RESUMO
The use of stable isotopes of carbon (δ13C) and nitrogen (δ15N) from feces and breath offers potential as non-destructive tools to assess diets and nutrition. How stable isotope values derived from breath and feces compare with those from commonly used tissues, such as blood fractions and liver, remains uncertain, including understanding the metabolic routing of dietary nutrients. Here, we measured δ13C and δ15N from feces and δ13C of breath from captive Red-necked Stints (Calidris ruficollis) and 26 species of wild-caught migratory shorebirds (n = 259 individuals) and compared them against isotopic values from blood and feathers. For captive birds fed either cereal- or fish-based diets, differences in δ13C between feces and lipid-free diet were small, - 0.2 ± 0.5 and 0.1 ± 0.3, respectively, and differences in δ15N, - 0.7 ± 0.5 and - 0.5 ± 0.5, respectively. Hence, δ13C and δ15N values from feces can serve as proxies for ingested proteinaceous tissues and non-soluble carbohydrates because isotopic discrimination can be considered negligible. Stable isotope values in plasma and feces were strongly correlated in wild-caught shorebirds, indicating feces can be used to infer assimilated macronutrients. Breath δ13C was 1.6 ± 0.8 to 5.6 ± 1.2 lower than bulk food sources, and breath C derived from lipids was estimated at 47.5% (cereal) to 96.1% (fish), likely underlining the importance of dietary lipids for metabolism. The findings validate the use of stable isotope values of feces and breath in isotopic assays to better understand the dietary needs of shorebirds.
Assuntos
Carbono , Dieta , Animais , Carboidratos , Isótopos de Carbono/metabolismo , Dieta/veterinária , Fezes , Peixes/metabolismo , Isótopos de Nitrogênio/metabolismoRESUMO
This study examines microplastic (MP, 1-5 mm) densities in convergence zones in a coastal sea, the Seto Inland Sea, comparing them to those of non-convergence zones and other areas. Notably, Seto convergence zones exhibit MP densities 40 to 300 times higher than non-convergence zones, with an extraordinary density of 3.7 ± 6.3 pieces m-3, similar to densities found in Tokyo Bay as known a MP hotspot. The predominant polymer found was expanded polystyrene, varying seasonally and peaking in summer. Juvenile fish associated with driftweed in these convergence zones face a risk of long-term MP exposure, potentially up to four months. This large number of MPs found in coastal convergence zones is similar to accumulation zones formed in the gyres of open oceans, with strong implications for detrimental effects on coastal marine life. However, these MPs are autochthonous, and may be manageable through local marine plastic waste management.
Assuntos
Monitoramento Ambiental , Microplásticos , Poluentes Químicos da Água , Microplásticos/análise , Poluentes Químicos da Água/análise , Animais , Peixes , Plásticos/análiseRESUMO
Food webs are comprised of a network of trophic interactions and are essential to elucidating ecosystem processes and functions. However, the presence of unknown, but critical networks hampers understanding of complex and dynamic food webs in nature. Here, we empirically demonstrate a missing link, both critical and variable, by revealing that direct predator-prey relationships between shorebirds and biofilm are widespread and mediated by multiple ecological and evolutionary determinants. Food source mixing models and energy budget estimates indicate that the strength of the missing linkage is dependent on predator traits (body mass and foraging action rate) and the environment that determines food density. Morphological analyses, showing that smaller bodied species possess more developed feeding apparatus to consume biofilm, suggest that the linkage is also phylogenetically dependent and affords a compelling re-interpretation of niche differentiation. We contend that exploring missing links is a necessity for revealing true network structure and dynamics.
Assuntos
Biofilmes , Charadriiformes/fisiologia , Comportamento Alimentar , Cadeia Alimentar , Animais , Bico/anatomia & histologia , Tamanho Corporal , Charadriiformes/classificação , Dieta , Metabolismo Energético , Isótopos/química , Modelos Biológicos , Filogenia , Comportamento Predatório , Língua/anatomia & histologia , Língua/ultraestruturaRESUMO
Chemical compositions of Coscinodiscus wailesii were determined for four samples of natural cells. Results revealed that the cellular Si:N ratio of C. wailesii cell was 2.4:1.0-5.2:1.0. The impacts of C. wailesii on surrounding coastal water were evaluated from hydrographic observations, in which C. wailesii cell density, nutrients concentrations and temperature were monitored from November 2001 to February 2005 in Harima-Nada, the Seto Inland Sea, Japan. In low temperature periods, from October to December, two peaks of C. wailesii cell density were observed and nutrient concentrations were depleted. The draw-down ratio of Si(OH)(4) and DIN (Si(OH)(4):DIN ratio) in the water column were similar to the cellular Si:N ratio of C. wailesii cells, which have high Si contents. In addition the effects of different Si(OH)(4):DIN ratio were determined for in situ bottle incubation experiments. In the culture experiments, picoplankton (0.2-2.0 microm) which consisted of small flagellates became dominant under low Si(OH)(4):DIN ratios. These results suggested that the sizes distribution shifted to small size and the phytoplankton community was changed to small flagellates after the C. wailesii bloom. These changes would influence predators at higher trophic levels in its coastal ecosystem.
Assuntos
Diatomáceas/química , Água do Mar/química , Biodiversidade , Clorofila/análise , Clorofila A , Japão , Oceanos e Mares , Fosfatos/análise , Fitoplâncton/classificação , Densidade Demográfica , Estações do Ano , Ácido Silícico/análise , TemperaturaRESUMO
Small single-celled Chaetoceros sp. are often widely distributed, but frequently overlooked. An estuarine diatom with an extremely high growth potential under optimal conditions was isolated from the Shinkawa-Kasugagawa estuary in the eastern part of the Seto Inland Sea, western Japan. It was identified as Chaetoceros salsugineum based on morphological observations. This strain had a specific growth rate of 0.54 h(-1) at 30°C under 700 µmol · m(-2) · s(-1) (about 30% of natural maximal summer light) with a 14:10 L:D cycle; there was little growth in the dark. However, under continuous light it grew at only 0.35 h(-1) or a daily specific growth rate of 8.4 d(-1) . In addition, cell density, chlorophyll a, and particulate organic carbon concentrations increased by about 1000 times in 24 h at 30°C under 700 µmol · m(-2) · s(-1) with a 14:10 L:D cycle, showing a growth rate of close to 7 d(-1) . This very rapid growth rate may be the result of adaptation to this estuarine environment with high light and temperature. Thus, C. salsugineum can be an important primary producer in this estuary in summer and also an important organism for further physiological and genetic research.