# Predator-mediated nutrient transfers and recycling in ecosystems: Fine-scale variation in the contribution of Antarctic fur seals (Arctocephalus gazella) on and around the Kerguelen Islands

Lola Gilbert, Jérôme Spitz, Mathilde Chevallay, Tiphaine Jeanniard-Du-Dot

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Lola Gilbert, Jérôme Spitz, Mathilde Chevallay, Tiphaine Jeanniard-Du-Dot. Predator-mediated nutrient transfers and recycling in ecosystems: Fine-scale variation in the contribution of Antarctic fur seals (Arctocephalus gazella) on and around the Kerguelen Islands. Science of the Total Environment, 2025, 975, pp.179195. 10.1016/j.scitotenv.2025.179195. hal-05018577

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# Predator-mediated nutrient transfers and recycling in ecosystems: Fine-scale variation in the contribution of Antarctic fur seals (*Arctocephalus gazella*) on and around the Kerguelen Islands

Lola Gilbert<sup>a,b,*</sup>, Jérôme Spitz<sup>a,b</sup>, Mathilde Chevallay<sup>a</sup>, Tiphaine Jeanniard-du-Dot<sup>a</sup>

## HIGHLIGHTS

* Antarctic fur seal scat nutrient content shows high intra and inter-colony variability

* Essential nutrient release is associated to the release of potential pollutants

* Faecal nutrient release levels are significant at sea and on coastal colony sites

* Colony nutrient release levels reflect both abundance and scat composition patterns

* Spatial variation in faecal nutrient release suggests different ecosystem relevance

## GRAPHICAL ABSTRACT

<figure><img src="image_4.png" /></figure>

## ARTICLE INFO

Editor: Julian Blasco

### Keywords:

Animal-mediated nutrient cycling

Major element

Trace element

Trace metal

Contaminant

HNLC

## ABSTRACT

Waters on the Kerguelen Plateau are characterised by a high productivity and unique nutrient dynamics compared to the surrounding Southern Ocean. They support large populations of amphibious marine predators such as seabirds and marine mammals, which participate in nutrient recycling at sea and nutrient transfers from sea to land on their colonies. This study investigates the contribution of Antarctic fur seals (*Arctocephalus gazella*) to the biological recycling of 15 essential and 5 non-essential nutrients on and around the Kerguelen Islands during their four-month breeding season. Nutrient concentrations of 59 fur seal scats from two colonies were examined and used to determine faecal nutrient output from lactating females using a bioenergetic model. We evidenced individual variability in the multi-nutrient composition of fur seal scats, with different types of potential fertilisers. Colony differences in scat compositions resulted in multi-nutrient release levels that did not simply reflect colony abundances. This suggests that estimating predators' nutrient release based on averages (diets, prey or faecal nutrient contents) likely overlooks important fine-scale spatial variability in their contributions. Collectively, fur seals deposit up to 628 kg (95 % CI [548–710]) of phosphorus (limiting on land), 46.4 [39.8–53.2] kg of iron (limiting at sea), and 5.9 [5.2–6.8] g of lead (toxic to most organisms). At sea, fur seal defecation could trigger locally significant enrichment events. On land, fur seal faecal nutrient deposition is spatially concentrated in coastal colonies where phosphorus deposition is in the range of global crop fertiliser

<footnote><sup>a</sup> Centre d'Etudes Biologiques de Chizé (CEBC), UMR7372 CNRS - La Rochelle Université, 79360 Villiers-en-Bois, France</footnote>

<footnote><sup>b</sup> Observatoire Pelagis, UAR3462 CNRS - La Rochelle Université, 5 allées de l'océan 17000 La Rochelle, France</footnote>

<footnote>* Corresponding author at: Centre d'Etudes Biologiques de Chizé (CEBC), UMR7372 CNRS - La Rochelle Université, 79360 Villiers-en-Bois, France. E-mail addresses: lola.gilbert@lilo.org, lola.gilbert@univ-lr.fr (L. Gilbert).</footnote>
use. We argue that the role of marine predators in the local nutrient dynamics of the Kerguelen area should not be overlooked, and that fine-scale variability in the nutrient input by such marine predators is important to consider in any local nutrient dynamic study.

# 1. Introduction

Major nutrients such as nitrogen (N) or phosphorus (P) and trace elements such as iron (Fe), manganese (Mn) or cobalt (Co) are the building blocks of life on Earth (Lavelle et al., 2005). Their recycling within a given system or their transfer between systems are crucial in shaping the functioning of ecosystems (Atkinson et al., 2017; Marzetz et al., 2017). These nutrient fluxes are mediated by large-scale physical processes such as wind and currents, as well as by the biological processes. Animal food ingestion, digestion and metabolism facilitate the return of nutrients trapped in living matter (plant or prey) to a form that can be re-mobilised by primary producers in their environment, either directly or after remineralisation by the microbial community (Subalusky and Post, 2019). Even though they operate on a smaller scale than physical processes, animal-mediated nutrient recycling through waste (faeces and urine) can impact local productivity and biodiversity patterns (e.g., Bokhorst et al., 2019a; Doughty et al., 2016; Reimchen et al., 2003; Wolf et al., 2013), to such an extent that changes in the animal community can alter ecosystem functioning (Benkwitt et al., 2022, 2021; McIntyre et al., 2007).

The Southern Ocean (SO) is the largest High Nutrient Low Chlorophyll (HNLC) region in the world's oceans, which means its mixed layer is overall replete with major nutrients N or P, but the growth and productivity of primary producers are limited by low concentrations of essential trace nutrients, mainly Fe (Blain et al., 2007). Any addition of this nutrient can therefore stimulate the productivity throughout the food web if conditions are favourable (Blain et al., 2007; Boyd et al., 2000; Hassler et al., 2012). Within the SO, the Kerguelen Plateau region benefits from natural Fe fertilisation by a combination of physical processes such as upwelling and atmospheric dust (Blain et al., 2001; van Der Merwe et al., 2015). The Kerguelen Islands are also surrounded by the subtropical, sub-Antarctic and polar fronts, three circumpolar oceanographic currents that determine the SO nutrient background and fluxes (Bestley et al., 2020). As their natural flows are influenced by the physical barrier created by the Plateau, these fronts participate in creating the unique nutrient dynamics of the Kerguelen region (Chapman et al., 2020; Lefèvre et al., 2008).

Kerguelen waters are thus highly productive, and the Kerguelen Islands support large colonies of marine top predators such as Antarctic fur seals (Arctocephalus gazella), southern elephant seals (Mirounga leonina) and king penguins (Aptenodytes patagonicus). These amphibious air-breathing species breed, rest and moult on land, but feed at sea. They consume large quantities of diverse prey (Guinet et al., 2001) and subsequently produce faeces and urine enriched in ocean-derived essential major and trace nutrients (Belyaev et al., 2023; Wing et al., 2017, 2014). However, the contribution of marine predators to the biological recycling of nutrients both at sea and on the Kerguelen shores remains unknown despite extensive research on the nutrient and productivity dynamics of this region (e.g., Blain et al., 2008; D'Ovidio et al., 2015; Hunt et al., 2021; van Der Merwe et al., 2015).

This study examines the role of Antarctic fur seals in the recycling and transfer of nutrients in Kerguelen waters and in the coastal ecosystem of the Kerguelen Islands through the faecal material they release. Antarctic fur seals breeding on Kerguelen Islands spend the eight winter months at sea, and the four austral summer months on land to breed and moult. During breeding, reproductive females (and sub-adults) alternate foraging trips at sea with land-based bouts. When at sea, they can transport nutrients from their predation point at depth to the surface where they defecate when they come to breathe, rest and travel. They can also operate a horizontal transport to different

geographical locations given the time needed for digestion, possibly against physical forces such as wind and currents (McInturf et al., 2019; Roman and McCarthy, 2010; Wing et al., 2021, 2017). Whale, seal and seabird's faeces can stimulate phytoplankton and microbial growth and influence their community structure (Alba-González et al., 2022; Shatova et al., 2017; Smith et al., 2013), so the local fur seal-mediated nutrient enrichment could locally enhance productivity and influence trophic dynamics. In addition, marine predators such as fur seals release some waste (faeces and urine) into terrestrial and coastal ecosystems when they come ashore to their colony sites (Smith, 2008). These cross-ecosystem nutrient transfers from sea to land can have a structuring effect on soil enrichment and development (Ball et al., 2015; Benkwitt et al., 2021; Bokhorst et al., 2007) and have a positive influence on the abundance and diversity of soil and plant communities (Bokhorst et al., 2019a). Fur seals, along with the other amphibious marine predators, could thus participate in shaping the heterogeneity of coastal sub-Antarctic and Antarctic lands (Bokhorst et al., 2019a; Erskine et al., 1998; Smith, 2008), although it operates at different spatio-temporal scales than the physical processes involved in setting the unique context of the Kerguelen region.

To investigate this, we first analysed the nutrient composition of Antarctic fur seal scats collected in two Kerguelen colonies for 15 essential nutrients (i.e., with known biological functions and deleterious effects in their absence; including five major and ten trace nutrients) and five non-essential nutrients (i.e., with no identified biological function and potential toxicity). Stoichiometry - the relative ratio between nutrients within a mixture - is critical to the ecosystem response to any nutrient input, as each species has specific needs and tolerance levels (Ballantyne IV et al., 2008; Pichon et al., 2013; Sitters et al., 2015). Furthermore, the cycling of essential nutrients is coupled with the cycling and transfer of non-essential nutrients, which can also shape the ecosystem response. Even for essential nutrients, the window between deficient, adequate and toxic levels can be relatively narrow, depending on the context. This multi-nutrient approach is therefore necessary to provide a complete picture of the processes involved (Sitters et al., 2015). The scat compositions were then used in a bioenergetic model framework to quantify faecal nutrients released by lactating Antarctic fur seal females from the two colonies during an Austral summer, when they forage at sea and return to land to support their young at the breeding colony. Ultimately, this study aims to provide a better functional understanding of the quantitative, qualitative, spatial and temporal contribution of fur seals to the biological recycling of nutrients in the coupled marine and terrestrial ecosystems they live in, and at different scales (individual, colony).

# 2. Material & Methods

## 2.1. Field sampling and data collection

Sixty Antarctic fur seal scats were collected on two colonies on the Kerguelen Islands, at Cap Noir (Courbet Peninsula, 49°07′ S 70°45′ E, 29 samples) and at Pointe Suzanne (Courbet Peninsula, 49°44′ S 70°44′ E, 31 samples) during Austral summer 2021–2022. Samples were collected on the colony in clean plastic bags and were of varying degrees of freshness. Scats were not identified to any individual, so it is unknown whether they were emitted by mature males, females or immature individuals. However, there is approximately 1 mature male for 5–10 mature females (based on Guinet et al. (1996) and our own experience), so they are more likely to be from females. Samples were stored at –20 °C within 48 h of collection and until processing.
Antarctic fur seal pups were counted on Cap Noir and Pointe Suzanne colonies by two to three operators independently as an index of number of breeding females (one female per pup), between late December 2022 and mid-January 2023 (Austral summer 2022–2023). Pups were counted separately along the landside of the colony, and on the beach. Counts started at dawn at both sites, when the majority of animals were resting on land. At Pointe Suzanne, three counts were carried out within 15 days. In Cap Noir, only one count was carried out by three operators, due to a shorter stay. Pup counts served as an input in our bioenergetic model (detailed below).

## 2.2. Sample processing and nutrient composition analysis

Scat samples were individually thawed, cleaned of large plant debris, weighed and stored at -20 °C before being freeze-dried for a minimum of 72 h and ground to fine powder until analysis.

Total concentrations of 6 major constitutive chemical elements in biological tissues (calcium Ca, phosphorus P, potassium K, sodium Na, magnesium Mg and strontium Sr) were determined by inductively coupled plasma atomic emission spectrometry (ICP-OES, Vista-Pro Varian). Note that although Sr is a major nutrient for its relatively high concentrations in biological tissues, it is considered non-essential (Chowdhury and Blust, 2011). Aliquots of samples (≈250 mg dry mass of homogenised powder) were digested using a 6:2 (v/v) mixture with nitric acid (HNO₃ 69 %, Trace Metal Grade®, FisherScientific) and hydrochloric acid (HCl, 34 %, Trace Metal Grade®, FisherScientific). Acidic digestion of the samples was performed over-night at room temperature and then in a microwave oven (START-D, Milestone). Finally, the digests were diluted to 50 mL with ultrapure water before analyses with ICP-OES. Total concentrations of 10 essential trace nutrients (iron Fe, zinc Zn, copper Cu, manganese Mn, selenium Se, nickel Ni, vanadium V, arsenic As, cobalt Co, molybdenum Mo) and 4 non-essential trace nutrients (cadmium Cd, chromium Cr, silver Ag and lead Pb) were determined by inductively coupled plasma mass spectrometry (ICP-MS, ICAP-Qc ThermoFisher). Aliquots of samples (≈200 mg dry mass of homogenised powder) were placed in Teflon bombs and mineralized with a mixture of ultrapure HNO₃ acid (PlasmaPure Plus grade, SCP Science®) and ultrapure water using a micro-wave (ETHOS-UP, Milestone). The digests were then diluted to 50 mL with ultrapure water before analyses with ICP-MS. The quality assurance of all metal analyses relied on blank and internal standard controls, and on the accuracy and reproducibility of data relative to the certified reference materials (CRMs) used in each analytical run. Blank values were systematically below the detection limits and CRM values concurred with certified concentrations.

For Sr, V, Cr, Pb and Mo, few concentrations were under limits of quantification (LOQ), which were calculated for each sample depending on the mass of the aliquot analysed. Depending on nutrients, this concerned 2 to 27 % of samples, so to keep these samples we set concentrations of corresponding samples to half of the sample LOQ. One sample was identified as a technical outlier and removed from the dataset, so we conducted the analysis using 59 samples.

## 2.3. Variability and typology of scats' nutrient composition

We first estimated the variability in absolute nutrient concentrations of fur seal scats with a nutrient-by-nutrient approach using basic descriptive statistics, boxplots and Mann Whitney Wilcoxon (MWW) non-parametric tests to compare concentrations in scat samples collected on the two colonies. We also examined the variability in the relative nutrient composition (i.e., stoichiometry) of each sample by calculating a concentration ratio in the mix of nutrients considered here, e.g., for the relative proportion of Ca in a given sample the calculation was the sample absolute concentration in Ca divided by the sum of the concentrations in Ca, P, Mg, Na, K, Fe, Zn, Sr, Cu, Mn, Se, Ni, V, As, Co, Mo, Cd, Cr, Ag and Pb.

Then, we used hierarchical clustering (HC) on samples for each colony separately to (i) identify relative similarity between samples and groups of samples in terms of concentrations in multiple nutrients, (ii) identify nutrients that are the most discriminating between these groups and (iii) assess potential spatial differences in the multi-nutrient typology of fur seal scats. Clustering with high dimension can cause problems in differentiating similar and dissimilar objects, and this “curse of dimensionality” can occur with as few as ten dimensions (Assent, 2012). We thus performed a Principal Component Analysis (PCA) to reduce the number of dimensions of the datasets (originally, 20 nutrients, hence 20 dimensions). We then used coordinates of samples on the first principal components of the PCA as an input for the HC analysis, selecting the first principal components that together explained at least 95 % of the datasets' variance (five for both Cap Noir and Pointe Suzanne samples).

Classical statistical methods (such as PCA and HC) are unsuitable to analyse composition data, because they rely on Euclidean geometry (Filzmoser et al., 2018). Thus, for the PCA the scat composition data was transformed and expressed in isometric log-ratio coordinates before performing a robust PCA (Filzmoser et al., 2009; Filzmoser and Hron, 2009; Templ and Templ, 2021) using an algorithm designed for composition datasets provided in Robcomposition R package (Templ et al., 2011). We detected four statistical outlier concentration values for different nutrients and different samples, which were replaced with values of the 98 % percentile of the corresponding nutrient to keep the samples while limiting their influence in the PCA.

For the HC, we used a classical algorithm based on Ward's minimum variance method (Ward, 1963) because the input data (i.e., samples' coordinates on the PCA first five principal components) was no longer compositional in nature. We selected the optimal number of clusters in each colony using PCA biplots, dendrograms and standard validating measures (e.g., average distance within and between clusters, minimum cluster size). Nutrient concentrations in samples from the resulting clusters were described nutrient-by-nutrient using basic descriptive statistics and boxplots. We also computed MWW tests to assess the statistical significance of nutrient-by-nutrient differences between clusters in each colony and between clusters of the two colonies.

## 2.4. Faecal nutrient release by lactating female fur seals from each colony

We used a bioenergetic model to estimate fur seals' daily needs and food consumption, and extended it to estimate dry faecal matter production and faecal nutrient release.

### 2.4.1. Colony abundance of lactating female fur seals

The population structure of the fur seal colonies in the Kerguelen Islands was never assessed, so the proportion of mature males, breeding females and immature individuals is unknown at Cap Noir and Pointe Suzanne. The strong sexual dimorphism of this species (Shirihai, 2008) would require to set specific metabolic parameters for each sex and life stage (body mass, energy requirements). In addition, mature and immature males and females likely have different foraging strategies and ecologies, and therefore different time allocated to being at sea or staying on land (Green et al., 1989; Jones et al., 2021; March et al., 2021; Staniland and Robinson, 2008). For example, lactating females divide their time between sea and land to balance the constraints of pup care given their limited fasting capacity, whereas mature males fast while maintaining harem territories (Goldsworthy, 2008). Lactating females are the most numerous part of the population feeding at sea on breeding colonies (Page et al., 2003). Thus, as a first index we quantified faecal nutrient release only for lactating females on the two breeding colonies of Cap Noir and Pointe Suzanne. We limited our estimate to the breeding and moulting period, which lasts from December to March on the Kerguelen Islands (≈ 4 months), when lactating female fur seals alternate between foraging trips at sea and land-based bouts (Shirihai, 2008). Outside of this period, they remain fully at sea and their whereabouts and behaviour are poorly known.
<caption>**Table 1**</caption>

Bioenergetic model parameters settings (distribution, mean $\bar{x}$, standard deviation sd, lower limit a and upper limit b) to estimate faecal nutrient release levels by lactating female Antarctic fur seals (*Arctocephalus gazella*) in the Kerguelen Islands (Southern Ocean), with references used.

<table><thead><tr><th>Model parameter</th><th>Distribution</th><th>Distribution parameters</th><th>Reference</th></tr></thead><tbody><tr><td>Body mass BM (kg)</td><td>Truncated normal</td><td>x̄ = 27<br>sd = 5<br>a = 20<br>b = 38</td><td>Jeanniard-du-Dot and Guinet, 2021</td></tr><tr><td>Metabolic multiplier when on land β<sub>land</sub></td><td>Truncated normal</td><td>x̄ = 3.3<br>sd = 0.1<br>a = 2<br>b = 4.5</td><td>Jeanniard-du-Dot et al., 2017b</td></tr><tr><td>Metabolic multiplier when at sea β<sub>sea</sub></td><td>Truncated normal</td><td>x̄ = 4.7<br>sd = 0.3<br>a = 3.5<br>b = 6.5</td><td>Arnould et al., 1996; Boyd, 2002; Costa et al., 1989; Jeanniard-du-Dot et al., 2017b</td></tr><tr><td>Assimilation efficiency AE</td><td>Truncated normal</td><td>x̄ = 0.85<br>sd = 0.05<br>a = 0.8<br>b = 0.9</td><td>Booth et al., 2023</td></tr><tr><td>Average energy content of diet E (in kJ·kg<sup>-1</sup> wet weight)</td><td>Truncated normal</td><td>x̄ = 7,750<br>sd = 2,470<br>a = 4,000<br>b = 13,000</td><td>Jeanniard-du-Dot et al., 2017a</td></tr><tr><td>Diet dry matter content DM<sub>R</sub></td><td>Uniform</td><td>a = 0.15<br>b = 0.25</td><td>Chouvelon et al., 2022a</td></tr><tr><td>Dry matter release rate r<sub>DM</sub></td><td>Uniform</td><td>a = 0.09<br>b = 0.17</td><td>Keiver et al., 1984; Ronald et al., 1984</td></tr><tr><td>Days present on site d</td><td>Uniform</td><td>a = 100<br>b = 140</td><td>Shirihai, 2008</td></tr><tr><td>% of time spent on land t<sub>land</sub></td><td>Uniform</td><td>a = 0.15<br>b = 0.35</td><td>Boyd, 1999; Boyd et al., 1991; Doidge and Croxall, 1989; Goldsworthy, 1999</td></tr><tr><td>Abundance of lactating females on colony A (No.)</td><td>Uniform</td><td>a = min pup count<br>b = maxpup count + 0.2*maxpup count</td><td></td></tr></tbody></table>

The model was set up using Monte-Carlo simulations to simulate uncertainty and variability for each model parameter, starting with the abundance of lactating female fur seals on each colony site. With visual pup counts, the abundance may be negatively biased because pups are more likely missed than counted twice. The fur seals are in a vegetated area where the topography can be uneven, there are holes and the vegetation can be high enough to hide pups when viewed from a distance, although it is relatively flat. They also stay around the beach limit where they can be hidden behind boulders and rocks. For pup censuses of a related species that breed in similar conditions, the subantarctic fur seal *Arctocephalus tropicalis*, the pup undercount has been estimated between 14.2 and 34.3% (Bester et al., 2003; Hofmeyr et al., 1997). In addition, in our case the counts were conducted some time after the peak of pup production (late November - early December), which means that a number of reproductive females were not taken into account, given the perinatal mortality of pups (Hofmeyr et al., 1997; Reid and Forcada, 2005). We therefore considered that lactating female abundance A followed a uniform distribution with minimum set as the minimum pup count and maximum as the maximum pup count +20% for each colony (Table 1), and we performed 5000 simulations to account for the uncertainty in this number.

Then, the bioenergetic model was set up at the individual level to estimate dry faecal matter production and faecal nutrient release.

### 2.4.2. Individual dry faecal matter production

Average Daily Metabolic Rate (ADMR, in kJ·day⁻¹) was estimated based on the Basal metabolic rate (BMR, in kJ·day⁻¹) using Kleiber (1975) formula (previously applied to marine mammal populations, e.g., Barlow et al., 2008; Roman and McCarthy, 2010; Spitz et al., 2018) and including the additional cost of daily activities through the species-specific metabolic index β (Spitz et al., 2018, 2012). For an individual i:

$$ADMR_i = \beta_i \times BMR_i = \beta_i \times 293.1 \times BM_i^{3/4} \quad (1)$$

where BM stands for body mass (in kg). Costs of daily activities are different on land or at sea (Jeanniard-du-Dot et al., 2017b), as fur seals feed at sea and fast on land when nursing their pup. We thus used specific metabolic indices β<sub>land</sub> and β<sub>sea</sub> to compute ADMR<sub>land</sub> and ADMR<sub>sea</sub> from eq. 1. We also accounted for the percentage of time fur seal females spent on land (t<sub>land</sub>) versus at sea (1 - t<sub>land</sub>) during the breeding season to estimate the ration R (in kg·day⁻¹) needed for each individual to meet its ADMR, considering the mean energy content of its diet (E, in kJ·kg⁻¹ fresh weight) and the digestive assimilation efficiency (AE):

$$R_i = \frac{ADMR_{land} \times t_{land} + AMDR_{sea} \times (1 - t_{land})}{AE \times E_i} \quad (2)$$

This ration R<sub>i</sub> represents the average daily ration if a fur seal i were to feed everyday throughout the breeding and moulting season in the model, but it is actually consumed only during foraging bouts at sea. Similarly, we estimated individual dry faecal matter production for one daily ration F<sub>DM,i</sub> (in kg) based on the dry matter content of this daily ration DM<sub>Ri</sub> and on the individual dry matter release rate r<sub>DM,i</sub>:

$$F_{DM,i} = R_i \times DM_{Ri} \times r_{DM,i} \quad (3)$$

Then, we estimated the individual total dry faecal matter production over the breeding and moulting period t, assuming an even distribution of defecation events throughout the period. The duration of this period likely varies between individuals (depending on pup birth date, pup care requirements, moulting duration, for example), so each estimate of individual faecal dry matter production for one daily ration was multiplied by a duration (d in days):

$$F_{DM,i,t} = F_{DM,i} \times d_i \quad (4)$$

### 2.4.3. Individual faecal nutrient release

We estimated the amounts of faecal nutrients released by each individual over the breeding period using dry matter nutrient concentrations of collected scats as follows:
$$N_{n,i,t} = F_{DM,i,t} \times x_{n,i} \qquad (5)$$

where $N_{n,i,t}$ (in kg) is the total amount of faecal nutrient $n$ released in the faeces of individual $i$ over the breeding and moulting period $t$, and $x_{n,i}$ is the concentration of nutrient $n$ in this individual's faeces (in $mg \cdot kg^{-1}$ dry weight, hereafter dw). Scat samples were bootstrapped with resampling, and each individual in the colony was randomly assigned a scat sample with its specific nutrient concentrations.

We aimed to quantify how much of the faecal nutrients are released at sea during foraging bouts and on land-based colony sites, because of the contrasted biogeochemical and ecosystem dynamics in these two environments. To do so, we assumed that the proportion of defecation occurring at sea and on land was proportional to the time spent in each environment. We therefore used the average proportion of time spent on land by each individual lactating fur seal $t_{land}$ during the period $t$ to estimate faecal nutrient release of nutrient $n$ by individual $i$ on land $N_{n,i,t}$, land and at sea $N_{n,i,t,sea}$ throughout the period $t$:

$$N_{n,i,t,land} = N_{n,i,t} \times t_{land} \qquad (6)$$

$$N_{n,i,t,sea} = N_{n,i,t} \times (1 - t_{land}) \qquad (7)$$

### 2.4.4. Faecal nutrient release by lactating female fur seals from each colony: Total, at sea and on land

Faecal nutrient release at the colony level was finally estimated based on colony lactating female abundance $A$, distinguishing the amounts released at sea during foraging sea bouts $N_{n,t,sea}$ (in kg) of that released on land at colony sites during the land-based bouts when females nurse their pups $N_{n,t,land}$, and the total $N_{n,t}$:

$$N_{n,t,land} = \sum_{i=1}^{A} N_{n,i,t,land} \qquad (8)$$

$$N_{n,t,sea} = \sum_{i=1}^{A} N_{n,i,t,sea} \qquad (9)$$

$$N_{n,t} = N_{n,t,land} + N_{n,t,sea} = \sum_{i=1}^{A} N_{n,i,t} \qquad (10)$$

It should be noted that for simplicity, we refer to these terms as the “colony levels” (e.g., to compare results for the two colonies), although they only include the contribution of lactating females, excluding that of mature males, immature subadults and pups.

### 2.4.5. Modelled variability in individual parameters

Individual BM, $\beta_{sea}$, $\beta_{land}$, E and AE were defined using truncated normal distributions, with average, lower and upper limits set based on the literature (Table 1). Body mass for lactating females was set with a mean of 27 kg and a standard deviation of 20 %, and with 20 and 38 as lower and upper limits, respectively (Jeanniard-du-Dot and Guinet, 2021). $\beta_{land}$ was set with a mean of 3.3 and a standard deviation of 0.1 and $\beta_{sea}$ with a mean of 4.7 and a standard deviation of 0.3, with minima and maxima set according to measured values (Arnould et al., 1996; Costa et al., 1989; Jeanniard-du-Dot et al., 2017b). Average energy content of the diet E and associated standard deviation were taken from Jeanniard-du-Dot et al. (2017a), and lower and upper limits were set based on minimum and maximum energy density of identified prey species (Jeanniard-du-Dot et al., 2017a) (Table 1). Assimilation efficiency AE was defined as $0.85 \pm 0.05$, based on experimental studies on captive pinnipeds (Booth et al., 2023). Fish water content approximates 80 % (Chouvelon et al., 2022a, 2022b; Nordøy et al., 1993), so we defined the dry matter content of the diet DM$_R$ as following a uniform distribution between 15 and 25 %. Similarly, individual dry matter release rate $r_{dm}$ was defined as following a uniform distribution between 10 and 20 % (Ronald et al., 1984) (Table 1). The individual duration of the breeding and moulting period $d$ was assumed to follow a uniform distribution with lower and upper bounds of 100 and 140 days (i.e., from 3.3 months to 4.7 months).

Finally, lactating females alternate between 7–8 d foraging trips at

sea and 2–4 d nursing on land on average (Boyd, 1999; Boyd et al., 1991; Doidge and Croxall, 1989; Guinet et al., 2001; Jeanniard-du-Dot et al., 2017b; Lea et al., 2002a, 2002b, 2008), although the duration of foraging and pup attendance bouts vary throughout the season (Goldsworthy, 1995; Luque et al., 2007). The average proportion of time spent on land by each individual lactating fur seal during this period, $t_{land}$, was therefore assumed to follow a uniform distribution between 15 and 35 % (Table 1). It should be noted that both sea- and land-based bouts show a possible period without defecation due to extended fasting. However, given the variability of the food passage rate (from 5 to over 80 h in fur seals; Staniland, 2002), the foraging trip duration, the time between the last foraging activity and arrival on land (no report found), the land-based bout duration and the time between departure from land and the first foraging activity ($\approx 4–9$ h; Bonadonna et al. 2000), we aimed for simplicity and considered $t_{land}$ as a direct index of the proportion of defecation occurring on land (and 1- $t_{land}$ as a direct index of the proportion of defecation occurring at sea).

We used the simulated lactating female abundance estimates (i.e., each of the 5000 possible values) as the number of simulations for Monte-Carlo simulations of individual parameters. That is to say that a colony abundance of $x$ lactating female fur seals was defined by $x$ individual random samplings of BM, $\beta_{land}$, $\beta_{sea}$, E, AE, DM$_R$, $r_{dm}$, d, $t_{land}$ using the distributions described. For example, for BM we drew $x$ values in truncated N ~ (BM = 27, sd$_BM$ = 5.4, BM$_{min}$ = 20, BM$_{max}$ = 38) to simulate the $x$ lactating females of the colony (Table 1). In addition, for each simulated lactating female abundance $x$ we generated a simulated scat composition dataset with $x$ samples using a bootstrap procedure with resampling from our collected scat samples, so that each individual in the simulated lactating female population was attributed to a specific scat composition. Samples were separated per colony to create the simulated scat composition datasets, i.e., only samples from Cap Noir were used for faecal nutrient release estimates at Cap Noir, and only samples from Pointe Suzanne were used for estimates at Pointe Suzanne.

### 2.4.6. Statistical assessment of differences

Given the aforementioned Monte-Carlo simulations and bootstrap procedures, our bioenergetic model outputs provide high-dimension results ($N = 5000$) which prevents the use of standard comparison statistical test (e.g., comparisons between colonies). Instead, we assessed unilateral binary relationships by calculating the percentage of values from one set of estimates that were superior to the compared set of estimates. We considered the difference to be significant when this percentage $p$ was either $\ge 95\%$ or $\le 5\%$ and we expressed $p$-values as $|0-p|$ as in classic statistical tests (i.e., difference significant for $p \le 0.05$). It should be noted that with this method, and unlike with classic statistical tests, our $p$ can be equal to 0 or 1.

## 3. Results

### 3.1. Faecal nutrient content of Antarctic fur seal scats

Results of absolute faecal nutrient concentrations in the 59 individual fur seal scat samples are available in InDoRes (Inventaire des Données de la Recherche en Environnement et Sociétés) at doi:10.48579/PRO/9P R5YU. Among the major essential nutrients, Ca was the most concentrated in Antarctic fur seal scats (mean $\pm$ standard deviation sd 77,861 $\pm$ 76,048 $mg \cdot kg^{-1}$ dw), and K the least concentrated (2294 $\pm$ 1098 $mg \cdot kg^{-1}$ dw; Table 2). For essential trace nutrients, Fe was the most concentrated in fur seal scats (3584 $\pm$ 4402 $mg \cdot kg^{-1}$ dw) with concentrations one order of magnitude more concentrated than Zn and Cu, two orders of magnitude more concentrated than Mn, Se and Ni, three orders of magnitude more concentrated than V and Co and four orders of magnitude more concentrated than Mo, the least concentrated essential trace nutrient (4.87 $\pm$ 3.75e$^{-1}$ $mg \cdot kg^{-1}$ dw; Table 2). The most concentrated non-essential trace nutrient was Sr (254 $\pm$ 214 $mg \cdot kg^{-1}$ dw).
<caption>**Table 2**</caption>

Statistics for nutrient concentrations (in mg•kg⁻¹ dry weight) in 59 scat samples from Antarctic fur seals (*Arctocephalus gazella*) collected on two colonies (Cap Noir and Pointe Suzanne) of the Kerguelen Islands, Southern Ocean. Colony concentrations in bold are significantly different according to Mann Whitney Wilcoxon non-parametric tests (*p* value <0.05), stat. Stands for statistics, med. is the median, sd the standard deviation, cv the coefficient of variation, min the minimum concentration and max the maximum concentration. The four last nutrients in the right of the table are considered as non-essential and potentially toxic nutrients (note that strontium Sr has no any known biological function but has been included with essential nutrients due to its high concentrations in biological tissues). The raw results of absolute nutrient concentrations are available in InDoRes (*Inventaire des Données de la Recherche en Environnement et Sociétés*) at doi:10.48579/PRO/9PR5YU.

<table><thead><tr><th>Colony</th><th>Stat.</th><th>Ca</th><th>P</th><th>Mg</th><th>Na</th><th>K</th><th>Fe</th><th>Zn</th><th>Sr</th><th>Cu</th><th>Mn</th><th>Se</th><th>Ni</th><th>V</th><th>As</th><th>Co</th><th>Mo</th><th>Cd</th><th>Cr</th><th>Ag</th><th>Pb</th></tr></thead><tbody><tr><td rowspan="6">Cap Noir</td><td>mean</td><td>64,609</td><td>41,035</td><td>10,244</td><td>6,823</td><td>2,167</td><td><strong>3,743</strong></td><td><strong>500</strong></td><td>199</td><td><strong>310</strong></td><td>74.6</td><td><strong>39.8</strong></td><td>13.8</td><td>4.53</td><td>3.29</td><td>3.09</td><td>0.530</td><td>15.6</td><td>3.06</td><td><strong>0.93</strong></td><td>0.145</td></tr><tr><td>med.</td><td>30,242</td><td>21,966</td><td>9,755</td><td>6,163</td><td>1,999</td><td><strong>2,074</strong></td><td><strong>495</strong></td><td>139</td><td><strong>234</strong></td><td>55.0</td><td>32.8</td><td>8.8</td><td>2.50</td><td>3.21</td><td>1.86</td><td>0.455</td><td>8.6</td><td>2.96</td><td><strong>0.57</strong></td><td>0.095</td></tr><tr><td>sd</td><td>72,116</td><td>41,037</td><td>4,853</td><td>3,035</td><td>852</td><td><strong>4,504</strong></td><td><strong>265</strong></td><td>192</td><td><strong>283</strong></td><td>59.0</td><td>29.3</td><td>14.0</td><td>4.87</td><td>1.19</td><td>3.39</td><td>0.414</td><td>28.8</td><td>2.97</td><td><strong>1.00</strong></td><td>0.153</td></tr><tr><td>cv</td><td>1.1</td><td>1</td><td>0.5</td><td>0.4</td><td>0.4</td><td><strong>1.2</strong></td><td><strong>0.5</strong></td><td>1.0</td><td><strong>0.9</strong></td><td>0.8</td><td>0.7</td><td>1.0</td><td>1.1</td><td>0.4</td><td>1.1</td><td>0.8</td><td>1.8</td><td>1.0</td><td><strong>1.1</strong></td><td>1.1</td></tr><tr><td>min</td><td>1,196</td><td>2,007</td><td>810</td><td>1,242</td><td>712</td><td><strong>149</strong></td><td><strong>76</strong></td><td>3</td><td><strong>14</strong></td><td>12.6</td><td>3.8</td><td>0.5</td><td>0.49</td><td>1.02</td><td>0.11</td><td>0.02</td><td>0.1</td><td>0.08</td><td><strong>0.03</strong></td><td>0.005</td></tr><tr><td>max</td><td>222,257</td><td>129,586</td><td>6</td><td>21,633</td><td>13,804</td><td>4,675</td><td><strong>16,909</strong></td><td><strong>1,092</strong></td><td>578</td><td><strong>1,272</strong></td><td>212.5</td><td>126.5</td><td>58</td><td>21.54</td><td>5.62</td><td>13.14</td><td>2.195</td><td>146</td><td>10.63</td><td><strong>3.72</strong></td><td>0.487</td></tr><tr><td rowspan="6">Pointe Suzanne</td><td>mean</td><td>89,831</td><td>52,578</td><td>9,014</td><td>6,336</td><td>2,409</td><td><strong>3,441</strong></td><td><strong>354</strong></td><td>303</td><td><strong>104</strong></td><td>107</td><td><strong>23.6</strong></td><td>18.9</td><td>5.43</td><td>4.07</td><td>2.72</td><td>0.448</td><td>6.24</td><td>6.91</td><td><strong>0.46</strong></td><td>0.653</td></tr><tr><td>med.</td><td>69,319</td><td>37,050</td><td>8,212</td><td>6,180</td><td>2,228</td><td><strong>972</strong></td><td><strong>315</strong></td><td>274</td><td><strong>54</strong></td><td>29</td><td>17.3</td><td>4.0</td><td>1.51</td><td>3.63</td><td>0.67</td><td>0.455</td><td>4.74</td><td>3.68</td><td><strong>0.14</strong></td><td>0.091</td></tr><tr><td>sd</td><td>78,667</td><td>45,688</td><td>4,724</td><td>3,281</td><td>1,285</td><td><strong>4,377</strong></td><td><strong>211</strong></td><td>224</td><td><strong>110</strong></td><td>134</td><td>18.8</td><td>25.1</td><td>7.17</td><td>2.62</td><td>3.30</td><td>0.339</td><td>6.52</td><td>8.33</td><td><strong>0.65</strong></td><td>0.956</td></tr><tr><td>cv</td><td>0.9</td><td>0.9</td><td>0.5</td><td>0.5</td><td>0.5</td><td><strong>1.3</strong></td><td><strong>0.6</strong></td><td>0.7</td><td><strong>1.1</strong></td><td>1.3</td><td>0.8</td><td>1.3</td><td>1.3</td><td>0.6</td><td>1.2</td><td>0.8</td><td>1.0</td><td>1.2</td><td><strong>1.4</strong></td><td>1.5</td></tr><tr><td>min</td><td>5,283</td><td>3,966</td><td>1,263</td><td>1,013</td><td>870</td><td><strong>26</strong></td><td><strong>23</strong></td><td>11</td><td><strong>15</strong></td><td>9.3</td><td>1.6</td><td>0.5</td><td>0.49</td><td>0.13</td><td>0.06</td><td>0.02</td><td>0.04</td><td>0.05</td><td><strong>0.03</strong></td><td>0.005</td></tr><tr><td>max</td><td>235,647</td><td>138,133</td><td>3</td><td>21,325</td><td>16,364</td><td>8,100</td><td><strong>13,363</strong></td><td><strong>912</strong></td><td>670</td><td><strong>402</strong></td><td>474.5</td><td>85.2</td><td>74.6</td><td>23.5</td><td>12.0</td><td>9.61</td><td>1.238</td><td>28.1</td><td>27.7</td><td><strong>2.10</strong></td><td>3.365</td></tr><tr><td rowspan="6">Cap Noir + Pointe Suzanne</td><td>mean</td><td>77,861</td><td>47,100</td><td>9,597</td><td>6,567</td><td>2,294</td><td>3,584</td><td>423</td><td>254</td><td>202</td><td>91.5</td><td>31.3</td><td>16.5</td><td>5.00</td><td>3.70</td><td>2.89</td><td>0.487</td><td>10.7</td><td>5.08</td><td>0.66</td><td>0.412</td></tr><tr><td>med.</td><td>50,325</td><td>37,050</td><td>9,017</td><td>6,180</td><td>2,228</td><td>1,843</td><td>394</td><td>187</td><td>115</td><td>41.7</td><td>24.5</td><td>4.6</td><td>1.93</td><td>3.43</td><td>1.22</td><td>0.464</td><td>6.6</td><td>3.19</td><td>0.24</td><td>0.091</td></tr><tr><td>sd</td><td>76,048</td><td>43,559</td><td>4,785</td><td>3,149</td><td>1,098</td><td>4,402</td><td>247</td><td>214</td><td>233</td><td>106</td><td>25.4</td><td>20.6</td><td>6.15</td><td>2.09</td><td>3.32</td><td>0.375</td><td>20.8</td><td>6.61</td><td>0.86</td><td>0.741</td></tr><tr><td>cv</td><td>1.0</td><td>0.9</td><td>0.5</td><td>0.5</td><td>0.5</td><td>1.2</td><td>0.6</td><td>0.8</td><td>1.2</td><td>1.2</td><td>0.8</td><td>1.3</td><td>1.2</td><td>0.6</td><td>1.1</td><td>0.8</td><td>1.9</td><td>1.3</td><td>1.3</td><td>1.8</td></tr><tr><td>min</td><td>1,196</td><td>2,007</td><td>810</td><td>1,013</td><td>712</td><td>26</td><td>23</td><td>3</td><td>14</td><td>9.3</td><td>1.6</td><td>0.5</td><td>0.49</td><td>0.13</td><td>0.06</td><td>0.02</td><td>0.04</td><td>0.05</td><td>0.03</td><td>0.005</td></tr><tr><td>max</td><td>235,647</td><td>138,133</td><td>3</td><td>21,633</td><td>16,364</td><td>8,100</td><td>16,909</td><td>1,092</td><td>670</td><td>1,272</td><td>474.5</td><td>126.5</td><td>74.6</td><td>23.5</td><td>12.0</td><td>13.14</td><td>2.195</td><td>146</td><td>27.7</td><td>3.72</td><td>3.365</td></tr></tbody></table>

dw) and the least Pb (4.12 ± 7.41e⁻¹ mg•kg⁻¹ dw; Table 2). Nutrient concentrations in scats showed high coefficients of variation ranging from 0.5 (for Na, K and Mg) to 1.2 (for Fe, Cu, Mn, Ni and V) for essential nutrients and from 0.8 (for Sr) to 1.9 (for Cd) for non-essential ones. Thus, concentration ranges typically spanned over several orders of magnitude. For example, P concentrations ranged from 2007 to 138,133 mg•kg⁻¹ dw, Fe concentrations from 25.9 to 16,909 mg•kg⁻¹ dw and Co from 5.7e⁻² to 13.1 mg•kg⁻¹ dw.

Absolute concentrations of Zn, Cu, Se and Ag were significantly higher in scat samples from Cap Noir colony (500.2 ± 265.0, 309.9 ± 283.1, 39.8 ± 29.3 and 0.93 ± 1.00 mg•kg⁻¹ dw, respectively) than in scat samples from Pointe Suzanne (354.0 ± 210.6, 103.6 ± 110.0, 23.6 ± 18.8 and 0.47 ± 0.65 mg•kg⁻¹ dw, respectively; MWW test *p*-values: 1.5e⁻², 1.2e⁻⁴, 1.5e⁻² and 7.1e⁻³; Table 2, Supplementary Material 1).

The relative proportion of each nutrient within their total mix also showed high inter-sample variations at both colonies (Fig. 1), even if Ca represented the greatest proportion in most. The least variable relative proportions were found for Ca, P, Mg and Sr with coefficients of variation of 0.4, 0.2, 0.8 and 0.7, respectively. For other nutrients, coefficients of variation were above 1, with the highest found for essential trace nutrients Cu, Se, Ni (1.5 for all three) and non-essential trace nutrients Cr and Pb (1.8 and 2.0), and the lowest for Na, K, Zn and As (1.1). Ca and Sr proportions were significantly greater in Pointe Suzanne samples (MWW test *p*-value 4.4e⁻² and 1.7e⁻²) while Mg, Na, Cu, Zn, Se and Ag proportions were significantly greater in Cap Noir samples (MWW test *p*-values: 4.4e⁻², 2.3e⁻², 1.7e⁻³, 1.3e⁻², 3.9e⁻² and 2.2e⁻²; Supplementary Material 1). Cu was seen as the most concentrated micronutrient in few samples from Cap Noir only.

## 3.2. Nutrient typology of Antarctic fur seal scats from the two colonies

We identified different data structure in Cap Noir and Pointe Suzanne based on standard validity measures, sample dendrograms and PCAs biplots, with 3 optimal clusters for scats in Cap Noir and 4 in Pointe

Suzanne. In Cap Noir, cluster 1 included 7 samples (25 % of samples), cluster 2 17 samples (61 %) and cluster 3 4 samples (14 %). In Pointe Suzanne, cluster 1 included 11 samples (35 %), cluster 2 8 samples (26 %), cluster 3 9 samples (29 %) and cluster 4 3 samples (10 %).

In both colonies, there was one cluster significantly enriched in Ca, P and Sr (cluster 1), one cluster significantly enriched in Fe, M, Ni, V and Co (cluster 2 in Cap Noir and 3 in Pointe Suzanne) and one cluster with low concentrations in Mg, Zn and Sr (cluster 3 in Cap Noir and 4 in Pointe Suzanne; Fig. 2). Cluster 1 results for both sites differed significantly in their concentrations of Na, Zn, Mn, Cd, V and As, and cluster 2 from Cap Noir and cluster 3 from Pointe Suzanne differed significantly in their concentrations of Fe, Mn, Ni, V, Cr, As, Co and Pb, with higher concentrations in samples from Pointe Suzanne for these nutrients and singularly higher concentrations in the non-essentials Cr and Pb. In samples from the Mg, Zn and Sr depleted clusters (i.e., cluster 3 in Cap Noir and 4 in Pointe Suzanne; which both contained the fewest samples), nutrient concentrations were not significantly different in either colony despite higher concentrations in Cu, Se and Ag in Cap Noir samples (MWW test *p*-values: 5.7e⁻² for the three nutrients). Cluster 2 samples in Pointe Suzanne had concentrations close to average values for most nutrients analysed, with no equivalent cluster found in Cap Noir.

Results of MWW tests are provided in Supplementary material 1 (for difference in absolute and relative nutrient composition between scats from the two colonies and from different clusters).

## 3.3. Population counts and model intermediate outputs

The minimum pup counts were 500 in Cap Noir and 942 in Pointe Suzanne, and the maximum 698 and 969 (respectively) which resulted in abundance estimates of lactating Antarctic fur seal females of 670 (95 % confidence interval [509–829]) in Cap Noir and 1052 [947–1157] in Pointe Suzanne. The abundance of lactating females in Pointe Suzanne was thus estimated to be 57 % above that in Cap Noir. The average daily metabolic rate (ADMR) of lactating females was 16,569 kJ•day⁻¹
<figure><img src="image_5.png" /><figcaption>**Fig. 1.** Variability in the relative nutrient composition of 59 Antarctic fur seal (Arctocephalus gazella) scats in the Kerguelen Islands (Southern Ocean). Relative proportion of 20 nutrients within the total nutrient mix in each fur seal scat from Cap Noir (left) and Pointe Suzanne (right) colonies are displayed in different panels, with 15 essential nutrients in the four first dark grey panels: Ca, P, Mg, Na, K (top panel), Fe, Zn, Sr (2nd panel), Cu, Mn, Se, Ni (3rd panel), V, As, Co, Mo (4th panel); and 4 non-essential nutrients in the bottom light grey panel: Cd, Cr, Ag and Pb (bottom panel). Note that strontium Sr has no known biological function but has been included with essential nutrients due to its high concentrations in biological tissues. Each vertical bar represents a sample, and the samples have been identically ordered on all panels according to their relative concentration in Fe, i.e. the relative composition of the sample with the highest relative proportion of Fe is shown on the first bar, and the fraction missing to reach 1 on the top panel is shown on the following panels with the scale magnified.</figcaption></figure>

([12,840 - 20,925]) when at sea and 11,633 [9306 - 14,314] $kJ\cdot day^{-1}$ when on land. The estimated average daily ration needed for lactating female fur seals was 2.4 $kg\cdot day^{-1}$ [1.4-4.3], which represents 9 % [5-15] of their body mass. For both colonies, the duration of the breeding and moulting season was 120 [101-139] days, and during this period 75 % [65-85] of faecal nutrient release was estimated to occur at sea and 25 % [15-35] on land.

### 3.4. Faecal nutrient release by lactating fur seal females from the two colonies

In total (i.e., at sea plus on land - $N_{n,t}$ in eq. 10, with total ≈ 75% at sea + 25% on land), faecal nutrient release levels by lactating Antarctic fur seal females from the two colonies of Cap Noir and Pointe Suzanne reached 1045 [912-1178] kg for the most released major nutrient Ca and 30.2 [26.4-34.1] kg for the least released major nutrient K, during the four months of the breeding season. For essential trace nutrients, the most released was Fe with 46.4 [39.8-53.2] kg and the least Mo with 6.3 [5.4-7.2] g released. For non-essential nutrients, Sr was the most released with 3.4 [3.0-3.9] kg and the least Pb with 5.9 [5.2-6.8] g released during the breeding season on and around the Kerguelen Islands. Details of faecal nutrient release at sea and on land for each colony are provided in Table 3. Additional statistics (min, max) are included in Supplementary Material 2 as well as results of our statistical test of difference between colony sites.

At the colony scale, total faecal nutrient release levels by lactating female fur seals were significantly greater at Pointe Suzanne for major nutrients Ca, P, Mg, Na and K, for essential trace nutrients Fe, Mn, Ni, V,

As, Co and Mo and for non-essentials Sr, Cr and Pb, whereas they were significantly greater at Cap Noir for the essential trace nutrient Cu and the non-essential trace nutrient Cd (Fig. 3a). Faecal nutrient release levels were not significantly different in the two colonies for Zn, Se and Ag.

The differences in faecal nutrient release levels between the two fur seal colonies did not only reflect differences in colony abundances (i.e., 57 % more females in Pointe Suzanne than in Cap Noir; Fig. 3b). Faecal nutrient release was higher in Pointe Suzanne for Ca, P, Sr, Mn, Ni, Cr, Pb and to a lesser extent for K, V and As than would be expected based on abundance difference only. The greatest difference was observed for the non-essential nutrients Cr and Pb for which levels were respectively 198 % and 551 % above the difference in colony abundance estimates. On the other hand, faecal nutrient release was higher than would be expected based on abundance difference in Cap Noir for the essential trace nutrients Zn, Cu, Se and the non-essentials Cd and Ag, and to a lesser extent for Mg, Na, Fe, Co and Mo, with the greatest difference observed for Cu (105 %) and Cd (95 %) with significantly higher faecal nutrient release levels than in Pointe Suzanne despite fewer lactating females.

### 4. Discussion

This study provides first quantitative characterisations of the contribution of Antarctic fur seal scats from two Kerguelen Islands colonies to the biological recycling of 20 nutrients - including 15 essential and 5 non-essential nutrients, during their breeding season. We show how the heterogeneity in nutrient composition of individual scats from a single marine predator species can shape the stoichiometry of nutrients
<figure><img src="image_6.png" /><figcaption>**Fig. 2.** Antarctic fur seal (Arctocephalus gazella) scat multi-nutrient typology. Absolute concentrations (in mg per kg dry weight) in Ca, P, Mg, Na, K, Fe, Zn, Sr, Cu, Mn, Se, Ni, V, As, Co, Mo, Cd, Cr, Ag and Pb in clusters of Antarctic fur seal (Arctocephalus gazella) scat samples Cap Noir and Pointe Suzanne colonies (Kerguelen Islands, Southern Ocean). Three clusters were identified in Cap Noir and four clusters were identified in Pointe Suzanne based on a hierarchical clustering (HC) conducted on scat samples' coordinates on the first 5 principal components from a Principal Component Analysis (PCA). The first 16 panels (dark grey) are for essential nutrients and the four last ones (light grey) for the non-essential nutrients. Note that strontium Sr has no known biological function but has been included with the essential nutrients due to its high concentrations in biological tissues. For each nutrient, the horizontal red lines represent mean (dotted line) and median (solid line) values across all scat samples.</figcaption></figure>

released at the scale of a colony. These results provide insights into fur seal-mediated nutrient release patterns on and around the Kerguelen Islands, and their potential contribution to ecosystem dynamics.

## 4.1. Intra- and inter-colony differences in individual scats' composition and typology

We found that relative and absolute nutrient compositions of fur seal scats are highly variable with nutrient concentrations that can span over orders of magnitude. For example, for Fe, the most concentrated sample is approximately 650 times more concentrated than the least concentrated sample. This variability likely reflects that of the relative prey composition of fur seal meals, as different prey species may have different nutrient contents (Chouvelon et al., 2022a). The ranges of concentration are smaller for major nutrients (e.g., K and Na) and greater for both essential (e.g., Cu and Mn) and non-essential (e.g., Ag and Pb) trace nutrients, as observed in a range of potential marine prey (Chouvelon et al., 2022b).

Interestingly, scat composition typology showed similarities between colonies, with three clusters sharing the same distinctive characteristics (e.g., high Ca, P, Sr concentrations or high trace nutrient concentrations). These clusters likely reflect similar intra-colony variability in diets, which may be associated to the observed variability in foraging behaviours and areas targeted by lactating females (Jeanniard-du-Dot et al., 2017a; Lea et al., 2002b; Lea and Dubroca, 2003). For

example, scats enriched in Fe, Cu, Mn, Ni, V, Cr, As, Ag, Pb and Co may reflect the preferential consumption of *Protomyctophum* myctophids (enriched in Fe, Mn, Ni and Co; Gilbert et al., 2025), whereas scats enriched in P, Ca and Sr may reflect the preferential consumption of prey species *Champsocephalus gunnari* (enriched in P and Ca), each being found in the fur seal diet (Cherel et al., 1997; Green and Williams, 1986; Jeanniard-du-Dot, 2015; LLea et al., 2008, 2002a), and possibly in different areas (Bost et al., 2002; Lea et al., 2002a; Lea and Dubroca, 2003).

However, there were also differences in scat compositions between the two colonies that might reflect site-specific foraging strategies (Fig. 4). Cap Noir fur seals forage east of the Kerguelen Islands near the eastern limit of the Kerguelen Plateau and in deep waters off the shelf break (> 500 m deep), while Point Suzanne fur seals forage mainly on the central Plateau southeast of the Kerguelen Islands (< 500 m) (Jeanniard-du-Dot et al., 2017a; Lea et al., 2008; Fig. 4). The relative availability of prey species may differ between these areas (Duhamel et al., 2017; Hindell et al., 2011), which could result in slight or drastic differences in proportion of some prey species in the fur seal meal composition between colonies. For example, some cephalopod and crustacean species have higher concentrations in Cu, Cd, and Ag (Chouvelon et al., 2022a, 2022b; Mille et al., 2018) than fish, so higher concentrations found for these nutrients in Cap Noir clusters may reflect a greater proportion of these taxa in their diet.

In any case, even if we cannot associate each scat type with specific
<caption>**Table 3**</caption>

Faecal nutrient release estimates (in kg, with mean, and 95 % confidence interval in brackets) by lactating female Antarctic fur seals (*Arctocephalus gazella*) from the two colonies of Cap Noir and Pointe Suzanne (Kerguelen Islands, Southern Ocean), during the four months of their breeding and moulting period (Austral summer). Estimated levels result from a bioenergetic model set up with Monte-Carlo simulations and set up with a dataset of 59 scats collected on the two colonies in 2021–2022. Faecal nutrient release levels in bold were significantly different between colonies according to a comparative statistical test developed to cope with large dimension of our results (see 2.4.6). The four last nutrients in the right of the table are considered as non-essential and potentially toxic nutrients (note that strontium Sr has no any known biological function but has been included with essential nutrients due to its high concentrations in biological tissues). Note that a multiplier to be applied to the faecal nutrient release estimates is given below the nutrient for Mn, Se, Ni, V, As, Co, Mo, Cd, Cr, Ag and Pb. Additional statistics (min and max) and results of the statistical tests are provided in Supplementary Material 2.

<table><thead><tr><th>Colony</th><th>Release level</th><th>Ca</th><th>P</th><th>Mg</th><th>Na</th><th>K</th><th>Fe</th><th>Zn</th><th>Sr</th><th>Cu</th><th>Mn</th><th>Se</th><th>Ni</th><th>V</th><th>As</th><th>Co</th><th>Mo</th><th>Cd</th><th>Cr</th><th>Ag</th><th>Pb</th></tr><tr><th></th><th></th><th></th><th></th><th></th><th></th><th></th><th></th><th></th><th></th><th></th><th>*1e<sup>-1</sup></th><th>*1e<sup>-1</sup></th><th>*1e<sup>-1</sup></th><th>*1e<sup>-2</sup></th><th>*1e<sup>-2</sup></th><th>*1e<sup>-2</sup></th><th>*1e<sup>-3</sup></th><th>*1e<sup>-2</sup></th><th>*1e<sup>-2</sup></th><th>*1e<sup>-3</sup></th><th>*1e<sup>-3</sup></th></tr></thead><tbody><tr><td rowspan="3">Cap Noir</td><td>at sea</td><td>247<br>[181;<br>313]</td><td>157<br>[116;<br>198]</td><td>39.1<br>[29.5;<br>48.8]</td><td>26.0<br>[19.7;<br>32.5]</td><td>8.3<br>[6.3;<br>10.3]</td><td>14.3<br>[10.5;<br>18.2]</td><td>1.9<br>[1.4;<br>2.4]</td><td>0.8<br>[0.6;<br>1.0]</td><td>1.2<br>[0.9;<br>1.5]</td><td>2.8<br>[2.1;<br>3.6]</td><td>1.5<br>[1.1;<br>1.9]</td><td>0.5<br>[0.4;<br>0.7]</td><td>1.7<br>[1.3;<br>2.2]</td><td>1.3<br>[1.0;<br>1.6]</td><td>1.2<br>[0.9;<br>1.5]</td><td>2.0<br>[1.5;<br>2.6]</td><td>6.0<br>[4.2;<br>7.8]</td><td>1.2<br>[0.9;<br>1.5]</td><td>3.5<br>[2.6;<br>4.5]</td><td>0.6<br>[0.4;<br>0.7]</td></tr><tr><td>on land</td><td>82 [60;<br>104]</td><td>52 [38;<br>66]</td><td>13.0<br>[9.8;<br>16.2]</td><td>8.6<br>[6.5;<br>10.8]</td><td>2.7<br>[2.1;<br>3.4]</td><td>4.7<br>[3.5;<br>6.0]</td><td>0.6<br>[0.5;<br>0.8]</td><td>0.3<br>[0.2;<br>0.3]</td><td>0.4<br>[0.3;<br>0.5]</td><td>0.9<br>[0.7;<br>1.2]</td><td>0.5<br>[0.4;<br>0.6]</td><td>0.2<br>[0.1;<br>0.2]</td><td>0.6<br>[0.4;<br>0.7]</td><td>0.4<br>[0.3;<br>0.5]</td><td>0.4<br>[0.3;<br>0.5]</td><td>0.7<br>[0.5;<br>0.8]</td><td>2.0<br>[1.4;<br>2.6]</td><td>0.4<br>[0.3;<br>0.5]</td><td>1.2<br>[0.9;<br>1.5]</td><td>0.2<br>[0.1;<br>0.2]</td></tr><tr><td>at sea + on land</td><td>328<br>[241;<br>417]</td><td>209<br>[154;<br>264]</td><td>52.1<br>[39.4;<br>64.9]</td><td>34.7<br>[26.2;<br>43.2]</td><td>11.0<br>[8.3;<br>13.7]</td><td>19.0<br>[14.0;<br>24.2]</td><td>2.5<br>[1.9;<br>3.2]</td><td>1.0<br>[0.8;<br>1.3]</td><td>1.6<br>[1.2;<br>2.0]</td><td>3.8<br>[2.8;<br>4.8]</td><td>2.0<br>[1.5;<br>2.5]</td><td>0.7<br>[0.5;<br>0.9]</td><td>2.3<br>[1.7;<br>2.9]</td><td>1.6<br>[1.2;<br>2.0]</td><td>1.6<br>[1.2;<br>2.0]</td><td>2.7<br>[2.0;<br>3.4]</td><td>8.0<br>[5.6;<br>8.9]</td><td>1.6<br>[1.2;<br>2.0]</td><td>4.7<br>[3.5;<br>6.0]</td><td>0.7<br>[0.5;<br>0.9]</td></tr><tr><td rowspan="3">Pointe Suzanne</td><td>at sea</td><td>538<br>[473;<br>607]</td><td>315<br>[277;<br>356]</td><td>54.0<br>[47.9;<br>60.2]</td><td>37.9<br>[33.7;<br>42.3]</td><td>14.4<br>[12.8;<br>16.1]</td><td>20.6<br>[17.8;<br>23.6]</td><td>2.1<br>[1.9;<br>2.4]</td><td>1.8<br>[1.6;<br>2.0]</td><td>0.6<br>[0.5;<br>0.7]</td><td>6.4<br>[5.5;<br>7.3]</td><td>1.1<br>[1.2;<br>1.3]</td><td>3.3<br>[2.8;<br>3.7]</td><td>2.4<br>[2.2;<br>2.7]</td><td>1.6<br>[1.4;<br>2.7]</td><td>2.7<br>[2.4;<br>3.0]</td><td>3.7<br>[3.3;<br>4.2]</td><td>4.1<br>[3.6;<br>4.7]</td><td>2.8<br>[2.4;<br>3.2]</td><td>3.9<br>[3.3;<br>4.5]</td></tr><tr><td>on land</td><td>178<br>[156;<br>201]</td><td>104<br>[92;<br>118]</td><td>17.9<br>[15.9;<br>20.0]</td><td>12.6<br>[11.1;<br>14.1]</td><td>4.8<br>[4.2;<br>5.3]</td><td>6.8<br>[5.9;<br>7.8]</td><td>0.7<br>[0.6;<br>0.8]</td><td>0.6<br>[0.5;<br>0.7]</td><td>0.2<br>[0.2;<br>0.2]</td><td>2.1<br>[1.8;<br>2.4]</td><td>0.5<br>[0.4;<br>0.5]</td><td>0.4<br>[0.3;<br>0.4]</td><td>1.1<br>[0.9;<br>1.2]</td><td>0.8<br>[0.7;<br>0.9]</td><td>0.9<br>[0.5;<br>0.6]</td><td>0.9<br>[0.8;<br>1.0]</td><td>1.2<br>[1.1;<br>1.4]</td><td>1.4<br>[1.2;<br>1.6]</td><td>0.9<br>[0.8;<br>1.1]</td><td>1.3<br>[1.1;<br>1.5]</td></tr><tr><td>at sea + on land</td><td>716<br>[630;<br>807]</td><td>419<br>[369;<br>473]</td><td>71.9<br>[63.9;<br>80.1]</td><td>50.5<br>[44.9;<br>56.3]</td><td>19.2<br>[17.0;<br>21.5]</td><td>27.4<br>[23.7;<br>31.4]</td><td>2.8<br>[2.5;<br>3.2]</td><td>2.4<br>[2.1;<br>2.7]</td><td>0.8<br>[0.7;<br>0.9]</td><td>8.5<br>[7.3;<br>9.7]</td><td>1.9<br>[1.7;<br>2.1]</td><td>1.5<br>[1.3;<br>1.7]</td><td>4.3<br>[3.7;<br>4.9]</td><td>2.3<br>[2.9;<br>3.6]</td><td>2.2<br>[1.9;<br>2.5]</td><td>3.6<br>[3.2;<br>4.0]</td><td>5.0<br>[4.3;<br>5.6]</td><td>5.5<br>[4.8;<br>6.3]</td><td>3.7<br>[3.2;<br>4.3]</td><td>5.2<br>[4.5;<br>6.0]</td></tr><tr><td rowspan="3">Cap Noir + Pointe Suzanne</td><td>at sea</td><td>785<br>[685;<br>886]</td><td>472<br>[411;<br>532]</td><td>93.1<br>[80.7;<br>105.5]</td><td>64.0<br>[55.6;<br>2.4]</td><td>22.7<br>[19.8;<br>25.6]</td><td>34.9<br>[29.9;<br>40.0]</td><td>4.0<br>[3.5;<br>4.6]</td><td>2.6<br>[2.3;<br>2.9]</td><td>1.8<br>[1.5;<br>2.1]</td><td>9.2<br>[8.0;<br>10.5]</td><td>2.9<br>[2.4;<br>3.4]</td><td>1.7<br>[1.4;<br>1.9]</td><td>5.0<br>[4.3;<br>5.7]</td><td>3.7<br>[3.2;<br>4.2]</td><td>2.8<br>[2.4;<br>3.2]</td><td>4.7<br>[4.1;<br>5.4]</td><td>9.7<br>[7.9;<br>11.6]</td><td>5.3<br>[4.6;<br>6.0]</td><td>6.3<br>[5.3;<br>7.4]</td><td>4.5<br>[3.9;<br>5.1]</td></tr><tr><td>on land</td><td>260<br>[227;<br>294]</td><td>156<br>[136;<br>177]</td><td>30.9<br>[26.7;<br>35.0]</td><td>21.2<br>[18.4;<br>24.0]</td><td>7.5<br>[6.6;<br>8.5]</td><td>11.6<br>[9.9;<br>13.3]</td><td>1.3<br>[1.1;<br>1.5]</td><td>0.9<br>[0.7;<br>1.0]</td><td>0.6<br>[0.5;<br>0.7]</td><td>3.1<br>[2.7;<br>3.5]</td><td>1.0<br>[0.8;<br>1.1]</td><td>0.6<br>[0.5;<br>0.6]</td><td>1.7<br>[1.4;<br>1.9]</td><td>1.2<br>[1.1;<br>1.4]</td><td>0.9<br>[0.8;<br>1.1]</td><td>0.2<br>[0.1;<br>0.2]</td><td>3.2<br>[2.6;<br>3.9]</td><td>1.8<br>[1.5;<br>2.0]</td><td>2.1<br>[1.8;<br>2.5]</td><td>1.5<br>[1.3;<br>1.7]</td></tr><tr><td>at sea + on land</td><td>1045<br>[912;<br>1178]</td><td>628<br>[548;<br>710]</td><td>124<br>[107;<br>140]</td><td>85.2<br>[73.9;<br>96.4]</td><td>30.2<br>[26.4;<br>34.1]</td><td>46.4<br>[39.8;<br>53.2]</td><td>5.4<br>[4.6;<br>6.1]</td><td>3.4<br>[3.0;<br>3.9]</td><td>2.4<br>[2.0;<br>2.8]</td><td>12.3<br>[10.7;<br>14.0]</td><td>3.9<br>[3.3;<br>4.5]</td><td>2.2<br>[1.9;<br>2.5]</td><td>6.6<br>[5.7;<br>7.6]</td><td>4.9<br>[4.3;<br>5.5]</td><td>3.7<br>[3.2;<br>4.3]</td><td>6.3<br>[5.4;<br>7.2]</td><td>12.9<br>[10.5;<br>15.5]</td><td>7.1<br>[6.2;<br>8.0]</td><td>8.4<br>[7.0;<br>9.8]</td><td>5.9<br>[5.2;<br>6.8]</td></tr></tbody></table>

diets or prey species, our results highlight how individual differences are a source of variation in these processes despite being commonly overlooked (McInturf et al., 2019). They also provide valuable information on Antarctic fur seal contributions to nutrient recycling on and around the Kerguelen Islands at individual and colony levels.

## 4.2. Inter-colony differences in total faecal nutrient release

Colony faecal nutrient release levels (i.e., $N_{n,t}$ in eq. 10, all colony lactating females over the breeding period) in Cap Noir and Pointe Suzanne reflected differences in abundance of lactating female fur seals, as well as colony differences in individual scat compositions. Indeed, lactating females were 1.6 times (57 %) more numerous at Pointe Suzanne colony than at Cap Noir, and yet, females at Cap Noir released 1.9 and 1.6 times more Cu and Cd (respectively) or similar levels of Zn, Se and Ag than females at Pointe Suzanne. In addition, females at Pointe Suzanne released around twice as much Ca, P, Sr, Mn, Ni and As, 3.6 times more Cr and 7.4 times more Pb than females at Cap Noir. It is interesting to note that these colony differences are observed for both essential and non-essential nutrients, with important differences for the four potentially toxic nutrients Ag and Cd (more released in Cap Noir) and Cr and Pb (more released in Pointe Suzanne) (Fig. 3). These transfers of pollutants may impact the recipient ecosystem, and these results suggest that the role of marine predators in nutrient dynamics should not be approached solely with a focus on essential nutrients but also as a vector of contamination (Grant et al., 2024).

Overall, these inter-colony differences suggest that estimating large-scale predator nutrient release based on averages, whether of diet and prey compositions (e.g., Gilbert et al., 2023a, 2023b; Lavery et al., 2010; Roman and McCarthy, 2010) or of faecal nutrient contents (e.g., Lavery

et al., 2015, 2014), likely overlooks important fine-scale spatial variability in the contribution of a given species. Population variability may not be important if the focus is on large-scale estimates only and not population relative contributions. However, our results suggest that small-scale variations in diets, prey or scat composition of different populations should be considered in any approach that focuses on fine-scale spatial patterns of nutrient release, whether quantitative (amounts released) or qualitative (relative composition of nutrient cocktails released), such as the present study.

In the Kerguelen Islands, the present study is – to date, the first to provide quantitative information on the contribution of a marine predator species to biogeochemical nutrient recycling, so the contrasts observed in both the nutrient content of scats and the total faecal nutrient release levels by two colonies are *per se* informative. Yet, to come closer to assessing the ecological significance of such contributions (i.e., how do they affect the nutrient background of the recipient ecosystem? are they likely to have a fertilising effect?), these contributions need to be considered in the context of the recipient ecosystems (Subalusky and Post, 2019).

## 4.3. Antarctic fur seal faecal nutrient release at sea

We have shown that the faecal nutrient release at sea by lactating fur seals during a breeding season ($N_{n,sea}$ in eq. 9) was greater for Pointe Suzanne colony than from Cap Noir colony, for most nutrients (including Fe and Mn). There is limited overlap between at-sea foraging areas of fur seals breeding at Cap Noir or at Pointe Suzanne (Fig. 4), so animals from the two colonies are unlikely to release faecal nutrients in the same areas around the Kerguelen Islands. Interestingly, the two foraging areas correspond relatively well to two water masses with
<figure><img src="image_7.png" /><figcaption>b</figcaption></figure>

<figure><img src="image_8.png" /></figure>

**Fig. 3.** Nutrient release by lactating female Antarctic fur seals (*Arctocephalus gazella*) from two colonies of the Kerguelen Islands (Southern Ocean). (a) Absolute levels of nutrients Ca, P, Mg, Na, K, Fe, Zn, Sr, Cu, Mn, Se, Ni, V, As, Co, Mo, Cd, Cr, Ag and Pb released in fur seal scats from lactating females from Cap Noir and Pointe Suzanne colonies during the four months of the breeding and moulting season as estimated using a bioenergetic model and a scat composition dataset; red stars indicate a significant difference between nutrient release levels in the two colonies, and (b) percentage of deviation in nutrient release level from Cap Noir to Pointe Suzanne colony where zero is set at the percentage of difference in the abundance of breeding females (57 %), i.e., if colony nutrient release levels reflected only difference in abundance all bars would be at zero, a negative percentage of change indicates nutrient release is higher in Cap Noir despite lower animal abundance and a percentage of change above zero indicates nutrient release is higher in Pointe Suzanne than would be expected solely based on colony abundance difference. The first 16 nutrients (dark grey panels in (a), in bold black in (b)) are essential nutrients and the four last ones (light grey panels in (a), in bold grey in (b)) are non-essential nutrients. Note that strontium Sr has no known biological function but has been included with the essential nutrients due to its high concentrations in biological tissues.

different nutrient and productivity dynamics (Bowie et al., 2015; Koubbi et al., 2016). The central Plateau southeast of Kerguelen - where fur seals from Pointe Suzanne preferentially forage (Fig. 4), shows higher Fe and Mn nutrient concentrations and productivity regimes than the area off the eastern Plateau, identified by Bowie et al. (2015) as a *quasi-stationary, bathymetrically trapped recirculation feature* associated with the Polar Front, and termed an *offshore plume* (referred to as such hereafter) - where fur seals from Cap Noir preferentially forage (Bowie et al., 2015; van Der Merwe et al., 2015). The faecal nutrient enrichment mediated by fur seals at sea may therefore be relatively greater in the nutrient-

poorer offshore plume than on the nutrient-richer central Plateau because of their different nutrient background, despite colony release levels (N<sub>n.t.sea</sub> in eq. 9) being greater in the latter, for most nutrients. In addition, primary producer and microbial communities might differ between these two foraging areas (Hunt et al., 2021), so they could respond differently to a change in their local biochemical environment (Moore et al., 2007), including from fur seal scat enrichment.

However, the scale of colony faecal nutrient releases (N<sub>n.t.sea</sub>) may not be the most appropriate to infer the ecosystem response to potential fertilisation by Antarctic fur seals around the Kerguelen Islands. At sea,
<figure><img src="image_9.png" /><figcaption>**Fig. 4.** At-sea tracks of lactating female Antarctic fur seals (*Arctocephalus gazella*) from two colonies of the Kerguelen Islands (Southern Ocean). Animals were equipped at Cap Noir in 1998, 1999, 2000 (in black) and Pointe Suzanne in 2007, 2010, 2012, 2022 (in purple). Data published in Guinet et al. (2001), Jeanniard-du-Dot et al. (2017b), Lea et al. (2002b, 2008), Lea and Dubroca (2003) and Chevallay et al. (2024) for years 1998, 1999, 2000, 2007, 2012 and 2022; 2010 data were not published. Blue gradient background indicates bathymetry, the yellow dotted line and the red dashed line indicate respectively the approximate locations of the subantarctic polar front (SAF) and the polar front (PF), and orange full circles indicates sampling stations associated to water masses with different biochemical characteristics (an offshore plume and central Kerguelen Plateau) in Bowie et al. (2015).</figcaption></figure>

fur seal faecal nutrient inputs are very local (one scat), diffuse (animals do not congregate), and likely transient. Major unknowns remain, such as the biochemical forms of nutrients released (e.g., dissolved or particulate) and their dissolution and retention rates in surface waters. Yet, comparing total nutrient concentrations in scats ($x_{n,t}$ in eq. 5) with the total nutrient concentrations measured in the upper mixed layer (i.e., dissolved + particulate), or with the estimated biological nutrient recycling rates by microbial and mesozooplanctonic communities at oceanographic stations near the foraging areas (Fig. 4), may be an interesting thought experiment to get a better idea of the fur-seal mediated relative nutrient enrichment. For example, a $m^2$ of the mixed layer contained on average ≈ 934 µmol of total iron on the central Plateau and ≈ 96 µmol in the offshore plume (Bowie et al., 2015) (Fig. 5). In comparison, a fur seal scat contained 10 to 993 µmol of Fe (average Fe content of samples with concentrations below the 5 and 95 percentiles, respectively). Immediately upon release, a scat could thus increase the total iron in one $m^2$ of the mixed layer by ≈ 1 to 1035 % depending on the scat iron concentration range and the location (Fig. 5). If only 5 % of the total iron contained in scat dissolves and becomes bioavailable, the relative enrichment ranges between 0.05 and 52 %, which could still be significant for a single, punctual event. On the other hand, for one fur seal scat, concentrations of total faecal Fe could reach 10 to 993 $µmol·m^{-2}$ on the Plateau and in the offshore plume; or 0.5 to 49.7 $µmol·m^{-2}$ if only 5 % dissolves and become bioavailable. In comparison, each day the microbial and mesozooplanktonic communities regenerate on average ≈ 4.5$e^{-2}$ $µmol·Fe·m^{-2}$ on the Plateau and 2.7$e^{-2}$ $µmol·Fe·m^{-2}$ in the offshore plume (Bowie et al., 2015).

These simplistic calculations suggest fur seals could be locally important contributors to the biological recycling of iron when they defecate at sea, despite the non-limiting conditions observed during the high productivity season. In the Kerguelen area and during the Austral summer, iron is most likely not the primary limiting nutrient (Blain

et al., 2015). However, we have shown that fur seal scats contain a complex mix of nutrients, including major nutrients, notably phosphorus, that may become limiting in an area repleted with micro-nutrients. They are also likely to contain nitrogen (Alba-González et al., 2022; Roman et al., 2016; Wing et al., 2021), even though it was not analysed due to analytical constraints. Thus, a positive response of primary producers or microbes to fur seal scat release should not be excluded despite of the singular biogeochemical context of the Kerguelen area. Indeed, incubation experiments with seabird guano fertilisation in waters of different nutrient regimes have shown a boost in productivity both in area depleted or repleted with micronutrients (Shatova et al., 2016). In addition, the patchy and transient scat-mediated multi-nutrient enrichment may influence heterogeneity in the environment nutrient background, thereby increasing fine-scale habitat complexity, and lower trophic level community responses (patchiness, productivity, diversity, species assemblages) (Kovalenko et al., 2012; McInturf et al., 2019; Mouillot et al., 2013; van der Plas, 2019), depending on their affinity with specific nutrients (Shatova et al., 2017).

Finally, Antarctic fur seals are also highly mobile at sea, and are as such involved in spatial nutrient transfers. Lactating females can travel hundreds of kilometres on a single foraging trip with foraging areas reaching 2500 $km^2$ for an individual fur seal and 40,000 $km^2$ for a colony (Jeanniard-du-Dot et al., 2017a; Lea et al., 2008, 2006). They can thus transport nutrients against abiotic forces such as wind and currents, and from and to places with different nutrient characteristics, which adds another level of complexity to the local ecosystem heterogeneity they may mediate (McInturf et al., 2019; Subalusky and Post, 2019). Antarctic fur seal may also mediate vertical nutrient transfers within the water column. While their foraging dives are relatively shallow (≈ 20–50 m) (Jeanniard-du-Dot et al., 2017a; Lea et al., 2002b), they mostly feed on mesopelagic prey (Cherel et al., 1997; Jeanniard-du-Dot
<figure><img src="image_10.png" /><figcaption>**Fig. 5.** Relative iron enrichment following one Antarctic fur seal (Arctocephalus gazella) defecation in surface waters around the Kerguelen Islands (Southern Ocean): a thought experiment. The upper part of the scheme illustrates the average background conditions in the mixed layer in two different water masses (offshore plume on the left, central Kerguelen Plateau on the right) based on results of Bowie et al. (2015). The lower part of the scheme illustrates the potential relative enrichment in total iron caused in the mixed layer by 3 hypothetical fur seal scats at the immediate time of release, with the background iron content (dissolved + particulate) taken as the reference (i.e. 100 %). The median scat calculation uses the overall median dry mass and iron concentration of 59 fur seal scats collected in the Kerguelen Islands, the low and high iron concentration scat calculations use the average dry mass and iron concentration of samples with iron concentrations < 5 % and ≥ 95 % quantile values for iron concentration in the dataset, respectively. Iron content in one scat is given in mass concentration, mass and moles, and the calculation used an iron molar concentration of 55.845 g·mol⁻¹.</figcaption></figure>

et al., 2017a; Lea et al., 2002a) which migrate in the upper water column at night (Bost et al., 2002). The nutrients released in their scats may therefore be in part allochthonous, i.e., originating from outside the surface water layer where they are released (Lavery et al., 2010).

## 4.4. Antarctic fur seal-mediated nutrient release on land

On land, fur seal faecal nutrient deposition is concentrated on limited coastal surface areas where animals gather in dense colonies during a specific time period. In our case, fur seal colonies occupy ≈ 48,000 m² at Cap Noir and ≈ 55,000 m² at Pointe Suzanne at mid breeding season. This is ≈ 1 million times smaller than a potential colony influence area at sea as defined by their foraging range. In addition - and unlike at sea, nutrient dispersion remains limited on land even if abiotic conditions (wind, precipitation) can increase scats spatial footprints (Bokhorst et al., 2019b). As such, this fur seal-mediated nutrient enrichment can accumulate during their breeding on land and likely persists beyond fur seals departure, as seen for mammal grazers (Abbas et al., 2012; Barthelemy et al., 2018; Tabeni et al., 2022). This intense pulse of allochthonous nutrient input can thus impact primary producers of the terrestrial trophic web.

Major nutrients such as N, P, K, Ca, Mg and Na are more limiting for terrestrial plant production than trace nutrients (Uchida and Silva, 2000). In this study, we did not quantify N fur seal input due to analytical constraints. However, fur-seal mediated P levels released on land (N<sub>n.t.land</sub> in eq. 8) reached ≈ 52 [38–66] kg at Cap Noir and 104 [92–118] kg at Pointe Suzanne over their breeding season. Assuming a homogeneous release by fur seals over the colony areas (and no drain from rainwater), fur seals would deposit ≈ 0.8 to 1.4 g·P·m⁻² at Cap Noir and ≈ 1.7 to 2.1 g·P·m⁻² at Pointe Suzanne, which is in the range of phosphorus-based fertilisers used in agricultural production

worldwide (0.1 to over 4 g·P·m⁻²; Lu and Tian, 2017). This further suggests that Antarctic fur seals quantitatively shape patterns of productivity at their colony site. Beyond P, Antarctic fur seal scats also contain high Ca, Na, Mg and K concentrations, and could as such provide a complete fertiliser formula for terrestrial ecosystems. In addition, pinnipeds mainly excrete N in urine (Keiver et al., 1984; Ronald et al., 1984), so scats provide only a partial picture of fur seal contribution to biological nutrient recycling in terrestrial ecosystems.

Micro-nutrients are also essential for most terrestrial life forms (Hu et al., 2021; Uchida and Silva, 2000), and low concentrations can provoke deficiencies and limit plant productivity (He et al., 2005; Hu et al., 2021; Uchida and Silva, 2000). On land, the capacity of the ecosystem to recycle nutrients from organic matter such as faeces is mainly determined by decomposers, from bacteria to invertebrates, that subsequently make them available to primary producers (Coleman et al., 1983; Dubeux et al., 2007; Thies and Grossman, 2006). However, soil microorganisms and plant communities can respond to micro-nutrients supplies by changes in their biomass, activity and community structure, whether positive or negative (if concentrations are too high) (He et al., 2005; Mooshammer et al., 2014; Salminen et al., 2001; Thies and Grossman, 2006). Because each species has specific nutrient requirements and metabolism, their response to a given macro-nutrient enrichment may differ according to their needs and capabilities if the concurrent supply of micro-nutrients varies (Monk and Schmitz, 2022; Scherer-Lorenzen et al., 2022). Thus, the micro-nutrient fraction of marine predator inputs on land should not be neglected, as the effects of nutrient deposition by fur seals may extend beyond the productivity aspects of macro-nutrient inputs to potential community structuring by both macro and micro-nutrients.

Our results finally highlighted a difference in intensity and quality of faecal nutrient deposition between Cap Noir and Pointe Suzanne, which
could lead to differences in local primary productivity and community structure. However, these characteristics are largely determined by abiotic factors such as exposure, slope, wind and rain regimes (Aiba et al., 2012; Kimberley et al., 2014; Kreft and Jetz, 2007; Wang et al., 2023) so these differences between Cap Noir and Pointe Suzanne alone may imply a different response of the ecosystem to similar type and quantity of fertilisers. It is also worth noting the significant differences in release levels of some non-essential nutrients, particularly Pb and Cr (Kumar and Prasad, 2018; Nagajyoti et al., 2010). Pointe Suzanne terrestrial ecosystem may receive ≈ 3 times more Cr and 6 times more Pb per square meter and per year (≈ 249 µg and 24 µg, respectively) than Cap Noir (≈ 81 µg and 4 µg). Pb concentrations in fur seal scats remain one to five orders of magnitude lower than concentrations ranges in most agricultural amendments, while Cr concentrations come close (Nagajyoti et al., 2010). They are both highly toxic, even though their toxicity depends on their biochemical form and the ecosystem background conditions (e.g., pH, temperature, soil aeration, plant competition, etc.; Nagajyoti et al., 2010). We therefore suggest that the influence of fur seal-mediated nutrient deposition on their colony sites should be investigated considering both essential and non-essential nutrients (Santamans et al., 2017).

### 4.5. Limits and conclusion

Although we provide the first estimates of nutrient release by Antarctic fur seals on and around Kerguelen, they are likely underestimated. First, we only considered lactating females, without taking into account males and subadults. We did not consider nutrients deposited by pups on land following milk consumption either, transferred from the marine environment via the mother. However, the spatial differences we found are still indicative of the true relative release patterns, assuming an equivalent population structure for the two colonies.

Second, our results provide a snapshot of scat-mediated nutrient release patterns by fur seals. Indeed, oceanographic conditions vary both spatially and temporally (seasonally and annually) (Bowie et al., 2015; D'Ovidio et al., 2015). Fur seals can switch prey depending on what is available and accessible in their environment at a given time (Lea et al., 2002a; Lea and Dubroca, 2003). Thus, the diet of Antarctic fur seals is likely to change within and between seasons (Arthur et al., 2015; Guinet et al., 2001; Lea et al., 2002a), which may translate into shifts in fur seal faecal nutrient release patterns. At sea, such changes may also apply to the spatial transfers they mediate. On land, fur seals are limited to their colony area so nutrient deposition from scats should not greatly vary spatially, but temporal changes in the quality of fur seal faecal nutrient input could influence the ecosystem structure and dynamics.

Finally, we only estimated scat-mediated nutrient release for two extensively studied Antarctic fur seal colonies whereas there is other predator species, colonies and predator-mediated nutrient transfer pathways. For example, at Pointe Suzanne, the impact of Antarctic fur seals on the terrestrial ecosystem is combined with that of gentoo penguins (*Pygoscelis papua*) and elephant seals. In terrestrial ecosystems, the additional supply of carcasses, fur and feathers is another pathway for nutrient transfer (Smith, 2008). All these species also release nutrients at sea, where the contribution of other strictly marine predators adds up (e. g., cetaceans). Each species has different distribution, phenology, physiology, diet and behaviour (Koubbi et al., 2016; Thiebot et al., 2012; Thiers et al., 2017), which is likely to add another level of complexity to their contribution to local nutrient dynamics. This study thus provides a first insight into the role of a marine predator in biological nutrient recycling processes in the unique area of the Kerguelen Plateau, and lays the groundwork for further assessment of their contributions.

### CRediT authorship contribution statement

Lola Gilbert: Writing – original draft, Visualization, Methodology,

Investigation, Formal analysis, Data curation, Conceptualization. **Jérôme Spitz:** Writing – review & editing, Visualization, Investigation, Conceptualization. **Mathilde Chevallay:** Writing – review & editing, Visualization. **Tiphaine Jeanniard-du-Dot:** Writing – review & editing, Visualization, Methodology, Investigation, Conceptualization.

### Declaration of Generative AI and AI-assisted technologies in the writing process

During the preparation of this work the corresponding author used DeepL Write in order to improve language and readability. After using this tool/service, the authors reviewed and edited the content as needed and take full responsibility for the content of the publication.

### Funding

This work was supported by La Rochelle University through a PhD grant (2020-2023).

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that influenced the work reported in this paper.

### Acknowledgments

We thank the French Polar Institute (Institut Paul Emile Victor or IPEV) and especially the program 109 ("ORNITHOECO") for their support in collecting the faecal samples in Kerguelen, and the people who collected the samples on the field. We also thank the "Plateforme Analyses Élémentaires" of the LIENS (Littoral ENvironment et Sociétés; UMR 7266 CNRS - La Rochelle Université) for their technical support in the nutrient analysis, and especially Carine Churlaud and Maud Brault-Favrou for their help and kindness. We thank Tiphaine Chouvelon for her helpful advices in treating the composition data.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.scitotenv.2025.179195.

### Data availability

Data of Antarctic fur seal scat nutrient composition are available in InDoRes (Inventaire des Données de la Recherche en Environnement et Sociétés) at doi:10.48579/PRO/9PR5YU. Code to reproduce the full analysis in R is available on Github (https://github.com/Lola-san/Agazella.nutrient.release.Ker.git).

### References

Abbas, F., Merlet, J., Morellet, N., Verheyden, H., Hewison, A.J.M., Cargnelutti, B., Angibault, J.M., Picot, D., Rames, J.L., Lourtet, B., Aulagnier, S., Daufresne, T., 2012. Roe deer may markedly alter forest nitrogen and phosphorus budgets across Europe. Oikos 121, 1271-1278. https://doi.org/10.1111/j.1600-0706.2011.20103.x.

Aiba, M., Takafumi, H., Hiura, T., 2012. Interspecific differences in determinants of plant species distribution and the relationships with functional traits. J. Ecol. 100, 950-957. https://doi.org/10.1111/j.1365-2745.2012.01959.x.

Alba-González, P., Álvarez-Salgado, X.A., Cobelo-García, A., Kaal, J., Teira, E., 2022. Faeces of marine birds and mammals as substrates for microbial plankton communities. Mar. Environ. Res. 174, 105560. https://doi.org/10.1016/j.marenvres.2022.105560.

Arnould, J.P.Y., Boyd, I.L., Speakman, J.R., 1996. The relationship between foraging behaviour and energy expenditure in Antarctic fur seals. J. Zool. 239, 769-782. https://doi.org/10.1111/j.1469-7998.1996.tb05477.x.

Arthur, B., Hindell, M., Bester, M., Trathan, P., Jonsen, I., Staniland, I., Oosthuizen, W.C., Wege, M., Lea, M.A., 2015. Return customers: foraging site fidelity and the effect of environmental variability in wide-ranging antarctic fur seals. PLoS One 10, 1-19. https://doi.org/10.1371/journal.pone.0120888.
Assent, I., 2012. Clustering high dimensional data. Wiley Interdiscip. Rev. Data Min. Knowl. Discov. 2, 340–350. https://doi.org/10.1002/widm.1062.

Atkinson, C.L., Cappas, K.A., Rugenski, A.T., Vanni, M.J., 2017. Consumer-driven nutrient dynamics in freshwater ecosystems: from individuals to ecosystems. Biol. Rev. 92, 2003–2023. https://doi.org/10.1111/brv.12318.

Ball, B.A., Tellez, C.R., Virginia, R.A., 2015. Penguin activity influences soil biogeochemistry and soil respiration in rookeries on Ross Island. Antarctica. Polar Biol. 38, 1357–1368. https://doi.org/10.1007/s00300-015-1699-7.

Ballantyne IV, F., Menge, D.N.L., Ostling, A., Hosseini, P., 2008. Nutrient recycling affects autotroph and ecosystem stoichiometry. Am. Nat. 171, 511–523. https://doi.org/10.1086/528967.

Barlow, J., Kahru, M., Mitchell, B.G., 2008. Cetacean biomass, prey consumption, and primary production requirements in the California current ecosystem. Mar. Ecol. Prog. Ser. 371, 285–295. https://doi.org/10.3354/meps07695.

Barthelemy, H., Stark, S., Michelsen, A., Olofsson, J., 2018. Urine is an important nitrogen source for plants irrespective of vegetation composition in an Arctic tundra: Insights from a 15N-enriched urea tracer experiment. J. Ecol. 106, 367–378. https://doi.org/10.1111/1365-2745.12820.

Belyaev, O., Sparaventi, E., Navarro, G., Rodríguez-Romero, A., Tovar-Sanchez, A., 2023. The contribution of penguin guano to the Southern Ocean iron pool. Nat. Commun. 14. https://doi.org/10.1038/s41467-023-37132-5.

Blenkwick, C.E., Gunn, R.L., Corre, M. Le, Carr, P., Graham, N.A.J., 2021. Rat eradication restores nutrient subsidies from seabirds across terrestrial and marine ecosystems. Curr. Biol. 31, 1–8. https://doi.org/10.1016/j.cub.2021.03.104.

Blenkwick, C.E., Carr, P., Wilson, S.K., Graham, N.A.J., 2022. Seabird diversity and biomass enhance cross-ecosystem nutrient subsidies. Proc. R. Soc. B Biol. Sci. 289. https://doi.org/10.1098/rspb.2022.0195.

Bester, M.N., Ryan, P.G., Dyer, B.M., 2003. Population numbers of fur seals at Prince Edward Island. Southern Ocean. African J. Mar. Sci. 25, 549–554. https://doi.org/10.2989/1814230209504044.

Bestley, S., Ropert-Coudert, Y., Bengtson Nash, S., Brooks, C.M., Cotté, C., Dewar, M., Friedlaender, A.S., Jackson, J.A., Labrousse, S., Lother, A.D., McMahon, C.R., Phillips, R.A., Pistorius, P., Puskic, P.S., Reis, A.O. de A., Reisinger, R.R., Santos, M., Tarszisz, E., Tixier, P., Trathan, P.N., Wege, M., Wienecke, B., 2020. Marine ecosystem assessment for the Southern Ocean: birds and marine mammals in a changing climate. Front. Ecol. Evol. 8. https://doi.org/10.3389/fevo.2020.566936.

Blain, S., Tréguer, P., Belviso, S., Bucciarelli, E., Denis, M., Desabre, S., Fiala, M., Martin Jézéquel, V., Le Fèvre, J., Mayzaud, P., Marty, J.C., Razous, S., 2001. A biogeochemical study of the island mass effect in the context of the iron hypothesis: Kerguelen Islands, Southern Ocean. Deep. Res. Part I Oceanogr. Res. Pap. 48, 163–187. https://doi.org/10.1016/S0967-0637(00)00047-9.

Blain, S., Quéguiner, B., Armand, L., Belviso, S., Bommel, B., Bopp, L., Bowie, A., Brunet, C., Brussaard, C., Carlotti, F., Christaki, U., Corbière, A., Durand, I., Ebersbach, F., Fuda, J.L., Garcia, N., Gerringa, L., Griffiths, B., Guique, C., Guillerm, C., Jacquet, S., Jeandel, C., Laan, P., Lefèvre, D., Lo Monaco, C., Malits, A., Mosseri, J., Obernosterer, I., Park, Y.H., Picheral, M., Pondaven, P., Remenyi, T., Sandroni, V., Sarthou, G., Savoye, N., Scouvré, L., Souhaut, M., Thuiller, D., Timmermans, K., Trull, T., Uitz, J., Van Beek, P., Veldhuis, M., Vincent, D., Viollier, E., Vong, L., Wagener, T., 2007. Effect of natural iron fertilization on carbon sequestration in the Southern Ocean. Nature 446, 1070–1074. https://doi.org/10.1038/nature05700.

Blain, S., Sarthou, G., Laan, P., 2008. Distribution of dissolved iron during the natural iron-fertilization experiment KEOPS (Kerguelen Plateau, Southern Ocean). Deep. Res. Part I Oceanogr. Res. Pap. 55, 594–605. https://doi.org/10.1016/j.dsr2.2007.12.028.

Blain, S., Capparos, J., Guéneugues, A., Obernosterer, I., Oriol, L., 2015. Distributions and stoichiometry of dissolved nitrogen and phosphorus in the iron-fertilized region near Kerguelen (Southern Ocean). Biogeosciences 12, 623–635. https://doi.org/10.5194/bg-12-623-2015.

Bokhorst, S., Huiskes, A., Convey, P., Aerts, R., 2007. External nutrient inputs into terrestrial ecosystems of the Falkland Islands and the maritime Antarctic region. Polar Biol. 30, 1315–1321. https://doi.org/10.1007/s00300-007-0292-0.

Bokhorst, S., Convey, P., Aerts, R., 2019a. Nitrogen inputs by marine vertebrates drive abundance and richness in Antarctic terrestrial ecosystems. Curr. Biol. 29, 1721–1727.e3. https://doi.org/10.1016/j.cub.2019.04.038.

Bokhorst, S., van Logtestijn, R., Convey, P., Aerts, R., 2019b. Nitrogen isotope fractionation explains the 15N enrichment of Antarctic cryptogams by volatilized ammonia from penguin and seal colonies. Polar Res. 38, 1–9. https://doi.org/10.3326/polar.v38.3355.

Bonadonna, F., Lea, M.A., Guinet, C., 2000. Foraging routes of Antarctic fur seals (*Arctocephalus gazella*) investigated by the concurrent use of satellite tracking and time-depth recorders. Polar Biol. 23, 149–159. https://doi.org/10.1007/s003000050021.

Booth, C.G., Guilpin, M., Darias-O'Hara, A.-K., Ransijn, J.M., Ryder, M., Rosen, D., Piotta, E., Smout, S., McHuron, E.A., Nabe-Nielsen, J., Costa, D.P., 2023. Estimating energetic intake for marine mammal bioenergetic models. Conserv. Physiol. 11, 1–22. https://doi.org/10.1093/conphys/coac083.

Bost, C.A., Zorn, T., Le Maho, Y., Duhamel, G., 2002. Feeding of diving predators and diel vertical migration of prey: king penguins' diet versus trawl sampling at Kerguelen Islands. Mar. Ecol. Prog. Ser. 227, 51–61. https://doi.org/10.3354/meps227051.

Bowie, A.R., Van Der Merwe, P., Quéroué, F., Trull, T., Fourguez, M., Planchon, F., Sarthou, G., Chever, F., Townsend, A.T., Obernosterer, I., Sallée, J.B., Blain, S., 2015. Iron budgets for three distinct biogeochemical sites around the Kerguelen archipelago (Southern Ocean) during the natural fertilisation study, KEOPS-2. Biogeosciences 12, 4421–4445. https://doi.org/10.5194/bg-12-4421-2015.

Boyd, I.L., 1999. Foraging and provisioning in Antarctic fur seals: interannual variability in time-energy budgets. Behav. Ecol. 10, 198–208.

Boyd, I.L., 2002. Estimating food consumption of marine predators: Antarctic fur seals and macaroni penguins. J. Appl. Ecol. 39, 103–119. https://doi.org/10.1046/j.1365-2664.2002.00697.x.

Boyd, I.L., Lunn, N.J., Barton, T.R., 1991. Time Budgets and Foraging Characteristics of Lactating Antarctic Fur Seals. J. Anim. Ecol. 60, 577–592.

Boyd, P.W., Watson, A.J., Law, C.S., Abraham, E.R., Trull, T., Murdoch, R., Bakker, D.C. E., Bowie, A.R., Buesseler, K.O., Chang, H., Charette, M., Croot, P., Downing, K., Frew, R., Gall, M., Hadfield, M., Hall, J., Harvey, M., Jameson, G., Laroche, J., Liddicoat, M., Ling, R., Maldonado, M.T., Mckay, R.M., Nodder, S., Pickmere, S., Pridmore, R., Rintoul, S., Safi, K., Sutton, P., Strzepek, R., Tanneberger, K., Turner, S., Waite, A., Zeldis, J., 2000. A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization. Nature 407, 695–702.

Chapman, C.C., Lea, M.A., Meyer, A., Sallée, J.B., Hindell, M., 2020. Defining Southern Ocean fronts and their influence on biological and physical processes in a changing climate. Nat. Clim. Chang. 10, 209–219. https://doi.org/10.1038/s41558-020-0705-4.

Cherel, Y., Guinet, C., Tremblay, Y., 1997. Fish prey of Antarctic fur seals *Arctocephalus gazella* at Ile de Croy. Kerguelen. Polar Biol. 17, 87–90. https://doi.org/10.1007/s003000050109.

Chevallay, M., Guinet, C., Goulet-Tran, D., Jeanniard du Dot, T., 2024. Sealing the deal – Antarctic fur seals' active hunting tactics to capture small evasive prey revealed by miniature sonar tags. J. Exp. Biol. 227. https://doi.org/10.1242/jeb.246937.

Chouvelon, T., Gilbert, L., Caurant, F., Méndez-Fernandez, P., Bustamante, P., Brault-Favrou, M., Spitz, J., 2022a. Nutritional grouping of marine forage species reveals contrasted exposure of high trophic levels to essential micro-nutrients. Oikos 2022, e08844. https://doi.org/10.1111/oik.08844.

Chouvelon, T., Munschy, C., Bruzac, S., Caurant, F., Churlaud, C., Crochet, S., Guillou, G., Mauffret, A., Méndez-Fernandez, P., Niol, J., Sireau, T., Steinberg, C., Wessel, N., Spitz, J., 2022b. High inter-species variability in elemental composition of the twilight zone fauna varies implications for predators and exploitation by humans. Environ. Res. 204, 112379. https://doi.org/10.1016/j.envres.2021.112379.

Chowdhury, M.J., Blust, R., 2011. Strontium. In: Fish Physiology. Academic Press, pp. 351–390. https://doi.org/10.1016/S1546-5098(11)31029-1.

Coleman, D.C., Reid, C.P.P., Cole, C.V., 1983. Biological strategies of nutrient cycling in soil systems. Adv. Ecol. Res. 13, 1–55. https://doi.org/10.1016/S0065-2504(08)60107-5.

Costa, D.P., Croxall, J.P., Duck, C.D., Costa, D.P., Croxall, J.P., Duck, C.D., 1989. Foraging energetics of Antarctic Fur seals in relation to changes in prey availability. Ecology 70, 596–606.

van Der Merwe, P., Bowie, A.R., Quéroué, F., Armand, L., Blain, S., Chever, F., Davies, D., Dehairs, F., Planchon, F., Sarthou, G., Townsend, A.T., Trull, T.W., 2015. Sourcing the iron in the naturally fertilised bloom around the Kerguelen plateau: particulate trace metal dynamics. Biogeosciences 12, 739–755. https://doi.org/10.5194/bg-12-739-2015.

Doidge, D.W., Croxall, J.P., 1989. Factors affecting weaning weight in Antarctic fur seals *Arctocephalus gazella* at South Georgia. Polar Biol. 9, 155–160. https://doi.org/10.1007/BF00297170.

Doughty, C.E., Roman, J., Faurby, S., Wolf, A., Haque, A., Bakker, E.S., Malhi, Y., Dunning, J.B., Svenning, J.C., 2016. Global nutrient transport in a world of giants. Proc. Natl. Acad. Sci. USA 113, 868–873. https://doi.org/10.1073/pnas.1502549112.

D'Ovidio, F., Della Penna, A., Trull, T.W., Nencioli, F., Pujol, M.I., Rio, M.H., Park, Y.H., Cotté, C., Zhou, M., Blain, S., 2015. The biogeochemical structuring role of horizontal stirring: Lagrangian perspectives on iron delivery downstream of the Kerguelen Plateau. Biogeosciences 12, 5567–5581. https://doi.org/10.5194/bg-12-5567-2015.

Dubeux, J.C.B., Sollenberger, L.E., Mathews, B.W., Scholberg, J.M., Santos, H.Q., 2007. Nutrient cycling in warm-climate grasslands. Crop Sci. 47, 915–928. https://doi.org/10.2135/cropsci2006.09.0581.

Duhamel, G., Péron, C., Sinégre, R., Chazeau, C., Gasco, N., Hauteccœur, M., Martin, A., Durand, I., Cause, R., 2017. Important readjustments in the biomass and distribution of groundfish species in the northern part of the Kerguelen Plateau and Skiff Bank. Second Kerguelen Plateau Symp. Mar. Ecosyst. Fish. 135–184.

Erskine, P.D., Bergstrom, D.M., Schmidt, S., Stewart, G.R., Tweedie, C.E., Shaw, J.D., 1998. Subantarctic Macquarie Island - a model ecosystem for studying animal-derived nitrogen sources using 15N natural abundance. Oecologia 117, 187–193. https://doi.org/10.1007/s004420050647.

Filzmoser, P., Hron, K., 2009. Contribution analysis for compositional data. Math. Geosci. 41, 905–919. https://doi.org/10.1007/s11004-008-9196-y.

Filzmoser, P., Hron, K., Reimann, C., 2009. Principal component analysis for compositional data with outliers. Environmetrics 20, 621–632. https://doi.org/10.1002/env.

Filzmoser, P., Hron, K., Templ, M., 2018. Applied Compositional Data Analysis with Worked Examples in R. Springer Nature Switzerland.

Gilbert, L., Jeanniard-du-Dot, T., Authier, M., Chouvelon, T., Spitz, J., 2023a. Composition of cetecephalan communities worldwide shapes their contribution to ocean nutrient cycling. Nat. Commun. 14, 5823. https://doi.org/10.1038/s41467-023-41532-y.

Gilbert, L., Spitz, J., Jeanniard-du-Dot, T., 2023b. Pack-ice seals contribute to biological transfers of iron in the Southern Ocean. Polar Biol. https://doi.org/10.1007/s00300-023-03198-6.

Gilbert, L., Jeanniard-du-Dot, T., Chevallay, M., Spitz, J., 2025. Major and trace nutrient concentrations in sub-Antarctic forage fish around the Kerguelen Islands: All are not
equal for nutrient recycling by top predators. J. Exp. Mar. Biol. Ecol. https://doi.org/10.1016/j.jembe.2025.152097. XX(YY), ZZ-ZZ.

Goldsworthy, S.D., 1995. Differential expenditure of maternal resources in Antarctic fur seals, *Arctocephalus gazella*, at heard island, southern Indian Ocean. Behav. Ecol. 6, 218–228. https://doi.org/10.1093/beheq/6.2.218.

Goldsworthy, S.D., 1999. Maternal attendance behaviour of sympatrically breeding Antarctic and subantarctic fur seals, *Arctocephalus spp.*, at Macquarie Island. Polar Biol. 21, 316–325. https://doi.org/10.1007/s003000050368.

Goldsworthy, S.D., 2008. Antarctic fur seal: *Arctocephalus gazella*, Peters 1875. In: Van Dyck, S., Strahan, R. (Eds.), Mammals of Australia. Reed New Holland, Sydney, pp. 720–722. https://doi.org/10.1007/978-3-030-63177-2-4.

Grant, M.L., Bond, A.L., Reichman, S.M., Lavers, J.L., 2024. Seabird transported contaminants are dispersed in island ecosystems. Chemosphere 361, 142483. https://doi.org/10.1016/j.chemosphere.2024.142483.

Green, K., Williams, R., 1986. Observations on food remains in faeces of elephant, leopard and crabeye seals. Polar Biol. 6, 43–45. https://doi.org/10.1007/BF00446239.

Green, K., Burton, H.R., Williams, R., 1989. The diet of Antarctic fur seals *Arctocephalus gazella* during the breeding season at heard island. Antarct. Sci. 1, 317–324. https://doi.org/10.1007/BF02390431.

Guinet, C., Cherel, Y., Ridoux, V., Jouventin, P., 1996. Consumption of marine resources by seabirds and seals in Crozet and Kerguelen waters: changes in relation to consumer biomass 1962-85. Antarct. Sci. 8, 23–30. https://doi.org/10.1017/S095410296000053.

Guinet, C., Dubroca, L., Lea, M.A., Goldsworthy, S., Cherel, Y., Duhamel, G., Bonadonna, F., Donnay, J.P., 2001. Spatial distribution of foraging in female antarctic fur seals *Arctocephalus gazella* in relation to oceanographic variables: A scale-dependent approach using geographic information systems. Mar. Ecol. Prog. Ser. 219, 251–264. https://doi.org/10.3354/meps219251.

Hassler, C.S., Schoemann, V., Boye, M., Tagliabue, A., Rozmarynowycz, M., McKay, R.M. L., 2012. Iron bioavailability in the Southern Ocean. Oceanography and Marine Biology. CRC Press 10–73.

He, Z.L., Yang, X.E., Stoffella, P.J., 2005. Trace elements in agroecosystems and impacts on the environment. J. Trace Elem. Med. Biol. 19, 125–140. https://doi.org/10.1016/j.jtemb.2005.02.010.

Hindell, M.A., Lea, M.-A., Bost, C., Charrassin, J., Gales, N., Goldsworthy, S., Page, B., Robertson, G., Wienecke, B., Toole, M.O., Guinet, C., 2011. Foraging habits of top predators, and areas of ecological significance, on the Kerguelen Plateau. The Kerguelen Plateau: Marine Ecosystem and Fisheries. 203–215.

Hofmeyr, G.J.G., Bester, M.N., Jonker, F.C., 1997. Changes in population sizes and distribution of fur seals at Marion Island. Polar Biol. 17, 150–158. https://doi.org/10.1007/s003000050117.

Hu, X., Wei, X., Ling, J., Chen, J., 2021. Cobalt: an essential micronutrient for plant growth? Front. Plant Sci. 12, 1–24. https://doi.org/10.3389/fpls.2021.768523.

Hunt, B.P.V., Espinasse, B., Pakhomov, E.A., Cherel, Y., Cotté, C., Delegrange, A., Henschke, N., 2021. Pelagic food web structure in high nutrient low chlorophyll (HNLC) and naturally iron fertilized waters in the Kerguelen Islands region. *Antarctic Ocean. J. Mar. Syst.* 224. https://doi.org/10.1016/j.jmarsys.2021.103625.

Jeanniard-du-Dot, T., 2015. Foraging Strategies and Efficiencies of Lactating Northern and Antarctic Fur Seal: Implications for Reproductive Success. University of British Columbia, Canada.

Jeanniard-du-Dot, T., Guinet, C., 2021. Foraging capacities, behaviors and strategies of Otiarids and Odobenids. In: Ethology and Behavioral Ecology of Otiarids and the Odobenid. Springer Nature Switzerland, pp. 65–99. https://doi.org/10.1007/978-3-030-59184-7-4.

Jeanniard-du-Dot, T., Trites, A.W., Arnould, J.P.Y., Guinet, C., 2017a. Reproductive success is energetically linked to foraging efficiency in Antarctic fur seals. PLoS One 12, e0174001.

Jeanniard-du-Dot, T., Trites, A.W., Arnould, J.P.Y., Speakman, J.R., Guinet, C., 2017b. Activity-specific metabolic rates for diving, transiting, and resting at sea can be estimated from time-activity budgets in free-ranging marine mammals. Ecol. Evol. 7, 2969–2976. https://doi.org/10.1002/ece3.2546.

Jones, K.A., Ratcliffe, N., Votier, S.C., Lisovski, S., Bonner-Lebrun, A.-S., Staniland, I.J., 2021. Sexual segregation in juvenile Antarctic fur seals. Oecologia 197, 339–352.

Keiver, K.M., Ronald, K., Beamish, F.W.H., 1984. Metabolizable energy requirements for maintenance and faecal and urinary losses of juvenile harp seals (Phoca groenlandica). Can. J. Zool. 62, 769–776. https://doi.org/10.1139/z84-110.

Kimberley, A., Alan Blackburn, G., Duncan Whyatt, J., Smart, S.M., 2014. Traits of plant communities in fragmented forests: the relative influence of habitat spatial configuration and local abiotic conditions. J. Ecol. 102, 632–640. https://doi.org/10.1111/1365-2745.12222.

Kleiber, M., 1975. The fire of life. An introduction to animal energetics, the fire of life. An introduction to animal energetics. John Wiley & Sons, Inc., New York: London https://doi.org/10.1086/403606.

Koubbi, P., Mignard, C., Causse, R., Da Silva, O., Baudena, A., Bost, C., Cotté, C., D'Ovidio, F., Della Penna, A., Delord, K., Fabri-Ruiz, S., Ferrieux, M., Guinet, C., Lo Monaco, C., Saucéde, T., Weimerskirch, H., 2016. Ecoregionalisation of the Kerguelen and Crozet oceanic zone. CCAMLR Document WG-EMM, Part II. https://doi.org/10.13140/RG.2.2.17278.18246.

Kovalenko, K.E., Thomaz, S.M., Warfe, D.M., 2012. Habitat complexity: approaches and future directions. Hydrobiologia 685, 1–17. https://doi.org/10.1007/s10750-011-0974-z.

Kreft, H., Jetz, W., 2007. Global patterns and determinants of vascular plant diversity. Proc. Natl. Acad. Sci. USA 104, 5925–5930. https://doi.org/10.1073/pnas.0608361104.

Kumar, A., Prasad, M.N.V., 2018. Plant-lead interactions: transport, toxicity, tolerance, and detoxification mechanisms. Ecotoxicol. Environ. Saf. 166, 401–418. https://doi.org/10.1016/j.ecoenv.2018.09.113.

Lavelle, P., Dugdale, R., Scholes, R., Asefaw Berhe, A., Carpenter, E., Codispoti, L., Izac, A.-M., Lemoalle, R., Luizao, F., Scholes, M., Treguer, P., Ward, B., 2005. Nutrient cycling. In: Etchevers, J., Tiessen, H. (Eds.), Ecosystems and Human Well-Being: Current State and Trends: Findings of the Condition and Trends. Island Press, pp. 331–353.

Lavery, T.J., Roudnew, B., Gill, P., Seymour, J., Seuront, L., Johnson, G., Mitchell, J.G., Smetacek, V., 2010. Iron defecation by sperm whales stimulates carbon export in the Southern Ocean. Proc. R. Soc. B Biol. Sci. 277, 3527–3531. https://doi.org/10.1098/rspb.2010.0863.

Lavery, T.J., Roudnew, B., Seymour, J., Mitchell, J.G., Smetacek, V., Nicol, S., 2014. Whales sustain fisheries: blue whales stimulate primary production in the Southern Ocean. Mar. Mamm. Sci. 30, 888–904. https://doi.org/10.1111/mms.12108.

Lavery, T.J., Roudnew, B., Mitchell, J.G., 2015. Nitrogen transport from sea to land by a threatened and declining population of Australian sea lions (Neophoca cinerea) on Kangaroo Island, South Australia. Aust. Mammal. 37, 92–96. https://doi.org/10.1071/AM12029.

Lea, M.A., Dubroca, L., 2003. Fine-scale linkages between the diving behaviour of Antarctic fur seals and oceanographic features in the southern Indian Ocean.ICES J. Mar. Sci. 60, 990–1002. https://doi.org/10.1016/S1054-5500(02)00105-5.

Lea, M.A., Cherel, Y., Guinet, C., Nichols, P.D., 2002a. Antarctic fur seals foraging in the polar frontal zone: inter-annual shifts in diet as shown from fecal and fatty acid analyses. Mar. Ecol. Prog. Ser. 245, 281–297. https://doi.org/10.3354/meps245281.

Lea, M.A., Hindell, M., Guinet, C., Goldsworthy, S., 2002b. Variability in the diving activity of Antarctic fur seals, *Arctocephalus gazella* at Iles Kerguelen. Polar Biol. 25, 269–279. https://doi.org/10.1007/s00300-001-0339-6.

Lea, M.A., Guinet, C., Cherel, Y., Duhamel, G., Dubroca, L., Pruvost, P., Hindell, M., 2006. Impacts of climatic anomalies on provisioning strategies of a Southern Ocean predator. Mar. Ecol. Prog. Ser. 310, 77–94. https://doi.org/10.3354/meps310077.

Lea, M.A., Guinet, C., Cherel, Y., Hindell, M., Dubroca, L., Thalmann, S., 2008. Colony-based foraging segregation by Antarctic fur seals at the Kerguelen archipelago. Mar. Ecol. Prog. Ser. 358, 273–287. https://doi.org/10.3354/meps07305.

Lefèvre, D., Guigue, C., Obernosterer, I., 2008. The metabolic balance at two contrasting sites in the Southern Ocean: the iron-fertilized Kerguelen area and HNLC waters. Deep. Res. Part II Top. Stud. Oceanogr. 55, 766–776. https://doi.org/10.1016/j.dsr2.2007.12.006.

Lu, C., Tian, H., 2017. Global nitrogen and phosphorus fertilizer use for agriculture production in the past half century: shifted hot spots and nutrient imbalance. Earth Syst. Sci. Data 9, 181–192. https://doi.org/10.5194/essd-9-181-2017.

Luque, S.P., Arnould, J.P.Y., Miller, E.H., Cherel, Y., Guinet, C., 2007. Foraging behaviour of sympatric Antarctic and subantarctic fur seals: does their contrasting duration of lactation make a difference? Mar. Biol. 152, 213–224. https://doi.org/10.1007/s00227-007-0677-1.

March, D., Drago, M., Gazo, M., Parga, M., Rita, D., Cardona, L., 2021. Winter distribution of juvenile and sub-adult male Antarctic fur seals (*Arctocephalus gazella*) along the western Antarctic peninsula. Sci. Rep. 11, 1–14. https://doi.org/10.1038/s41598-021-01700-w.

Marzetz, V., Koussoroplis, A.M., Martin-Creuzburg, D., Striebel, M., Wacker, A., 2017. Linking primary producer diversity and food quality effects on herbivores: a biochemical perspective. Sci. Rep. 7, 11035. https://doi.org/10.1038/s41598-017-11183-3.

McInturf, A.G., Pollack, L., Yang, L.H., Spiegel, O., 2019. Vectors with autonomy: what distinguishes animal-mediated nutrient transport from abiotic vectors? Biol. Rev. 94, 1761–1773. https://doi.org/10.1111/brv.12525.

McIntyre, P.B., Jones, L.E., Flecker, A.S., Vanni, M.J., 2007. Fish extinctions alter nutrient recycling in tropical freshwaters. Proc. Natl. Acad. Sci. USA 104, 4461–4466. https://doi.org/10.1073/pnas.0608148104.

Mille, T., Cresson, P., Chouvelon, T., Bustamante, P., Brach-Papa, C., Sandrine, B., Rozuel, E., Bouchouche, M., 2018. Trace metal concentrations in the muscle of seven marine species: comparison between the Gulf of Lions (north-West Mediterranean Sea) and the Bay of Biscay (north-East Atlantic Ocean). Mar. Pollut. Bull. 135, 9–16. https://doi.org/10.1016/j.marpolbul.2018.05.051.

Monk, J.D., Schmitz, O.J., 2022. Landscapes shaped from the top down: predicting cascading predator effects on spatial biogeochemistry. Oikos 2022. https://doi.org/10.1111/oik.08554.

Moore, C.M., Hickman, A.E., Poulton, A.J., Seeyave, S., Lucas, M.I., 2007. Iron-light interactions during the CROZet natural iron bloom and EXport experiment (CROZEX): II-taxonomic responses and elemental stoichiometry. Deep. Res. Part II Top. Stud. Oceanogr. 54, 2066–2084. https://doi.org/10.1016/j.dsr2.2007.06.015.

Mooshammer, M., Wanek, W., Zechmeister-Boltenstern, S., Richter, A., 2014. Stoichiometric imbalances between terrestrial decomposer communities and their resources: mechanisms and implications of microbial adaptations to their resources. Front. Microbiol. 5, 1–10. https://doi.org/10.3389/fmicb.2014.00022.

Mouillot, D., Graham, N.A.J., Villéger, S., Mason, N.W.H., Bellwood, D.R., 2013. A functional approach reveals community responses to disturbances. Trends Ecol. Evol. 28, 167–177. https://doi.org/10.1016/j.tree.2012.10.004.

Nagajoyti, P.C., Lee, K.D., Sreekanth, T.V.M., 2010. Heavy metals, occurrence and toxicity for plants: a review. Environ. Chem. Lett. 8, 199–216. https://doi.org/10.1007/s10311-010-0297-8.

Nordoy, E.S., Sormo, W., Blix, A.S., 1993. In vitro digestibility of different prey species of minke whales (Balaenoptera acutorostrata). Br. J. Nutr. 70, 485–489. https://doi.org/10.1079/bjn19930142.
Page, B., Welling, A., Chambellant, M., Goldsworthy, S.D., Dorr, T., Van Veen, R., 2003. Population status and breeding season chronology of Heard Island fur seals. Polar Biol. 26, 219–224. https://doi.org/10.1007/s00300-003-0478-z.

Pichon, A., Morel, Y., Baraille, R., Quaresma, L.S., 2013. Internal tide interactions in the Bay of Biscay: observations and modelling. J. Mar. Syst. 109–110, S26–S44. https://doi.org/10.1016/j.jmarsys.2011.07.003.

van der Plas, F., 2019. Biodiversity and ecosystem functioning in naturally assembled communities. Biol. Rev. 94, 1220–1245. https://doi.org/10.1111/brv.12499.

Reid, K., Forcada, J., 2005. Causes of offspring mortality in the Antarctic fur seal, *Arctocephalus gazella*: the interaction of density dependence and ecosystem variability. Can. J. Zool. 83, 604–609. https://doi.org/10.1139/z05-045.

Reimchen, T.E., Mathewson, D.D., Hocking, M.D., Moran, J., Harris, D., 2003. Isotopic evidence for enrichment of salmon-derived nutrients in vegetation, soil, and insects in riparian zones in coastal British Columbia. Am. Fish. Soc. Symp. 59–70.

Roman, J., McCarthy, J.J., 2010. The whale pump: marine mammals enhance primary productivity in a coastal basin. PLoS One 5, e13255. https://doi.org/10.1371/journal.pone.0013255.

Roman, J., Nevins, J., Altabet, M., Koopman, H., McCarthy, J., 2016. Endangered right whales enhance primary productivity in the bay of fundy. PLoS One 11, 1–14. https://doi.org/10.1371/journal.pone.0156553.

Ronald, K., Keiver, K.M., Beamish, F.W.H., Frank, R., 1984. Energy requirements for maintenance and faecal and urinary losses of the grey seal (Halichoerus grypus). Can. J. Zool. 62, 1101–1105. https://doi.org/10.1139/z84-160.

Salminen, J., van Gestel, C.A.M., Oksanen, J., 2001. Pollution-induced community tolerance and functional redundancy in a decomposer food web in metal-stressed soil. Environ. Toxicol. Chem. 20, 2287–2295. https://doi.org/10.1002/etc.5620201022.

Santamans, A., Boluda, R., Picazo, A., Gil, C., Ramos-Miras, J., Tejedo, P., Pertierra, L.R., Benayas, J., Camacho, A., 2017. Soil features in rookeries of Antarctic penguins reveal sea to land biotransport of chemical pollutants. PLoS ONES 12 (8), 1–26. https://doi.org/10.1371/journal.pone.0181901.

Scherer-Lorenzen, M., Gessner, M.O., Beisner, B.E., Messier, C., Paquette, A., Petermann, J.S., Soininen, J., Nock, C.A., 2022. Pathways for cross-boundary effects of biodiversity on ecosystem functioning. Trends Ecol. Evol. 37, 454–467. https://doi.org/10.1016/j.tree.2021.12.009.

Shatova, O., Wing, S.R., Gault-Ringold, M., Wing, L., Hoffmann, L.J., 2016. Seabird guano enhances phytoplankton production in the Southern Ocean. J. Exp. Mar. Biol. Ecol. 483, 74–87. https://doi.org/10.1016/j.jembe.2016.07.004.

Shatova, O.A., Wing, S.R., Hoffmann, L.J., Wing, L.C., Gault-Ringold, M., 2017. Phytoplankton community structure is influenced by seabird guano enrichment in the Southern Ocean. Estuar. Coast. Shelf Sci. 191, 125–135. https://doi.org/10.1016/j.ecss.2017.04.021.

Shirihai, H., 2008. The Complete Guide to Antarctic Wildlife - Birds and Marine Mammals of the Antarctic Continent and the Southern Ocean, 2nd ed. Princeton University Press - Princeton and Oxford.

Sitters, J., Atkinson, C.L., Guelzow, N., Kelly, P., Sullivan, L.L., 2015. Spatial stoichiometry: cross-ecosystem material flows and their impact on recipient ecosystems and organisms. Oikos 124, 920–930. https://doi.org/10.1111/oik.02392.

Smith, L.V., McMinn, A., Martin, A., Nicol, S., Bowie, A.R., Lannuzel, D., Van der Merwe, P., 2013. Preliminary investigation into the stimulation of phytoplankton photophysiology and growth by whale faeces. J. Exp. Mar. Biol. Ecol. 446, 1–9. https://doi.org/10.1016/j.jembe.2013.04.010.

Smith, V.R., 2008. Energy flow and nutrient cycling in the Marion Island terrestrial ecosystem: 30 years on. Polar Rec. (Gr. Brit). 44, 211–226. https://doi.org/10.1017/S0032247407007218.

Spitz, J., Trites, A.W., Becquet, V., Brind'Amour, A., Cherel, Y., Galois, R., Ridoux, V., 2012. Cost of living dictates what whales, dolphins and porpoises eat: the importance of prey quality on predator foraging strategies. PLoS One 7. https://doi.org/10.1371/journal.pone.0050096.

Spitz, J., Ridoux, V., Trites, A.W., Laran, S., Authier, M., 2018. Prey consumption by cetaceans reveals the importance of energy-rich food webs in the Bay of Biscay. Prog. Oceanogr. 166, 148–158. https://doi.org/10.1016/j.poccean.2017.09.013.

Staniland, I.J., 2002. Investigating the biases in the use of hard prey remains to identify diet composition using Antarctic fur seals. Mar. Mamm. Sci. 18, 223–243.

Staniland, I.J., Robinson, S.L., 2008. Segregation between the sexes: Antarctic fur seals, *Arctocephalus gazella*, foraging at South Georgia. Anim. Behav. 75, 1581–1590. https://doi.org/10.1016/j.anbehav.2007.10.012.

Subalusky, A.L., Post, D.M., 2019. Context dependency of animal resource subsidies. Biol. Rev. 94, 517–538. https://doi.org/10.1111/brv.12465.

Tabeni, S., Larramendy, L., Szymański, C.R., Cona, M., 2022. The biodeposition process in native mammals: spatial distribution and influence of waste products on soil fertility in restored and grazed woodland. Restor. Ecol. 31, e13809. https://doi.org/10.1111/rec.13809.

Templ, M., Templ, B., 2021. Statistical analysis of chemical element compositions in food science: problems and possibilities. Molecules 26, 1–15. https://doi.org/10.3390/molecules26195752.

Templ, M., Hron, K., Filzmoser, P., Buccianti, A., 2011. robCompositions: an R-package for robust statistical analysis of compositional data. In: Pawlowsky-Glahn, V. (Ed.), Compositional Data Analysis: Theory and Applications. Wiley, pp. 341–355. https://doi.org/10.1002/9781119976462.

Thiebot, J.B., Cherel, Y., Trathan, P.N., Bost, C.A., 2012. Coexistence of oceanic predators on wintering areas explained by population-scale foraging segregation in space or time. Ecology 93, 122–130. https://doi.org/10.1890/11-0385.1.

Thiers, L., Delord, K., Bost, C.A., Guinet, C., Weimerskirch, H., 2017. Important marine sectors for the top predator community around Kerguelen Archipelago. Polar Biol. 40, 365–378. https://doi.org/10.1007/s00300-016-1964-4.

Thies, J., Grossman, J., 2006. The soil habitat and soil ecology. In: Biological Approaches to Sustainable Soil Systems. CRC Press, pp. 59–78. https://doi.org/10.1201/9781420017113.ch5.

Uchida, R., Silva, J.A., 2000. Essential nutrients for plant growth: nutrient functions and deficiency symptoms. Plant Nutr. Manag. Hawaii's soils, Approaches Trop. Subtrop. Agric, 31–55.

Wang, X., Morin, X., Zhang, J., Chen, G., Mao, L., Chen, Y., Song, Z., Du, Y., Ma, K., 2023. Geographical patterns and determinants in plant reproductive phenology duration. Front. Plant Sci. 14. https://doi.org/10.3389/fpls.2023.1199316.

Ward, J.H.J., 1963. Hierarchical grouping to optimize an objective function. J. Am. Stat. Assoc. 58, 236–244.

Wing, S.R., Jack, L., Shatova, O., Leichter, J.J., Barr, D., Frew, R.D., Gault-Ringold, M., 2014. Seabirds and marine mammals redistribute bioavailable iron in the Southern Ocean. Mar. Ecol. Prog. Ser. 510, 1–13. https://doi.org/10.3354/meps10923.

Wing, S.R., Wing, L.C., Shatova, O.A., Van Hale, R., 2017. Marine micronutrient vectors: seabirds, marine mammals and fishes egest high concentrations of bioactive metals in the subantarctic island ecosystem. Mar. Ecol. Prog. Ser. 563, 13–23. https://doi.org/10.3354/meps11978.

Wing, S.R., Wing, L.C., Barr, D., Genovese, S., Leichter, J.J., 2021. Penguins and seals transport limiting nutrients between offshore pelagic and coastal regions of Antarctica under changing sea ice. Ecosystems 24, 1203–1221. https://doi.org/10.1007/s10021-020-00578-5.

Wolf, A., Doughty, C.E., Malhi, Y., 2013. Lateral diffusion of nutrients by mammalian herbivores in terrestrial ecosystems. PLoS One 8, 1–10. https://doi.org/10.1371/journal.pone.0071352.