófico durante el siglo XX, el cual podría estar relacionado con una disminución del tamaño poblacional del lobo común sudamericano, como consecuencia de la explotación comercial, y una reducción de la competencia intraespecífica. Al contrario, tanto en Patagonia norte-centro como en Patagonia sur, las poblaciones de lobos marinos sudamericanos mostraron una estabilidad en la dieta durante varios milenios de explotación aborigen. Asimismo, no se observaron cambios significativos durante las últimas tres décadas en las razones isotópicas del hueso de machos jóvenes y adultos de lobo marino sudamericano procedentes del sur de Brasil a pesar de un dramático incremento en el desarrollo de la pesquería demersal, lo cual sugiere que la población regional se encuentra muy por debajo de la capacidad de carga. Estos resultados confirman la importancia de los análisis retrospectivos de las razones isotópicos para inferir cambios en la dieta de los depredadores oportunistas, y para identificar la transición ecológica entre ecosistemas prístinos y modificados antropogénicamente.[eng] Marine predators may undergo remarkable dietary changes through time as a result of both anthropogenic and natural changes in the environment, and hence, a historical point of reference provides the necessary basic information to understand the ecological function of individuals in the ecosystem. In the south-west Atlantic coasts, zooarchaeological and historical records revealed a significant exploitation of South American sea lions by European colonizers and to a lesser extent by aboriginal hunter-gatherers, however, little is known about the influence of these exploitations on the diet of sea lions. Because South American sea lions have been reported as broad spectrum, the intraspecific competition plays an important role in the composition of their diets. It is therefore expected a change in the trophic position of these animals associated with the indiscriminate hunting by Western sealing, and less impact on their populations and diets as a result of aboriginal exploitation. Stable isotope ratios of carbon and nitrogen in archaeological and modern samples from northern-central and southern Patagonia, Argentina have been used in this doctoral thesis to reconstruct the dietary changes of the South American sea lion from the late Holocene to the present in the southwestern Atlantic. Results show a marked increase in trophic level during the twentieth century which might be related to the smaller population size resulting from modern sealing and the resulting reduced intraspecific competition. On the contrary, populations of South American sea lions from both in north-central Patagonia and southern Patagonia showed a stability in the diet for several millennia of aboriginal exploitation. Furthermore, no major changes were detected in the diet of male South American sea lions during the past three decades from southern Brazil despite a dramatic increase in the development of demersal fisheries, suggesting that population levels may be below of their optimal carrying capacity Results confirmed the importance of retrospective analysis of the stable isotope ratios to infer changes in the diet of opportunistic predators, and to identify the ecological transition between pristine ecosystems and anthropogenically modified

Cambios en la posición trófica del lobo común sudamericano (Otaria flavescens) en respuesta a la explotación masiva de mamíferos marinos y pesca industrial

Los depredadores marinos pueden cambiar su dieta a través del tiempo como consecuencia de cambios antropogénicos y naturales, por lo que un punto de referencia histórico aporta información básica y necesaria para comprender el papel ecológico que desempeñan estos individuos dentro del ecosistema que habitan. En las costas del Atlántico sudoccidental los registros zooarqueologicos e históricos revelan una importante explotación de los lobos marinos sudamericanos por parte de los colonizadores europeos y en menor grado por parte de los aborígenes cazadores recolectores, sin embargo, poco se sabe sobre la influencia de estas explotaciones sobre la dieta de esta especie. Debido a que los lobos marinos sudamericanos se caracterizan por tener un amplio nicho trófico, el determinante principal de la composición de sus dietas es la competencia intraespecifica, por lo que se espera que estos animales muestren un cambio en la posición trófica asociado a la caza indiscriminada por parte de los colonizadores europeos, y un impacto menor sobre sus poblaciones y dietas como resultado de la caza aborigen. En esta tesis doctoral se realizaron análisis de isótopos estables de carbono y nitrógeno en muestras zooarqueológicas y modernas, provenientes del centro-norte y sur de Patagonia Argentina con el objetivo de reconstruir la dieta de los lobos marinos sudamericanos desde el Holoceno tardío al presente. Los resultados revelan un marcado aumento del nivel trófico durante el siglo XX, el cual podría estar relacionado con una disminución del tamaño poblacional del lobo común sudamericano, como consecuencia de la explotación comercial, y una reducción de la competencia intraespecífica. Al contrario, tanto en Patagonia norte-centro como en Patagonia sur, las poblaciones de lobos marinos sudamericanos mostraron una estabilidad en la dieta durante varios milenios de explotación aborigen. Asimismo, no se observaron cambios significativos durante las últimas tres décadas en las razones isotópicas del hueso de machos jóvenes y adultos de lobo marino sudamericano procedentes del sur de Brasil a pesar de un dramático incremento en el desarrollo de la pesquería demersal, lo cual sugiere que la población regional se encuentra muy por debajo de la capacidad de carga. Estos resultados confirman la importancia de los análisis retrospectivos de las razones isotópicos para inferir cambios en la dieta de los depredadores oportunistas, y para identificar la transición ecológica entre ecosistemas prístinos y modificados antropogénicamente.Marine predators may undergo remarkable dietary changes through time as a result of both anthropogenic and natural changes in the environment, and hence, a historical point of reference provides the necessary basic information to understand the ecological function of individuals in the ecosystem. In the south-west Atlantic coasts, zooarchaeological and historical records revealed a significant exploitation of South American sea lions by European colonizers and to a lesser extent by aboriginal hunter-gatherers, however, little is known about the influence of these exploitations on the diet of sea lions. Because South American sea lions have been reported as broad spectrum, the intraspecific competition plays an important role in the composition of their diets. It is therefore expected a change in the trophic position of these animals associated with the indiscriminate hunting by Western sealing, and less impact on their populations and diets as a result of aboriginal exploitation. Stable isotope ratios of carbon and nitrogen in archaeological and modern samples from northern-central and southern Patagonia, Argentina have been used in this doctoral thesis to reconstruct the dietary changes of the South American sea lion from the late Holocene to the present in the southwestern Atlantic. Results show a marked increase in trophic level during the twentieth century which might be related to the smaller population size resulting from modern sealing and the resulting reduced intraspecific competition. On the contrary, populations of South American sea lions from both in north-central Patagonia and southern Patagonia showed a stability in the diet for several millennia of aboriginal exploitation. Furthermore, no major changes were detected in the diet of male South American sea lions during the past three decades from southern Brazil despite a dramatic increase in the development of demersal fisheries, suggesting that population levels may be below of their optimal carrying capacity Results confirmed the importance of retrospective analysis of the stable isotope ratios to infer changes in the diet of opportunistic predators, and to identify the ecological transition between pristine ecosystems and anthropogenically modified

Cambios en la posición trófica del lobo común sudamericano (Otaria flavescens) en respuesta a la explotación masiva de mamíferos marinos y pesca industrial

Los depredadores marinos pueden cambiar su dieta a través del tiempo como consecuencia de cambios antropogénicos y naturales, por lo que un punto de referencia histórico aporta información básica y necesaria para comprender el papel ecológico que desempeñan estos individuos dentro del ecosistema que habitan. En las costas del Atlántico sudoccidental los registros zooarqueologicos e históricos revelan una importante explotación de los lobos marinos sudamericanos por parte de los colonizadores europeos y en menor grado por parte de los aborígenes cazadores recolectores, sin embargo, poco se sabe sobre la influencia de estas explotaciones sobre la dieta de esta especie. Debido a que los lobos marinos sudamericanos se caracterizan por tener un amplio nicho trófico, el determinante principal de la composición de sus dietas es la competencia intraespecifica, por lo que se espera que estos animales muestren un cambio en la posición trófica asociado a la caza indiscriminada por parte de los colonizadores europeos, y un impacto menor sobre sus poblaciones y dietas como resultado de la caza aborigen. En esta tesis doctoral se realizaron análisis de isótopos estables de carbono y nitrógeno en muestras zooarqueológicas y modernas, provenientes del centro-norte y sur de Patagonia Argentina con el objetivo de reconstruir la dieta de los lobos marinos sudamericanos desde el Holoceno tardío al presente. Los resultados revelan un marcado aumento del nivel trófico durante el siglo XX, el cual podría estar relacionado con una disminución del tamaño poblacional del lobo común sudamericano, como consecuencia de la explotación comercial, y una reducción de la competencia intraespecífica. Al contrario, tanto en Patagonia norte-centro como en Patagonia sur, las poblaciones de lobos marinos sudamericanos mostraron una estabilidad en la dieta durante varios milenios de explotación aborigen. Asimismo, no se observaron cambios significativos durante las últimas tres décadas en las razones isotópicas del hueso de machos jóvenes y adultos de lobo marino sudamericano procedentes del sur de Brasil a pesar de un dramático incremento en el desarrollo de la pesquería demersal, lo cual sugiere que la población regional se encuentra muy por debajo de la capacidad de carga. Estos resultados confirman la importancia de los análisis retrospectivos de las razones isotópicos para inferir cambios en la dieta de los depredadores oportunistas, y para identificar la transición ecológica entre ecosistemas prístinos y modificados antropogénicamente.Marine predators may undergo remarkable dietary changes through time as a result of both anthropogenic and natural changes in the environment, and hence, a historical point of reference provides the necessary basic information to understand the ecological function of individuals in the ecosystem. In the south-west Atlantic coasts, zooarchaeological and historical records revealed a significant exploitation of South American sea lions by European colonizers and to a lesser extent by aboriginal hunter-gatherers, however, little is known about the influence of these exploitations on the diet of sea lions. Because South American sea lions have been reported as broad spectrum, the intraspecific competition plays an important role in the composition of their diets. It is therefore expected a change in the trophic position of these animals associated with the indiscriminate hunting by Western sealing, and less impact on their populations and diets as a result of aboriginal exploitation. Stable isotope ratios of carbon and nitrogen in archaeological and modern samples from northern-central and southern Patagonia, Argentina have been used in this doctoral thesis to reconstruct the dietary changes of the South American sea lion from the late Holocene to the present in the southwestern Atlantic. Results show a marked increase in trophic level during the twentieth century which might be related to the smaller population size resulting from modern sealing and the resulting reduced intraspecific competition. On the contrary, populations of South American sea lions from both in north-central Patagonia and southern Patagonia showed a stability in the diet for several millennia of aboriginal exploitation. Furthermore, no major changes were detected in the diet of male South American sea lions during the past three decades from southern Brazil despite a dramatic increase in the development of demersal fisheries, suggesting that population levels may be below of their optimal carrying capacity Results confirmed the importance of retrospective analysis of the stable isotope ratios to infer changes in the diet of opportunistic predators, and to identify the ecological transition between pristine ecosystems and anthropogenically modified

Ontogenetic dietary changes in male South American fur seals Arctocephalus australis in Patagonia

This study assessed ontogenetic dietary changes in male South American fur sealsArctocephalus australis in northern and central Patagonia (Argentina) using stable isotope ratios (δ15N and δ13C) in vibrissae and bones. Sucking pups were characterised by higher δ15N values and lower δ13C values than older specimens. Weaning was associated with a marked drop of δ15N values, both in bone and vibrissae. Such a drop was inconsistent with the consumption of local prey and may reveal movement to distant foraging grounds or physiological changes associatedwith either fasting or rapid growth. Stable isotope ratios indicated that juveniles fed more pelagically than subadults and adults, but that there were no major differences between the 2 latter age categories. As subadults and adults are rather similar in body mass and are much larger than juveniles, body mass may play a role in the ontogenetic dietary changes reported. Nevertheless, demersal benthic prey were always scarce in the diet of male fur seals, which relied primarily onArgentine shortfin squid and small pelagic fish throughout life, though adults also consumed large amounts of decapod crustaceans available at shallow depths. Vibrissae did not reveal regular oscillations of δ15N or δ13C, except in 1 individual. Thus, male fur seals from northern and central Patagonia do not appear to migrate regularly between isotopically distinct areas, although nomadic displacements cannot be ruled out.Fil: Vales, Damián Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Cardona, Luis. Universidad de Barcelona. Facultad de Biología. Departamento de Biología Animal; EspañaFil: Garcia, Nestor Anibal. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Zenteno, Lisette. Universidad de Barcelona. Facultad de Biología. Departamento de Biología Animal; EspañaFil: Crespo, Enrique Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentin

Ontogenetic dietary changes in male South American fur seals Arctocephalus australis in northern and central Patagonia, Argentina.

This study assessed ontogenetic dietary changes in male South American fur seals Arctocephalus australis in northern and central Patagonia (Argentina) using stable isotope ratios (δ15 N and δ13 C) in vibrissae and bones. Sucking pups were characterised by higher δ15 N values and lower δ13 C values than older specimens. Weaning was associated with a marked drop of δ15 N values, both in bone and vibrissae. Such a drop was inconsistent with the consumption of local prey and may reveal movement to distant foraging grounds or physiological changes associated with either fasting or rapid growth. Stable isotope ratios indicated that juveniles fed more pelagically than subadults and adults, but that there were no major differences between the 2 latter age categories. As subadults and adults are rather similar in body mass and are much larger than juveniles, body mass may play a role in the ontogenetic dietary changes reported. Nevertheless, demersal benthic prey were always scarce in the diet of male fur seals, which relied primarily on Argentine shortfin squid and small pelagic fish throughout life, though adults also consumed large amounts of decapod crustaceans available at shallow depths. Vibrissae did not reveal regular oscillations of δ15 N or δ13 C, except in 1 individual. Thus, male fur seals from northern and central Patagonia do not appear to migrate regularly between isotopically distinct areas, although nomadic displacements cannot be ruled out

Microplastic Particles’ Effects on Aquatic Organisms and Their Role as Transporters of Organic Pollutants

Microplastic (MP) contamination is considered a growing problem in terms of its production and observed impacts on aquatic organisms. In this study, we investigated the adverse effects that could occur from pure polyethylene (PE) MPs and PE contaminated with phenanthrene (Phe) and chlorpyrifos (CPF) in D. magna and podocopid ostracods. The organisms were exposed to different sizes (1–5, 27–32, 45–53, and 212–250 μm) and concentrations of MPs (0, 16, 160, 1600, 16,000 particles/mL) using a static and dynamic model of exposition. The results indicate that both daphnia and ostracods can ingest MPs, and the effect observed in most cases is directly proportional to the concentration of MPs. Exposure to pure MP did not affect the organisms. However, at 21 days, they induced a significant decrease (p D. magna juveniles with increasing size, while in ostracods, mortality increased with decreasing particle size. The effect of the MPs in crustaceans would depend on the concentration, exposure time, size of the organisms, and size of the MPs. It is also shown that the toxicity of PE increases when these particles are associated with a contaminant, which would indicate its role as a transporter of organic contaminants

Temporal variability in stable isotope ratios of C and N in the vibrissa of captive and wild adult South American sea lions Otaria byronia : More than just diet shifts

We analyzed the d13C and d15N values in the vibrissae of captive adult breeding South American sea lions (Otaria byronia) fed at a constant diet and then used thisinformation to analyze the change in stable isotope values along the vibrissae from wild individuals. The overall diet-to-vibrissa discrimination factor of the captive animals was 3.0& 0.1& for d13C and 3.6& 0.1& for d15N, but the stable isotope ratios fluctuated periodically despite constant diet. The d13C and d15N valuesof the captive male declined at the end of the breeding season, whereas the d13C values of the female increased during the central part of pregnancy and the d15N valuespeaked during lactation. The d13C and d15N values of adult wild specimens alsofluctuated periodically and vibrissae growth rate (0.15 mm/d in both sexes) was slightly lower than in captivity (0.17 mm/d), assuming an annual periodicity foroscillations. Similarities in the amplitude of the cycles of captive and wild males suggested that fasting was probably the main source of periodic variability in the d15N of wild males, whereas pregnancy and lactation were probably the main source of periodic variability for the d13C of wild females.Fil: Cardona, Luis. Universidad de Barcelona; EspañaFil: Vales, Damián Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Aguilar, Alex. Universidad de Barcelona; EspañaFil: Crespo, Enrique Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Zenteno, Lisette. Universidad de Barcelona; Españ

Ontogenetic dietary changes in male South American fur seals Arctocephalus australis in northern and central Patagonia, Argentina.

This study assessed ontogenetic dietary changes in male South American fur seals Arctocephalus australis in northern and central Patagonia (Argentina) using stable isotope ratios (δ15 N and δ13 C) in vibrissae and bones. Sucking pups were characterised by higher δ15 N values and lower δ13 C values than older specimens. Weaning was associated with a marked drop of δ15 N values, both in bone and vibrissae. Such a drop was inconsistent with the consumption of local prey and may reveal movement to distant foraging grounds or physiological changes associated with either fasting or rapid growth. Stable isotope ratios indicated that juveniles fed more pelagically than subadults and adults, but that there were no major differences between the 2 latter age categories. As subadults and adults are rather similar in body mass and are much larger than juveniles, body mass may play a role in the ontogenetic dietary changes reported. Nevertheless, demersal benthic prey were always scarce in the diet of male fur seals, which relied primarily on Argentine shortfin squid and small pelagic fish throughout life, though adults also consumed large amounts of decapod crustaceans available at shallow depths. Vibrissae did not reveal regular oscillations of δ15 N or δ13 C, except in 1 individual. Thus, male fur seals from northern and central Patagonia do not appear to migrate regularly between isotopically distinct areas, although nomadic displacements cannot be ruled out

Resource partitioning among air-breathing marine predators: are body size and mouth diameter the major determinants?

Although the body size of consumers may be a determinant factor in structuring food webs, recent evidence indicates that body size may fail to fully explain differences in the resource use patterns of predators in some situations. Here we compared the trophic niche of three sympatric and sexually dimorphic airbreathing marine predators (the South American sea lion, Otaria flavescens, the South American fur seal, Arctocephalus australis, and the Magellanic penguin, Spheniscus magellanicus) in three areas of the Southwestern Atlantic Ocean (R ıo de la Plata and adjoining areas, Northern Patagonia and Southern Patagonia), in order to assess the importance of body size and mouth diameter in determining resource partitioning. Body weight and palate/bill breadth were used to characterize the morphology of each sex and species, whereas the trophic niche was assessed through the use of stable isotope ratios of carbon and nitrogen. The quantitative method Stable Isotope Bayesian Ellipses in R (SIBER) was used to compute the area of the Bayesian ellipses and the overlap of the isotopic niches. The results showed that morphological similarity was significantly correlated with isotopic distance between groups within the d13C– d15N bi-plot space in the R ıo de la Plata area, but not in Northern and Southern Patagonia. Furthermore, resource partitioning between groups changed regionally, and some morphologically distinct groups exhibited a large trophic overlap in certain areas, such as the case of male penguins and male sea lions in Southern Patagonia. Conversely, female sea lions always overlapped with the much larger males of the same species, but never overlapped with the morphologically similar male fur seals. These results indicate that body size and mouth diameter are just two of the factors involved in resource partitioning within the guild of air-breathing predators considered here, and for whom – under certain environmental conditions – other factors are more important than morphology.Fil: Saporiti, Fabiana. Universidad de Barcelona; EspañaFil: Bearhop, Stuart. University Of Exeter; Reino UnidoFil: Vales, Damián Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Silva, Laura. Universidade Federal do Rio Grande do Sul; BrasilFil: Zenteno, Lisette. Universidad de Barcelona; EspañaFil: Tavares, Mauricio. Universidade Federal do Rio Grande do Sul; BrasilFil: Crespo, Enrique Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina. Universidad Nacional de la Patagonia; ArgentinaFil: Cardona, Luis. Universidad de Barcelona; Españ