Do Red Knots (Calidris Canutus Islandica) routinely skip Iceland during southward migration?

Subspecies Calidris canutus islandica of the Red Knot breeds on the arctic tundra of northeastern Canada and northern Greenland and winters along the coasts of northwestern Europe. During northward migration, it stops over in either Iceland or northern Norway. It has been assumed that it does the same during southward migration. Using ratios of stable carbon isotopes (δ ¹³ C) in whole blood, blood cells, and plasma, we investigated evidence for a stopover in Iceland en route from the breeding grounds to the Dutch Wadden Sea. With the expected diet (shellfish) and stopover duration at Iceland (12-15 days, maximum 17 days) and the turnover rates of blood cells (15.1 days) and plasma (6.0 days), Red Knots that stopped in Iceland should arrive with a blood (cell) δ ¹³ C midway between a tundra (-24.7[per thousand]) and a marine value (-14.0[per thousand]) and a plasma δ¹³ C approaching the marine value (-15.3[per thousand]). However, many adults arriving at the Wadden Sea had δ¹³ C ratios in blood (cells) and plasma below these levels, and some arrived with clear tundra signals in blood cells, suggesting that they skipped Iceland during southward migration. Surprisingly, available data suggest this also to be true for juveniles during their first southward migration. The δ ¹³ C signature of second-year birds confirmed that they oversummered in the Wadden Sea. Our findings contradict the largely untested idea that juvenile shorebirds make more stopovers than adults as well as the idea that the migration between the Nearctic and Europe is necessarily a two-leg process.

Identifying the African wintering grounds of hybrid flycatchers using a multi-isotope (δ2H, δ13C, δ15N) assignment approach

Migratory routes and wintering grounds can have important fitness consequences, which can lead to divergent selection on populations or taxa differing in their migratory itinerary. Collared (Ficedula albicollis) and pied (F. hypoleuca) flycatchers breeding in Europe and wintering in different sub-Saharan regions have distinct migratory routes on the eastern and western sides of the Sahara desert, respectively. In an earlier paper, we showed that hybrids of the two species did not incur reduced winter survival, which would be expected if their migration strategy had been a mix of the parent species' strategies potentially resulting in an intermediate route crossing the Sahara desert to different wintering grounds. Previously, we compared isotope ratios and found no significant difference in stable-nitrogen isotope ratios (δ15N) in winter-grown feathers between the parental species and hybrids, but stable-carbon isotope ratios (δ13C) in hybrids significantly clustered only with those of pied flycatchers. We followed up on these findings and additionally analyzed the same feathers for stable-hydrogen isotope ratios (δ2H) and conducted spatially explicit multi-isotope assignment analyses. The assignment results overlapped with presumed wintering ranges of the two species, highlighting the efficacy of the method. In contrast to earlier findings, hybrids clustered with both parental species, though most strongly with pied flycatcher.

From food to offspring down : tissue-specific discrimination and turn-over of stable isotopes in herbivorous waterbirds and other avian foraging guilds

Isotopic discrimination and turn-over are fundamental to the application of stable isotope ecology in animals. However, detailed information for specific tissues and species are widely lacking, notably for herbivorous species. We provide details on tissue-specific carbon and nitrogen discrimination and turn-over times from food to blood, feathers, claws, egg tissues and offspring down feathers in four species of herbivorous waterbirds. Source-to-tissue discrimination factors for carbon (δ¹³C) and nitrogen stable isotope ratios (δ¹⁵N) showed little variation across species but varied between tissues. Apparent discrimination factors ranged between −0.5 to 2.5‰ for δ¹³C and 2.8 to 5.2‰ for δ¹⁵N, and were more similar between blood components than between keratinous tissues or egg tissue. Comparing these results with published data from other species we found no effect of foraging guild on discrimination factors for carbon but a significant foraging-guild effect for nitrogen discrimination factors.

Turn-over of δ¹³C in tissues was most rapid in blood plasma, with a half-life of 4.3 d, whereas δ¹³C in blood cells had a half-life of approximately 32 d. Turn-over times for albumen and yolk in laying females were similar to those of blood plasma, at 3.2 and 6.0 d respectively. Within yolk, we found decreasing half-life times of δ¹³C from inner yolk (13.3 d) to outer yolk (3.1 d), related to the temporal pattern of tissue formation.

We found similarities in tissue-specific turn-over times across all avian species studied to date. Yet, while generalities regarding discrimination factors and tissue turn-over times can be made, a large amount of variation remains unexplained.

Paleoreconstruction of estuarine sediments reveal human-induced weakening of coastal carbon sinks

Human activities in coastal areas frequently cause loss of benthic macrophytes (e.g. seagrasses) and concomitant increases in microalgal production through eutrophication. Whether such changes translate into shifts in the composition of sediment detritus is largely unknown, yet such changes could impact the role these ecosystems play in sequestrating CO 2. We reconstructed the sedimentary records of cores taken from two sites within Botany Bay, Sydney - the site of European settlement of Australia - to look for human-induced changes in dominant sources of detritus in this estuary. Cores covered a period from the present day back to the middle Holocene (~6000 years) according to 210Pb profiles and radiocarbon ( 14C) dating. Depositional histories at both sites could not be characterized by a linear sedimentation rate; sedimentation rates in the last 30-50 years were considerably higher than during the rest of the Holocene. C : N ratios declined and began to exhibit a microalgal source signature from around the time of European settlement, which could be explained by increased nutrient flows into the Bay caused by anthropogenic activity. Analysis of stable isotopic ratios of 12C/ 13C showed that the relative contribution of seagrass and C 3 terrestrial plants (mangroves, saltmarsh) to detritus declined around the time of rapid industrial expansion (~1950s), coinciding with an increase in the contribution of microalgal sources. We conclude that the relative contribution of microalgae to detritus has increased within Botany Bay, and that this shift is the sign of increased industrialization and concomitant eutrophication. Given the lower carbon burial efficiencies of microalgae (~0.1%) relative to seagrasses and C 3 terrestrial plants (up to 10%), such changes represent a substantial weakening of the carbon sink potential of Botany Bay - this occurrence is likely to be common to human-impacted estuaries, and has consequences for the role these systems play in helping to mitigate climate change. © 2011 Blackwell Publishing Ltd.

Effects of diet change on carbon and nitrogen stable-isotope ratios in blood cells and plasma of the long-nosed bandicoot (Perameles nasuta)

Carbon (C) and nitrogen (N) stable isotopes offer a powerful tool for assessing the extent of tissue assimilation of dietary components. However, the method relies on knowledge of diet-tissue isotopic discrimination and how quickly diet shifts become apparent in various tissues. In the present study, blood plasma and blood cells, tissues that are easily obtained under field conditions, were used to validate the stable isotope method over a period of 4-5 weeks using captive long-nosed bandicoots (Perameles nasuta). Diet-tissue discrimination effects appeared to be small. For C, derived diet-tissue isotopic discriminations were 1.4‰ for blood plasma and -0.2‰ for blood cells. For N the values were 2.8‰ and 2.1‰, respectively, and were independent of the nitrogen content of the food. C and N turnover measurements in the blood plasma and cells of the bandicoots indicated that blood plasma provides dietary information integrated over a period of ∼3 weeks, whereas blood cells give an impression of the assimilated diet over a period of as much as half a year. These turnover rates were low compared with the little information available for birds and eutherian mammals, and probably relate to the typically low metabolic rate of marsupials.

Geographical variation and population structure in the White-rumped Sandpiper Calidris fuscicollis as shown by morphology, mitochondrial DNA and carbon isotope ratios

We studied the population structure of a high arctic breeding wader bird species, the White-rumped Sandpiper Calidris fuscicollis. Breeding adults, chicks and juveniles were sampled at seven localities throughout the species' breeding range in arctic Canada in 1999. The mitochondrial control region was analysed by DNA sequencing, feathers were analysed for carbon isotope ratios (C13/C12) by isotope ratio mass spectrometry, and morphological measurements were analysed using principal component analyses, taking the effect of sex into account (identified by molecular genetic methods). In general, our results support the notion that the White-rumped Sandpiper is a monotypic species with no subspecies, and most of the morphological and genetic variation occurs within sites. Nevertheless, some differences between sites were found. Birds from the two northernmost sites (Ellesmere and Devon Islands) had relatively longer bill and wing and shorter tarsus than birds sampled further south, possibly reflecting genetic differences between populations. The carbon isotope ratios were higher at the easternmost site (Baffin Island), revealing differences in the isotope content of the food. The mtDNA sequences showed no significant differentiation between sites and no pattern of isolation-by-distance was found. Based on the mtDNA variation, the species was estimated to have a long-term effective population size of approximately 9,000 females. The species shows no clear evidence of any population expansion or decline. Our results indicate that carbon isotope ratios, and possibly also certain mtDNA haplotypes, may be useful as tools for identifying the breeding origin of White-rumped Sandpipers on migration and wintering sites.

Losses and recovery of organic carbon from a seagrass ecosystem following disturbance

Seagrasses are among the Earth's most efficient and long-term carbon sinks, but coastal development threatens this capacity. We report new evidence that disturbance to seagrass ecosystems causes release of ancient carbon. In a seagrass ecosystem that had been disturbed 50 years ago, we found that soil carbon stocks declined by 72%, which, according to radiocarbon dating, had taken hundreds to thousands of years to accumulate. Disturbed soils harboured different benthic bacterial communities (according to 16S rRNA sequence analysis), with higher proportions of aerobic heterotrophs compared with undisturbed. Fingerprinting of the carbon (via stable isotopes) suggested that the contribution of autochthonous carbon (carbon produced through plant primary production) to the soil carbon pool was less in disturbed areas compared with seagrass and recovered areas. Seagrass areas that had recovered from disturbance had slightly lower (35%) carbon levels than undisturbed, but more than twice as much as the disturbed areas, which is encouraging for restoration efforts. Slow rates of seagrass recovery imply the need to transplant seagrass, rather than waiting for recovery via natural processes. This study empirically demonstrates that disturbance to seagrass ecosystems can cause release of ancient carbon, with potentially major global warming consequences.