Abstract: The Arctic experiences a rapid retreat of sea-ice, particularly in spring and summer, which may dramatically affect pagophilic species. In recent years, the decline of many Arctic seabird populations has raised concerns about the potential role of sea-ice habitats on their demography. Spring sea-ice drives the dynamics of phytoplankton blooms, the basis of Arctic food webs, and changes in spring sea-ice have the potential to affect the demographic parameters of seabirds through bottom-up processes. To better understand the effects of spring sea-ice on Arctic seabirds, we investigated the influence of spring sea-ice concentration on the survival and breeding success of three seabird species with contrasted foraging strategies in two Svalbard fjords in the high Arctic. We examined these relationships using long-term demographic data (2005–2021) from black-legged kittiwakes (Rissa tridactyla), Brünnich guillemots (Uria lomvia), and little auks (Alle alle). Spring sea-ice concentration was positively related to both the survival and breeding success of little auks, suggesting a higher sensitivity of this species to spring sea-ice. By contrast, the two other species were not particularly sensitive to changes in spring sea-ice, even though a potentially spurious negative effect on the breeding success of black-legged kittiwakes was observed. Overall, the study suggests that spring sea-ice may be involved in the demography of Arctic seabirds, but probably does not play a major role.

Abstract: Non-conventional stable isotopes have received increasing attention in the past decade to investigate multi-level ecological connections from individuals to ecosystems. More recently, isotopes from trace and non-nutrient elements, potentially toxic (i.e., Hg), have also been recognized of great significance to discriminate sources, transports, and bioaccumulation, as well as trophic transfers. In contrast, lithium (Li) concentrations and its isotope compositions (δ7Li) remain poorly documented in aquatic ecosystems, despite its possible accumulation in marine organisms, its increasing industrial production, and its demonstrated hazardous effects on biota. Here, we present the first Li isotope investigation of various soft tissues, organs or whole organisms, from marine plankton, bivalves, cephalopods, crustaceans, and fish of different biogeographical regions [North Mediterranean Sea, North Atlantic Ocean (Bay of Biscay), South East Pacific Ocean (New Caledonia), and Southern Indian Ocean (Kerguelen Islands)]. Independently of the considered organisms, δ7Li values range widely, from 4.6‰ (digestive gland of bivalves) to 32.0‰ (zooplankton). Compared to homogeneous seawater (δ7Li ∼ 31.2‰ ± .3‰), marine organisms mostly fractionate Li isotopes in favor of the light isotope (6Li). Within the same taxonomic group, significant differences are observed among organs, indicating a key role of physiology on Li concentrations and on the distribution of Li isotopes. Statistically, the trophic position is only slightly related to the average Li isotope composition of soft tissues of marine organisms, but this aspect deserves further investigation at the organ level. Other potential influences are the Li uptake by ingestion or gill ventilation. Overall, this work constitutes the first δ7Li extensive baseline in soft tissues of coastal organisms from different large geographic areas mostly preserved from significant anthropogenic Li contamination.

Abstract: The ocean’s meso- and submeso-scales (1-100 km, days to weeks) host features like filaments and eddies that have a key structuring effect on phytoplankton distribution, but that due to their ephemeral nature, are challenging to observe. This problem is exacerbated in regions with heavy cloud coverage and/or difficult access like the Southern Ocean, where observations of phytoplankton distribution by satellite are sparse, manned campaigns costly, and automated devices limited by power consumption. Here, we address this issue by considering high-resolution in-situ data from 18 bio-logging devices deployed on southern elephant seals (Mirounga leonina) in the Kerguelen Islands between 2018 and 2020. These devices have submesoscale-resolving capabilities of light profiles due to the high spatio-temporal frequency of the animals’ dives (on average 1.1 +-0.6 km between consecutive dives, up to 60 dives per day), but observations of fluorescence are much coarser due to power constraints. Furthermore, the chlorophyll a concentrations derived from the (uncalibrated) bio-logging devices’ fluorescence sensors lack a common benchmark to properly qualify the data and allow comparisons of observations. By proposing a method based on functional data analysis, we show that a reliable predictor of chlorophyll a concentration can be constructed from light profiles (14 686 in our study). The combined use of light profiles and matchups with satellite ocean-color data enable effective (1) homogenization then calibration of the bio-logging devices’ fluorescence data and (2) filling of the spatial gaps in coarse-grained fluorescence sampling. The developed method improves the spatial resolution of the chlorophyll a field description from ~30 km to ~12 km. These results open the way to empirical study of the coupling between physical forcing and biological response at submesoscale in the Southern Ocean, especially useful in the context of upcoming high-resolution ocean-circulation satellite missions.

Abstract: Wildlife movement ecology often focuses on breeders, whose territorial attachments facilitate trapping and following individuals over time. This leads to incomplete understanding of movements of individuals not actively breeding due to age, breeding failure, subordinance, and other factors. These individuals are often present in breeding populations and contribute to processes such as competition and pathogen spread. Therefore, excluding them from movement ecology studies could bias or mask important spatial dynamics. Loafing areas offer an alternative to breeding sites for capturing and tracking individuals. Such sites may allow for sampling individuals regardless of breeding status, while also avoiding disturbance of sensitive breeding areas. However, little is known about the breeding status of individuals attending loafing sites, or how their movements compare to those of breeders captured at nests. We captured a seabird, the brown skua, attending either nests or loafing areas (‘clubs’) at a multi-species seabird breeding site on Amsterdam Island (southern Indian Ocean). We outfitted skuas with GPS-UHF transmitters and inferred breeding statuses of individuals captured at clubs using movement patterns of breeders captured at nests. We then compared space use and activity patterns between breeders and nonbreeders. Both breeding and nonbreeding skuas attended clubs. Nonbreeders ranged more widely, were more active, and overlapped more with other seabirds and marine mammals than did breeders. Moreover, some nonbreeders occupied fixed territories and displayed more restricted movements than those without territories. Nonbreeders became less active over the breeding season, while activity of breeders remained stable. Nonbreeding skuas were exposed to the agent of avian cholera at similar rates to breeders but were more likely to forage in breeding areas of the endangered endemic Amsterdam albatross, increasing opportunities for interspecific pathogen transmission. Our results show that inference based only on breeders fails to capture important aspects of population-wide movement patterns. Capturing nonbreeders as well as breeders would help to improve population-level representation of movement patterns, elucidate and predict effects of external changes and conservation interventions (e.g. rat eradication) on movement patterns and pathogen spread, and develop strategies to manage outbreaks of diseases such as highly pathogenic avian influenza. Read the free Plain Language Summary for this article on the Journal blog.