Examining the Connectivity of Antarctic Krill on the West Antarctic Peninsula: Implications for Pygoscelis Penguin Biogeography and Population Dynamics

doi:10.21203/rs.3.rs-2508180/v1

Download PDF

Article

Examining the Connectivity of Antarctic Krill on the West Antarctic Peninsula: Implications for Pygoscelis Penguin Biogeography and Population Dynamics

https://doi.org/10.21203/rs.3.rs-2508180/v1

This work is licensed under a CC BY 4.0 License

Journal Publication

published 26 Jul, 2023

Read the published version in Scientific Reports →

You are reading this latest preprint version

Antarctic krill (Euphausia superba) are considered a keystone species for higher trophic level predators along the West Antarctic Peninsula (WAP) during the austral summer. The connectivity of these populations may play a critical role in predator biogeography, especially for central-place foragers such as the Pygoscelis penguins that breed along the WAP during the austral summer. Here, we used a physical ocean model to examine adult krill connectivity in this region using simulated krill with realistic diel vertical migration behaviors across four austral summers. Specifically, we examined krill connectivity around the Adélie gap, a 400 km long region along the WAP with a distinct absence of Adélie penguin colonies, to determine if krill population connectivity around this feature played a role in its persistence. Our results indicate that krill populations north and south of the Adélie gap are nearly isolated from each other and that persistent current features play a role in this inter-region connectivity, or lack thereof. Our results indicate that simulated krill released within the Adélie gap are quickly advected from the region, suggesting that the lack of local krill recruit retention may play a role in the persistence of this biogeographic feature.

Earth and environmental sciences/Ecology/Biogeography

Earth and environmental sciences/Ecology/Population dynamics

Earth and environmental sciences/Ocean sciences/Physical oceanography

Pygoscelis penguins

Adélie gap

Antarctic krill

population connectivity

Regional Ocean Modeling System

Antarctic krill (Euphausia superba; henceforth referred to as krill) populations along the Western Antarctic Peninsula (WAP) are highly dynamic on both spatial and temporal scales^1–6, with cycles of abundance peaking approximately every 4–6-years^7,8. Recruitment of juvenile krill in the region has been linked to the extent of sea ice in the previous winter^9–12. Ice dynamics in the spring also play a role in phytoplankton distributions, size, and availability to krill recruits^13,14. These dynamics on the WAP have been linked to shifts in large scale climate oscillations like the Southern Annual Mode and El Nino Southern Oscillation^6,13,15. Furthermore, a growing krill fishery has added additional stressors to a delicate system^16,17.

Around the WAP, krill are thought to spawn off the continental shelf where eggs can sink into Circumpolar Deep Water and the heat associated with this water mass can assist in development^18–23. The resulting larvae migrate upwards and are advected downstream in the Antarctic Circumpolar Current (ACC) and eventually transported onto the continental shelf through trenches to their overwintering grounds under the coastal sea ice^{9,12, 24–26}. Both observations and modeling experiments suggest that krill spawning in the Bellingshausen Sea serves as a source of juvenile and adult krill along the central and southern regions of the peninsula, as well as to the South Shetland Islands and islands to the north of the WAP^27–31. Spawning in the Bellingshausen Sea does not, however, appear to serve as a source of krill to the northern tip of the WAP. Ocean currents around the tip of the WAP may isolate this region from the rest of the Peninsula, which relies instead on krill being fed from the Weddell Sea through the Coastal Current (CC; Fig. 1)^32–34.

During the austral summer, juvenile and non-spawning adult krill are found in coastal waters³⁰. While krill distributions along the WAP during this critical season are well studied^2,7,26,30, the connectivity among populations of adult krill during the austral summer is poorly understood. Because krill spawning and resulting recruitment is so spatially heterogeneous²², connectivity among regions can have an important influence on krill availability for central-place predators such as breeding Pygoscelis penguins that feed primarily on krill to help provision their growing chicks. Although all three Pygoscelis species breed along the WAP^35–38, there is a notable absence of Adélie penguin colonies along the Peninsula between the west coast of Trinity Peninsula and Anvers Island (orange box in Fig. 1). This region is known as the “Adélie gap” and stretches over 400 km along the coast of the WAP^38,39. It has been hypothesized that Adélie penguins north and south of the gap rely on different winter habitats in the Weddell and Bellingshausen Seas, respectively^39,40. However, Adélie penguins are known to range widely in the winter period, so such constraints on winter foraging do not necessarily preclude breeding within the Adélie gap⁴¹. As such, causal drivers for this biogeographic phenomenon remain poorly understood.

Here we examine how krill populations are connected along the WAP during the austral summer, with a special focus on connectivity across the Adélie gap. Using a physical ocean model, we simulate krill movement through the austral summer across the entire Antarctic Peninsula region from the Marguerite Trough to the Weddell Sea. We hypothesize that krill connectivity in this region of the WAP plays a significant role in Pygoscelis penguin population dynamics north and south of the Adélie gap. Adélie penguin populations are growing or stable north of the gap but are performing poorly elsewhere^42,43. Evidence supporting our hypotheses would suggest that krill population connectivity may help explain this dichotomy and, furthermore, is a factor that may influence the efficacy of regional krill fishing closures.

2.1 Regional Ocean Modeling System

To test how krill populations along the WAP are connected, we used an updated regional WAP implementation of the Regional Ocean Modeling System (ROMS)^44–46. Simulation parameters are provided in Supplementary Text A. This version of the model has a 1.5 km horizontal resolution and 24 vertical terrain-following layers. Dynamic sea ice and the interactions between floating ice shelves and the underlying waters are included^47,48. We simulated four austral summers from November to March: 2008–2009, 2009–2010, 2018–2019, and 2019–2020. We refer to each of these summers as a season, using the year in which the summer started to differentiate the simulations. Tidal forcing is from the CATS2008 regional Antarctic tidal model, with nodal corrections applied as necessary⁴⁹. Atmospheric forcing is from the Antarctic mesoscale Prediction System (AMPS)⁵⁰. Spatial resolution of AMPS varied between 15–20 km for the 2008 and 2009 seasons and increased to 8 km for the 2018 and 2019 seasons.

Simulated particles served as a proxy for krill (henceforth referred to as ‘simulated krill’) and were seeded on an approximately 8 km grid throughout the study region (Figure S1). A total of 5,574 simulated krill were released in the study regions (see Section 2.2; Fig. 1) during each release event. A total of 16 release events occurred, starting on 1 November and ending in mid-February of each simulation. Simulated krill were released every 7 days and were tracked for at least 30 days. To mimic the effect of vertical turbulence (which is parameterized in ROMS), simulated krill positions included a vertical random walk^51,52. Simulated krill were advected at every model time step (50 s) and positions were saved hourly.

To simulate krill behavior, diel vertical migration (DVM) was added to passive particles within ROMS. This behavior was added to ROMS particles previously to simulate both zooplankton⁵³ and krill⁵⁴. DVM in ROMS was based on local solar angle. When the sun was above the horizon, downward velocities were added to the advective and random vertical velocities in the model if the simulated krill was above a target depth. Inversely, when the sun was below the horizon, an upward velocity was added if the simulated krill was below a target depth (10 m).

Table 1

Previously published krill diel vertical migration (DVM) and *Pygoscelis* penguin foraging depth observations along the West Antarctic Peninsula (WAP) used to inform DVM simulations.
Daytime Depths (m)	Nighttime Depths (m)	Location	Season	Citation
37–48	NA	Palmer Deep	Summer	Bernard et al 2017⁵⁵
20–200	NA	Palmer Deep	Summer	Nardelli et al 2020⁵⁶
30	NA	Palmer Deep	Summer	Cimino et al 2016⁵⁷
100–140	20–30	South Georgia	Summer	Everson et al 1983⁵⁸
250	Near surface	Marguerite Bay & WAP continental shelf	Fall – Early Winter	Zhou and Dorland 2004⁵⁹
45–100	25–85	Northern WAP/South Shetland Islands	Summer	Godlewska and Klusek 1987⁶⁰
200–400	Upper 200	Wilhelmina Bay	Fall	Espinasse et al 2012⁶¹
40–80	20–40	Palmer Deep	Summer	Goodrich 2018⁶²
50–250	Upper 100	Branford Strait bays	Late spring	Kane et al 2018⁶³
10	50	Palmer Deep	Summer	Hudson et al., 2022⁵³

Simulated krill migration depths were based on previously published observations of krill DVM along the WAP (Table 1) and Pygoscelis penguin foraging depths (Table 2). Based on these observations, simulated krill DVM occurred between a minimum depth of 10 m and a maximum depth that varied between simulations (25, 50, 75, 100, or 150 m). Vertical migration speed was determined using observed krill swimming speeds in body lengths (BL) per second⁶³. The mean BL of krill in swarms in the northern WAP and observed in Pygoscelis penguin diets near Anvers Island is approximately 43 mm^64,65. With a mean vertical swimming speed of 0.335 BL s^− 1 in late spring⁶³, vertical migration speed of simulated krill was set to 0.014 m s^− 1. Reverse DVM (krill spending time near the surface during the day and migrating down at night) and non-migrating behaviors were not considered here.

Table 2

Previously published *Pygoscelis* penguin foraging depth observations along the West Antarctic Peninsula (WAP) used to inform diel vertical migration (DVM) simulations.
Species	Forage Depth (m)	Location	Season	Citation
Adélie	6–82	Palmer Deep	Summer	Pickett et al 2018⁶⁶
Gentoo	6–144	Palmer Deep	Summer	Pickett et al 2018⁶⁶
Chinstrap	25–45	South Orkney & King George Island	Summer	Lishman & Crozall 1983⁶⁷; Kokubun et al 2015⁶⁸

2.2 Regional Connectivity

Connectivity was examined between the following regions: south of Adelaide Island, south of the Adélie gap, the Adélie gap, the northern tip of the WAP, the South Shetland Islands, and Elephant Island (Fig. 1). These regions were based on the location of Pygoscelis penguin colonies from the Mapping Application for Penguin Populations and Projected Dynamics (MAPPPD)⁶⁹. Only areas approximately 40 km from these colonies were considered, as this approximates the maximum penguin summer foraging range for most colonies on the peninsula⁷⁰. To estimate penguin populations, population projections for the 2019 season from MAPPPD were used⁷¹. Two additional regions were considered as potential sources for krill: the north Weddell Sea and the coastal Bellingshausen Sea (Fig. 1). In these potential source regions, all areas where simulated krill were released are considered, regardless of distance to shore. Any simulated krill released in model water points under ice shelves were excluded.

We examined connectivity between the 8 regions using two different metrics: 1) the percentage of simulated krill released in one region that interacted with other regions⁷² and 2) the percent of time simulated krill spent in each region. For both metrics, we determined if simulated krill were present in a region using point.in.polygon in the R package ‘sp’⁷³. Metrics were averaged across release events that occurred within the chick-rearing period (December – March). Both metrics were averaged across simulated krill DVM behaviors to account for the variability in observed krill DVM behaviors.

Daily average currents from ROMS and simulated krill paths were examined as possible mechanisms of connectivity. Currents were interpolated to 10, 25, 50, 75, 100, and 150 m to match simulated DVM behaviors and averaged within the chick-rearing period across all seasons at each depth. To visualize simulated krill trajectories throughout the simulations, 20% of released particles with one of five DVM behaviors were randomly selected within each season to account for variability in these behaviors. Tracks were visualized across all seasons. For each persistent current feature, the number of penguin nests for each adjacent colony of the three Pygoscelis species were summed to determine the total number of birds impacted by these features. Colonies were considered adjacent to persistent current features if their 40 km foraging range overlapped with the feature.

3.1 Regional connectivity

Of the simulated krill released in the Weddell Sea, 40% entered the North WAP region, but they spent little (10%) time there (Fig. 2). Of the simulated krill released in the Weddell Sea, 8 and 7% entered the South Shetland and Elephant Island regions, respectively (Fig. 2a). Twelve percent of the simulated krill released in the Weddell Sea made it to the Adélie gap (Fig. 2). Apart from the North WAP region, simulated krill released in the Weddell Sea rarely spent much time (< 2%) in other regions (Fig. 2b).

The simulated krill released within the Adélie gap and the North WAP spent approximately half (40–54%) of their time within the regions in which they were released (Fig. 2). These simulated krill often entered the South Shetland and Elephant Islands regions, but rarely interacted with other regions apart from the Weddell Sea (Fig. 2). Nearly 40% of simulated krill released in the North WAP entered the Weddell Sea, but they did not spend much of their time there (5%, Fig. 2). Simulated krill released within the South Shetland and Elephant Islands regions spent the largest fractions of their time within their respective regions (18% and 37% respectively; Fig. 2b). These simulated krill rarely (< 5%) entered other regions outside the two island regions (Fig. 2a).

Simulated krill released in the South WAP dispersed more widely than simulated krill released from any other region (Fig. 2). However, simulated krill were relatively self-contained within the South WAP, spending 68% of their time there (Fig. 2b). No more than 16% of simulated krill released in the South WAP moved to any given region to the north while less than 10% moved into more southern regions (Fig. 2a). In addition, simulated krill that moved from the South WAP into other regions spent little time (< 5%) in those other regions (Fig. 2b).

Simulated krill released in the Bellingshausen Sea rarely passed through the other regions and spent little time (< 2%) there when they did (Fig. 2). Only 10% of simulated krill released in this region passed through the South WAP and adjacent Adelaide Island regions (Fig. 2a). Simulated krill originating in the Bellingshausen Sea rarely (< 1%) the Adélie gap, South Shetland Islands and Elephant Island regions (Fig. 2a). Simulated krill originating around Adelaide Island also rarely (< 1%) entered the South Shetland and Elephant Island regions, with most only passing through the South WAP and Bellingshausen Sea regions (Fig. 2a).

Due to the stochastic nature of the ocean dynamics, there were rare exceptions to these overall patterns. Simulated krill released in the Weddell Sea, for example, were advected into the South WAP region in the 2018 and 2019 seasons (Figures S2-3). Simulated krill released in the North WAP made it to the South WAP, albeit rarely in the 2008, 2018, and 2019 seasons (Figures S2-3). The reverse (simulated krill released in the South WAP traveling to the North WAP) was rare but observed in 3 seasons (2008, 2009, and 2019) (Figures S2-3). Simulated krill released around the Islands also only entered the Weddell Sea in the 2008 and 2009 seasons (Figures S2-3). Transport from the Island regions into the South WAP was observed in the 2018 season. In all these exceptions to the overall patterns described above, less than 1% of simulated krill entered these novel regions and these simulated krill spent less than 1% of their time in these regions (Figures S2-3).

3.2 Features driving connectivity

We identified 6 oceanic pathways in the model that promote or inhibit connectivity between regions of the WAP: the North WAP Loop Current (NWLC), Antarctic Circumpolar Current (ACC), Low Island Loop Current (LILC), Bransfield Current System (BCS), Bismarck and Gerlache Straits (BGS), and Cross Shelf Currents (CSC). Spaghetti plots (Fig. 3), animations (Supplemental Movies 1–8), and across season average currents (Figs. 4, S4-5) illustrated consistent features in the coastal ocean that drive patterns of connectivity among the regions examined here. These features are highlighted in Fig. 5.

North WAP Loop Current (NWLC)

The NWLC consisted of the CC moving out of the Weddell and around the tip of the Peninsula on the north and east (Figs. 4a, 5; Movies S1, 4). A southward current between the D’Urville and Joinville Islands and the tip of the peninsula completed the loop to the east of James Ross Island (Fig. 4, Movies S1, 4). This feature moved at ~ 20 cm s^− 1 (Figs. 4, S4-5). The NWLC helped retain simulated krill within the North WAP and Weddell Sea regions (Fig. 3a, d; Movies S1, 4).

Antarctic Circumpolar Current (ACC)

Some simulated krill from the regions south of the Adélie gap (Bellingshausen Sea, Adelaide Island, and South WAP) were advected along the continental shelf via the ACC (Fig. 3f-h, Movie S5-6, 8). This feature facilitated the transport of simulated krill from these southmost regions to the South Shetland and Elephant Island regions (Fig. 3f-h, Movie S5-8) and moved rapidly (> 20 cm s^− 1) along the continental shelf break (Fig. 4b). It also transported some simulated krill along the north shore of the South Shetland Islands from the LILC (see below; Fig. 3d-f, h).

Bransfield Current System (BCS)

The BCS consisted of 1) a northeasterly current along the south coast of the South Shetland Islands toward Elephant Island; 2) a southward current from Elephant Island towards the tip of the peninsula; 3) the CC moving out of the Weddell and to the southeast along the peninsula; and 4) a northward current between Tower and Astrolabe Islands (Figs. 4a, 5). These currents moved rapidly (~ 20 cm s^− 1) and were relatively consistent (Figs. 4a, S4). The BCS facilitated most of the transport from the South Shetland Islands to Elephant Island and helped retain simulated krill around the Adélie gap (Fig. 3b-c, e; Movie S3-5).

Bismarck & Gerlache Straits (BGS)

The BGS between Anvers Island and the Antarctic Continent served as the primary feature connecting the South WAP and Adélie gap regions (Figs. 3f, 5). Water moved rapidly through this tight channel (~ 20 cm s^− 1; Fig. 4b; Movie S6).

Cross Shelf Currents (CSC)

The CSC consisted of persistent currents moving from the continental shelf inshore (Figs. 3f, h; 4b; 5). These shoreward currents had relatively consistent speeds (~ 10 cm s^− 1) across the depths considered (Figs. 4b, 5). Unlike other features described here, the CSC refers to a set of three similar current systems along the continental shelf of the WAP. These currents facilitated the transport of simulated krill from the Bellingshausen Sea and Adelaide Island regions into the South WAP region, and likely helped retain simulated krill within the South WAP (Fig. 3f-h, Movies S6-8).

3.3 Penguins impacted by persistent features

To determine the impacts each of these features has on local Pygoscelis penguin populations, we calculated the total number of penguins adjacent to them from MAPPPD predictions (Table 3; Fig. 5). The ACC supported nearly 250,000 chinstraps across 73 colonies along the north shore of the South Shetland and Elephant Islands (Table 3). The CSC and BGS supported approximately 15,000 gentoo penguins combined across many small colonies (Table 3). While the CSC supported many small Adélie colonies, no Adélie colonies were present in the BGS (Table 3). Of the regions considered, BCS supported the largest number of chinstrap and gentoo penguins on the WAP (Table 3). North of the Adélie gap, the NWLC supported nearly a million Adélie penguins, the largest number of penguins across all features and species (Table 3). The LILC supported nearly 300,000 penguins with most of them being chinstraps (Table 3). The BGS supported the second largest number of gentoo penguins (Table 3). The total number of penguins supported by each feature increased moving south to north (Table 3).

Table 3

Number of nests (and number of colonies) adjacent to persistent current features on the West Antarctic Peninsula (WAP). Data are from Mapping Application for Penguin Populations and Projected Dynamics (MAPPPD) predictions.
Penguin species	Current Feature
Penguin species	Cross Shelf Currents (CSC)	Bismarck & Gerlache Straits (BGS)	Low Island Loop Current (LILC)	Bransfield Current System (BCS)	Antarctic Circumpolar Current (ACC)	North WAP Loop Current (NWLC)
Adélie	12,987 (35)	0 (0)	0 (0)	7,521 (8)	0 (0)	970,536 (24)
Chinstrap	3,727 (16)	11,208 (35)	273,214 (58)	421,762 (72)	248,777 (73)	20,568 (5)
Gentoo	22,344 (21)	33,198 (24)	20,286 (8)	43,477 (13)	3,347 (2)	10,810 (15)
Total	39,058 (72)	44,406 (59)	293,500 (66)	472,760 (93)	252,124 (75)	1,001,914 (44)

Pygoscelis penguins primarily consume krill during the austral summer^66,74,75. Krill distributions along the WAP are spatially and temporally heterogeneous^{1–6, 26} and, therefore, could play a role in penguin biogeography around the Adélie gap. This area is a 400 km long region along the coast of the WAP where no Adélie penguin colonies are present, despite foraging and migration behaviors that do not inhabit these penguins from inhabiting the region^40,41. Here, we used an ocean circulation model to determine how simulated krill are connected across coastal regions along the WAP. We specifically focused on how krill populations are connected north and south of the Adélie gap to determine if connectivity, or lack thereof, plays a role in penguin population dynamics in the region.

Simulated krill generally moved from south to north along the WAP. Simulated krill populations originating from points south of the Adélie gap generally remained within the region with a small fraction advected north to the South Shetland Islands via the ACC. For simulated krill originating just south of the Adélie gap in the South WAP, the BGS and LILC also moved simulated krill north to the South Shetland Islands. North of the gap, simulated krill were advected from the Weddell Sea to the Adélie gap via the CC. From here, simulated krill were advected north to the South Shetland Islands via the LILC. Occasionally, simulated krill returned to the Adélie gap via the BCS.

Here, we found that simulated krill south and north of the Adélie gap are, for the most part, isolated from each other. Connectivity between these regions is limited by a northward current around Low Island within the Adélie gap. This current, like many along the WAP, appears to be bathymetrically driven, following the contours of Boyd Strait between Low Island and the South Shetland Islands (Fig. 1)³². This current likely acts as a boundary between the Bransfield Strait and the rest of the peninsula, which have very different water column structures and water mass properties⁷⁶.

Rare exceptions to these patterns were observed across all four seasons simulated. These outlying events generally occurred in either the 2008–2009 seasons or 2018–2019 seasons. The coupling of these patterns in adjacent seasons suggests that changes in forcing dynamics may play a role. Possible forcing changes include wind, stratification, or eddying dynamics. Changes in the spatial resolution of atmospheric forcing may have also played a role. Further work is necessary to examine how changes in these forcing mechanisms may affect future connectivity north and south of the Adélie gap.

Despite these outlying events, overall patterns of connectivity between the regions studied here are remarkably consistent, with low variability, across four different austral summers. The current features highlighted here are persistent mechanisms for this connectivity and most are associated with bathymetric features. The CSC, for example, are driven by troughs and canyons crossing the continental shelf and the BCS follows bathymetric contours in the region. Persistent features were not found in areas on the continental shelf without strong bathymetry changes, illustrating the importance of bathymetry, and the resulting bathymetric steering of ocean currents in this region^77–79.

A majority of the persistent current features described here that drive krill connectivity along the WAP, including the ACC^32,80, CSC^77–79, BGS^32,81, BCS^{33,34, 81–83}, and LILC^80–82, have been observed along the WAP. Both the LILC and BCS have their components described in detail but are not often considered closed loop systems as we have described them here (Fig. 5). Entrainment of simulated krill by both these features is present, albeit not persistently in our observations. Therefore, more observations of these systems are necessary to determine if these features persist as closed loop systems or are simply connecting different current systems.

While the northward component of the NWLC associated with the CC has been observed previously (Fig. 1)^34,80,84, observations suggest that flow between the D’Urville and Joinville Islands and the tip of the WAP is northward, rather than southward as model simulations suggest^83,84. Animations of daily simulated krill locations illustrate that occasional northward transport of simulated krill is possible through this region despite mean southward flows (Fig. 4a, Movies S1, 4). Local water mass properties suggest that northward currents through this region is unlikely⁸⁵. Therefore, additional observations are necessary to determine if the southward component of the NWLC is present and persistent feature during the austral summer.

The addition of DVM to simulated krill, in addition to the persistence of current features across seasons, also likely helped drive the persistence of krill transport mechanisms. Ocean currents are highly variable in the surface due to the influences of wind on the surface mixed layer while the influence of wind is less prevalent in deeper waters which results in more consistent currents (see Movie S9-10 for examples within the Adélie gap). The addition of DVM to our simulated krill likely helped keep krill in these persistent current features and helped them avoid the variability associated with near-surface flows. The persistence of currents at depth may explain why simulated krill were well entrained within the BCS and LILC along the outside of the bathymetric features associated with each current system. This may be why these current features appeared as the closed loop systems observed and interactions with the mesoscale eddies associated with features like the BCS^32,34 were not as common.

It is critical to note that in modeling krill behavior, we made three assumptions that may impact our results. The first and foremost is that krill are only actively swimming in the vertical and are passive drifters in the horizontal. Krill form massive swarms and have been observed swimming in the horizontal on small scales^63,65. However, the directionality of this horizontal movement is unknown on the same horizontal scales of the model (1.5 km). While random walks have net zero displacement in the horizontal, previous krill movement modeling studies using monthly 1 km climatologies of surface currents have illustrated that random walks can impact krill distributions⁸⁶. Furthermore, individual based, small scale krill models have shown that horizontal movement can help krill move towards food (phytoplankton) and avoid predation^86–88. Therefore, future work should construct and incorporate a realistic krill horizontal movement model into simulations and determine its impact on krill transport and connectivity.

The second assumption made in this analysis is that krill regularly perform DVM to the depths simulated (25, 50, 75, 100, and 150 m). DVM is highly variable in krill throughout the WAP (Table 1). While we averaged krill accumulation metrics over our DVM behaviors to account for a portion of this variability, we did not simulate deeper DVM which has been shown to increase transport and/or retention by deep current features⁵³ to make sure that simulated krill were available to penguins within their vertical foraging ranges (Table 2). In addition, the krill have been shown to reduce or completely stop DVM over the austral summer in response to changing photoperiod^89,90. We also did not consider simulated krill without DVM behaviors, or reverse DVM. Reverse DVM, where simulated krill spend days in the surface feeding and migration downwards at night⁸⁹, may reduce the impact during the summer of the persistent current features identified as influencing population connectivity, since near-surface currents are heavily influenced by winds.

Our third assumption was that krill are homogeneously distributed throughout the WAP. As discussed previously, krill have high spatial and temporal variability along the WAP^{2–6, 26,30}. Therefore, it is important to interpret these results, not as absolute connectivity, but potential connectivity between the regions studied here. Future simulations should consider krill distribution and catch data from sources such as KRILLBASE to determine how the heterogenous distribution of krill along the WAP impacts these results. Areas previously defined as regions of high recruitment along the WAP²⁹ should also be considered. We hypothesize that the relative importance of the current features defined here will be directly correlated to krill spawning success in both the Weddell and Bellingshausen Seas.

One further limitation of our analysis is the modeling of the coastal buoyancy forces in ROMS. This iteration of the WAP circulation model is known to underestimate water column stratification, resulting in ocean currents with greater barotropic (depth-driven) and smaller baroclinic (density-driven) components than in situ observations suggest^44,76. This impacts the modeled CC around the tip of the WAP and along the coast, which is driven primarily by buoyancy due to coastal ice melt and coastal precipitation⁹¹. Improved modeling of the CC, especially down the coast of the WAP, may increase connectivity between regions north and south of the Adélie gap⁹¹.

Our results illustrate that adult krill populations in the Bellingshausen and Weddell Seas are only weakly connected to the rest of the Antarctic Peninsula waters. Penguin populations north of the Adélie gap have been doing well in recent years^42,43. The NWLC supports a number of Adélie penguins an order of magnitude greater than anywhere else in our study region (Table 3)⁴³. Colony sizes along the peninsula decrease as they become farther away from the Weddell Sea and the persistent features (NWLC and BCS) that transport krill out of this region. Therefore, the Weddell Sea may provide ample resources for the penguin colonies north of the gap via the NWLC, providing a compelling explanation for the aggregation of many large Adélie penguin colonies in this region.

Penguin populations south of the Adélie gap, however, do not receive krill from the Weddell, instead receiving krill from the Bellingshausen Sea and points south on the peninsula. Previous modeling studies show that the Bellingshausen Sea serves as a source of larval and juvenile krill²⁷. Pygoscelis penguin colonies, including the new gentoo colonies that have formed in this region in the 21st century³⁶, are generally smaller south of the Adélie gap than those to the north.

Penguins on both sides of the Adélie gap are adjacent to persistent current features that could potentially bring krill within their foraging ranges. Therefore, we hypothesize that the volume of resources available within each of these current features is likely highly heterogeneous and may be differentially impacted by changes to the environment observed over the last several decades. The Weddell Sea may serve as a krill sanctuary due to the extent and persistence of sea ice in the region, whereas sea ice – a critical overwintering habitat for krill^9–12 – is declining in the Bellingshausen^42,92,93. Significantly higher resource availability north of the Adélie gap from the Weddell Sea may be the cause of the significantly larger colonies there. Changing krill stocks and distributions as a result of climate change^1,2,94, albeit debated^95,96, have been linked to penguin population declines^16,97, changes in diet compositions in gentoos⁹⁸, and reproductive success of other krill predators such as the Antarctic fur seal (Arctocephalus gazella)⁹⁹ throughout the WAP, suggesting that krill availability may be declining to predators. However, recent modeling work and observations suggest that prey resources are not currently limiting for penguins south of the Adélie gap^66,100. Therefore, more studies are needed to determine if resource availability north and south of the Adélie gap is truly different and driving penguin population trends in these regions.

The larger penguin colonies north of the Adélie gap could persist due to transport of other prey species. Antarctic silverfish (Pleuragramma antarcticum) are considered another important prey species to Pygoscelis penguins^101–104. All life stages of the silverfish are strongly dependent on sea-ice extent¹⁰⁵. Therefore, the Weddell Sea may also serve as an important refuge for silverfish, in addition to overwintering krill. Previous modeling studies have illustrated that larval silverfish can be transported from the Weddell Sea to the North WAP and Adélie gap, likely through the NWLC and BE described here¹⁰⁶. In addition, the LILC may continue to act as a barrier to transport south of the Adélie gap¹⁰⁶. Increased availability of silverfish via the persistent current features described here, therefore, may be an additional driver of penguin population dynamics north of the Adélie gap. Silverfish are noticeably absent from penguin diets south of the WAP. However, the presence of smaller persistent current features may retain enough krill near penguin colonies to allow them to persist^54,101,107.

While our results illustrate that krill populations are not connected north and south of the Adélie gap and provide a plausible hypothesis for distinct penguin population dynamics on either side of this feature, they do not immediately discern why this biogeographic feature is present. Previous analysis of the US Antarctic Marine Living Resources long term monitoring program suggests that the Bransfield Strait between the South Shetland Islands and the coast of the WAP is a hotspot for krill recruitment²⁹. This suggests that prey resources should be plentiful enough to facilitate successful penguin foraging and colony establishment in the Adélie gap. Our results indicate that simulated krill released within the Adélie gap spent, on average, less than half of their time (40%) in the gap. If this region is a krill recruitment hotspot, recruits are presumably spawned in the Weddell Sea and subsequently transported into the Adélie gap region through the CC. Our results suggest that these krill recruits may be quickly advected out of the Adélie gap and into the South Shetland Islands and Elephant Island regions via the BCS. In addition, simulated krill released in other regions did not spend much time (< 17%) in the Adélie gap, if they entered this region at all. Therefore, we hypothesize that rapid currents in this region impede local recruit retention. Future work should test these hypotheses to determine if resource limitation via a lack of recruit retention is driving the Pygoscelis penguin population dynamics observed in the Adélie gap.

Not only do these results provide a testable hypothesis on driving mechanisms behind the Adélie gap but also are valuable for understanding the implications of krill fishery closures in different regions along the WAP. Our results suggest that closures north and south of the Adélie gap may only impact local krill stocks and have little influence elsewhere, with the exception of the South Shetland Islands. Therefore, proposed closures should take the connectivity of populations in account in order to have the desired effects on krill stocks.

Acknowledgements

The authors would like to thank Stony Brook Research Computing and Cyberinfrastructure, and the Institute for Advanced Computational Science at Stony Brook University for access to the innovative high-performance Ookami computing system, which was made possible by a $5M National Science Foundation grant (#1927880). Resources on Ookami were provided by allocation EES220028 from the Advanced Cyberinfrastructure Coordination Ecosystem: Services & Support (ACCESS) program, which is supported by National Science Foundation grants #2138259, #2138286, #2138307, #2137603, and #2138296. We also thank Eva Seigmann at Stony Brook University for her assistance in tuning ROMS for Ookami. K.G. is supported by the NSF Office of Polar Programs Postdoctoral Research Fellowship (Award #2138277).

Data Availability Statement

Bounding boxes for the regions used in this study, indexes used to subset simulated krill released within each region, and the code used to conduct connectivity calculations are available on GitHub (https://github.com/klgallagher/connectivity). Simulated krill trajectories (https://www.usap-dc.org/view/dataset/601655) and current velocity and direction data (https://www.usap-dc.org/view/dataset/601656) are archived at the United States Antarctic Program Data Center.

Author Contributions Statement

K.L.G. and H.J.L. conceived the presented idea. M.S.D. provided the version of ROMS used. K.L.G. ran model simulations and performed the analysis. All authors contributed to writing the manuscript.

Additional Information

Competing Interests Statement: The authors declare no competing interests.

Atkinson, A., Siegel, V., Pakhomov, E. & Rothery, P. Long-term decline in krill stock and increase in salps within the Southern Ocean. Nature 432, 100–103 (2004).
Atkinson, A. et al. Krill (Euphausia superba) distribution contracts southward during rapid regional warming. Nat. Clim. Change 9, 142–147 (2019).
Lascara, C. M., Hofmann, E. E., Ross, R. M. & Quetin, L. B. Seasonal variability in the distribution of Antarctic krill, Euphausia superba, west of the Antarctic Peninsula. Deep Sea Res. Part Oceanogr. Res. Pap. 46, 951–984 (1999).
Siegel, V., Loeb, V. & Gröger, J. Krill (Euphausia superba) density, proportional and absolute recruitment and biomass in the Elephant Island region (Antarctic Peninsula) during the period 1977 to 1997. Polar Biol. 19, 393–398 (1998).
Siegel, V., Reiss, C. S., Dietrich, K. S., Haraldsson, M. & Rohardt, G. Distribution and abundance of Antarctic krill (Euphausia superba) along the Antarctic Peninsula. Deep Sea Res. Part Oceanogr. Res. Pap. 77, 63–74 (2013).
Richerson, K., Santora, J. A. & Mangel, M. Climate variability and multi-scale assessment of the krill preyscape near the north Antarctic Peninsula. Polar Biol. 40, 697–711 (2017).
Steinberg, D. K. et al. Long-term (1993–2013) changes in macrozooplankton off the Western Antarctic Peninsula. Deep Sea Res. Part Oceanogr. Res. Pap. 101, 54–70 (2015).
Fraser, W. R. & Hofmann, E. E. A predator¹s perspective on causal links between climate change, physical forcing and ecosystem response. Mar. Ecol. Prog. Ser. 265, 1–15 (2003).
Daly, K. L. Overwintering growth and development of larval Euphausia superba: an interannual comparison under varying environmental conditions west of the Antarctic Peninsula. Deep Sea Res. Part II Top. Stud. Oceanogr. 51, 2139–2168 (2004).
Daly, K. L. Overwintering development, growth, and feeding of larval Euphausia superba in the Antarctic marginal ice zone. Limnol. Oceanogr. 35, 1564–1576 (1990).
Loeb, V. et al. Effects of sea-ice extent and krill or salp dominance on the Antarctic food web. Nature 387, 897–900 (1997).
Quetin, L. B. & Ross, R. M. Environmental Variability and Its Impact on the Reproductive Cycle of Antarctic Krill. Am. Zool. 41, 74–89 (2001).
Saba, G. K. et al. Winter and spring controls on the summer food web of the coastal West Antarctic Peninsula. Nat. Commun. 5, (2014).
Ducklow, H. W. et al. West Antarctic Peninsula: An Ice-Dependent Coastal Marine Ecosystem in Transition. Oceanography 26, 190–203 (2013).
Ducklow, H. W. et al. Marine pelagic ecosystems: the West Antarctic Peninsula. Philos. Trans. R. Soc. B Biol. Sci. 362, 67–94 (2007).
Trivelpiece, W. Z. et al. Variability in krill biomass links harvesting and climate warming to penguin population changes in Antarctica. Proc. Natl. Acad. Sci. 108, 7625–7628 (2011).
Watters, G. M., Hinke, J. T. & Reiss, C. S. Long-term observations from Antarctica demonstrate that mismatched scales of fisheries management and predator-prey interaction lead to erroneous conclusions about precaution. Sci. Rep. 10, 2314 (2020).
Klinck, J. M., Hofmann, E. E., Beardsley, R. C., Salihoglu, B. & Howard, S. Water-mass properties and circulation on the west Antarctic Peninsula Continental Shelf in Austral Fall and Winter 2001. Deep Sea Res. Part II Top. Stud. Oceanogr. 51, 1925–1946 (2004).
Marr, J. The natural history and geography of the Antarctic krill Euphausia superba Dana. Discov. Rep. 32, 37–465 (1962).
Quetin, L. B. & Ross, R. M. Depth distribution of developing Euphausia superba embryos, predicted from sinking rates. Mar. Biol. 79, 47–53 (1984).
Ross, R. M., Quetin, L. B. & Kirsch, E. Effect of temperature on developmental times and survival of early larval stages of Euphausia superba Dana. J. Exp. Mar. Biol. Ecol. 121, 55–71 (1988).
Hofmann, E. E. & Hüsrevoğlu, Y. S. A circumpolar modeling study of habitat control of Antarctic krill (Euphausia superba) reproductive success. Deep Sea Res. Part II Top. Stud. Oceanogr. 50, 3121–3142 (2003).
Siegel, V. Distribution and population dynamics of Euphausia superba: summary of recent findings. Polar Biol. 29, 1–22 (2005).
Hofmann, E. E., Klinck, J. M., Locarnini, R. A., Fach, B. & Murphy, E. Krill transport in the Scotia Sea and environs. Antarct. Sci. 10, 406–415 (1998).
Hofmann, E. E., Capella, J. E., Ross, R. M. & Quetin, L. B. Models of the early life history of Euphausia superba—Part I. Time and temperature dependence during the descent-ascent cycle. Deep Sea Res. Part Oceanogr. Res. Pap. 39, 1177–1200 (1992).
Atkinson, A. et al. Oceanic circumpolar habitats of Antarctic krill. Mar. Ecol. Prog. Ser. 362, 1–23 (2008).
Piñones, A., Hofmann, E. E., Daly, K. L., Dinniman, M. S. & Klinck, J. M. Modeling the remote and local connectivity of Antarctic krill populations along the western Antarctic Peninsula. Mar. Ecol. Prog. Ser. 481, 69–92 (2013).
Piñones, A., Hofmann, E. E., Daly, K. L., Dinniman, M. S. & Klinck, J. M. Modeling environmental controls on the transport and fate of early life stages of Antarctic krill (Euphausia superba) on the western Antarctic Peninsula continental shelf. Deep Sea Res. Part Oceanogr. Res. Pap. 82, 17–31 (2013).
Conroy, J. A., Reiss, C. S., Gleiber, M. R. & Steinberg, D. K. Linking Antarctic krill larval supply and recruitment along the Antarctic Peninsula. Integr. Comp. Biol. 60, 1386–1400 (2020).
Siegel, V. Krill (Euphausiacea) demography and variability in abundance and distribution. Can. J. Fish. Aquat. Sci. 57, 151–167 (2000).
Ross, R. M. et al. Palmer LTER: Patterns of distribution of five dominant zooplankton species in the epipelagic zone west of the Antarctic Peninsula, 1993–2004. Deep Sea Res. Part II Top. Stud. Oceanogr. 55, 2086–2105 (2008).
Moffat, C. & Meredith, M. Shelf–ocean exchange and hydrography west of the Antarctic Peninsula: a review. Philos. Trans. R. Soc. Math. Phys. Eng. Sci. 376, 20170164 (2018).
Sangrà, P. et al. The Bransfield Gravity Current. Deep Sea Res. Part Oceanogr. Res. Pap. 119, 1–15 (2017).
Thompson, A. F., Heywood, K. J., Thorpe, S. E., Renner, A. H. H. & Trasviña, A. Surface Circulation at the Tip of the Antarctic Peninsula from Drifters. J. Phys. Oceanogr. 39, 3–26 (2009).
Schrimpf, M. B., Che-Castaldo, C. & Lynch, H. J. Regional breeding bird assessment of the Antarctic Peninsula. Polar Biol. 43, 111–122 (2020).
Herman, R. et al. Update on the global abundance and distribution of breeding Gentoo Penguins (Pygoscelis papua). Polar Biol. 43, 1947–1956 (2020).
Strycker, N. et al. A global population assessment of the Chinstrap penguin (Pygoscelis antarctica). Sci. Rep. 10, 19474 (2020).
Poncet, S. & Poncet, J. Censures of Penguin populations of the Antarctic Peninsula, 1983-87. Bull.-Br. Antarct. Surv. 77, 109–129 (1987).
Fraser, WilliamR., Trivelpiece, WayneZ., Ainley, DavidG. & Trivelpiece, SusanG. Increases in Antarctic penguin populations: reduced competition with whales or a loss of sea ice due to environmental warming? Polar Biol. 11, (1992).
Fraser, W. R. & Trivelpiece, W. Z. Factors controlling the distribution of seabirds: Winter-summer heterogeneity in the distribution of adélie penguin populations. in Antarctic Research Series (eds. Hofmann, E. E., Ross, R. M. & Quetin, L. B.) vol. 70 257–272 (American Geophysical Union, 1996).
Hinke, J. T., Watters, G. M., Reiss, C. S., Santora, J. A. & Santos, M. M. Acute bottlenecks to the survival of juvenile Pygoscelis penguins occur immediately after fledging. Biol. Lett. 16, 20200645 (2020).
Wethington, M., Flynn, C., Borowicz, A. & Lynch, H. Adélie penguins north and east of the ‘Adélie gap’ continue to thrive in the face of dramatic declines elsewhere in the Antarctic Peninsula region. Sci. Rep. preprint, (2022).
Borowicz, A. et al. Multi-modal survey of Adélie penguin mega-colonies reveals the Danger Islands as a seabird hotspot. Sci. Rep. 8, 3926 (2018).
Hudson, K. et al. A Recirculating Eddy Promotes Subsurface Particle Retention in an Antarctic Biological Hotspot. J. Geophys. Res. Oceans 126, e2021JC017304 (2021).
Graham, J. A., Dinniman, M. S. & Klinck, J. M. Impact of model resolution for on-shelf heat transport along the West Antarctic Peninsula. J. Geophys. Res. Oceans 121, 7880–7897 (2016).
Haidvogel, D. B. et al. Ocean forecasting in terrain-following coordinates: Formulation and skill assessment of the Regional Ocean Modeling System. J. Comput. Phys. 227, 3595–3624 (2008).
Dinniman, M. S., Klinck, J. M. & Smith, W. O. A model study of Circumpolar Deep Water on the West Antarctic Peninsula and Ross Sea continental shelves. Deep Sea Res. Part II Top. Stud. Oceanogr. 58, 1508–1523 (2011).
Holland, D. M. & Jenkins, A. Modeling Thermodynamic Ice–Ocean Interactions at the Base of an Ice Shelf. J. Phys. Oceanogr. 29, 15 (1999).
Padman, L., Fricker, H. A., Coleman, R., Howard, S. & Erofeeva, L. A new tide model for the Antarctic ice shelves and seas. Ann. Glaciol. 34, 247–254 (2002).
Powers, J. G., Manning, K. W., Bromwich, D. H., Cassano, J. J. & Cayette, A. M. A DECADE OF ANTARCTIC SCIENCE SUPPORT THROUGH AMPS. Bull. Am. Meteorol. Soc. 93, 1699–1712 (2012).
Hunter, J. R., Craig, P. D. & Phillips, H. E. On the use of random walk models with spatially variable diffusivity. J. Comput. Phys. 106, 366–376 (1993).
Visser, A. Using random walk models to simulate the vertical distribution of particles in a turbulent water column. Mar. Ecol. Prog. Ser. 158, 275–281 (1997).
Hudson, K. et al. Subsurface Eddy Facilitates Retention of Simulated Diel Vertical Migrators in a Biological Hotspot. J. Geophys. Res. Oceans 127, (2022).
Hudson, K. et al. A subsurface eddy associated with a submarine canyon increases availability and delivery of simulated Antarctic krill to penguin foraging regions. Mar. Ecol. Prog. Ser. 702, 105–122 (2022).
Bernard, K. S. et al. Factors that affect the nearshore aggregations of Antarctic krill in a biological hotspot. Deep Sea Res. Part Oceanogr. Res. Pap. 126, 139–147 (2017).
Nardelli, S. C. et al. Krill availability in adjacent Adélie and gentoo penguin foraging regions near Palmer Station, Antarctica. Limnol. Oceanogr. 66, 2234–2250 (2021).
Cimino, M. A., Moline, M. A., Fraser, W., Patterson-Fraser, D. L. & Oliver, M. J. Climate-driven sympatry may not lead to foraging competition between congeneric top-predators. Sci. Rep. 6, (2016).
Everson I. Variations in vertical distribution and density of krill swarms in the vicinity of South Georgia. 27, 84–92 (1983).
Zhou, M. & Dorland, R. D. Aggregation and vertical migration behavior of Euphausia superba. Deep Sea Res. Part II Top. Stud. Oceanogr. 51, 2119–2137 (2004).
Godlewska, M. & Klusek, Z. Vertical distribution and diurnal migrations of krill ? Euphausia superba Dana ? from hydroacoustical observations, SIBEX, December 1983/January 1984. Polar Biol. 8, 17–22 (1987).
Espinasse, B. et al. Austral fall−winter transition of mesozooplankton assemblages and krill aggregations in an embayment west of the Antarctic Peninsula. Mar. Ecol. Prog. Ser. 452, 63–80 (2012).
Goodrich, C. SUSTAINED GLIDER OBSERVATIONS OF ACOUSTIC SCATTERING SUGGEST ZOOPLANKTON PATCHES ARE DRIVEN BY VERTICAL MIGRATION AND SURFACE ADVECTIVE FEATURES IN PALMER CANYON, ANTARCTICA. (University of Delaware, 2018).
Kane, M. K., Yopak, R., Roman, C. & Menden-Deuer, S. Krill motion in the Southern Ocean: quantifying in situ krill movement behaviors and distributions during the late austral autumn and spring: Krill motion in the Southern Ocean. Limnol. Oceanogr. 63, 2839–2857 (2018).
Fraser, W. Adelie penguin diet composition, preliminary analyses of whole lavaged samples, 1991 - present. (2020) doi:10.6073/PASTA/CF606695BFE2BEA52DAF431F9FF83272.
Tarling, G. A. et al. Variability and predictability of Antarctic krill swarm structure. Deep Sea Res. Part Oceanogr. Res. Pap. 56, 1994–2012 (2009).
Pickett, E. P. et al. Spatial niche partitioning may promote coexistence of Pygoscelis penguins as climate-induced sympatry occurs. Ecol. Evol. 8, 9764–9778 (2018).
Lishman, G. S. & Croxall, J. P. Diving Depths of the Chinstrap Penguin Pygoscelis Antarctica. Br. Antarct. Surv. Bullitin 61, 21–25 (1983).
Kokubun, N., Takahashi, A., Mori, Y., Watanabe, S. & Shin, H.-C. Comparison of diving behavior and foraging habitat use between chinstrap and gentoo penguins breeding in the South Shetland Islands, Antarctica. Mar. Biol. 157, 811–825 (2010).
Humphries, G. R. W. et al. Mapping Application for Penguin Populations and Projected Dynamics (MAPPPD): data and tools for dynamic management and decision support. Polar Rec. 53, 160–166 (2017).
Santora, J. A., LaRue, M. A. & Ainley, D. G. Geographic structuring of Antarctic penguin populations. Glob. Ecol. Biogeogr. 29, 1716–1728 (2020).
Che-Castaldo, C. et al. Pan-Antarctic analysis aggregating spatial estimates of Adélie penguin abundance reveals robust dynamics despite stochastic noise. Nat. Commun. 8, 832 (2017).
Kohut, J. T. et al. Variability in summer surface residence time within a West Antarctic Peninsula biological hotspot. Philos. Trans. R. Soc. Math. Phys. Eng. Sci. 376, 20170165 (2018).
Bivand, R. S., Pebesma, E. & Gomez-Rubio, V. Applied spatial data analysis with R. (Springer, 2013).
Wawrzynek-Borejko, J., Panasiuk, A., Hinke, J. T. & Korczak-Abshire, M. Are the diets of sympatric Pygoscelid penguins more similar than previously thought? Polar Biol. 45, 1559–1569 (2022).
Cimino, M. A., Fraser, W., Patterson-Fraser, D., Saba, V. S. & Oliver, M. J. Large-scale climate and local weather drive interannual variability in Adélie penguin chick fledging mass. Mar. Ecol. Prog. Ser. 513, 253–268 (2014).
Wang, X. et al. Variability and Dynamics of Along‐Shore Exchange on the West Antarctic Peninsula (WAP) Continental Shelf. J. Geophys. Res. Oceans (2022) doi:10.1029/2021JC017645.
Moffat, C., Owens, B. & Beardsley, R. C. On the characteristics of Circumpolar Deep Water intrusions to the west Antarctic Peninsula Continental Shelf. J. Geophys. Res. 114, (2009).
Martinson, D. G. & McKee, D. C. Transport of warm Upper Circumpolar Deep Water onto the western Antarctic Peninsula continental shelf. Ocean Sci. 8, 433–442 (2012).
Couto, N., Martinson, D. G., Kohut, J. & Schofield, O. Distribution of Upper Circumpolar Deep Water on the warming continental shelf of the West Antarctic Peninsula: UCDW ON THE WARMING WAP SHELF. J. Geophys. Res. Oceans 122, 5306–5315 (2017).
Hofmann, E. E., Klinck, J. M., Lascara, C. M. & Smith, D. A. Water Mass Distribution and Circulation West of the Antarctic Peninsula And Including Bransfield Strait. in Foundations for Ecological Research West of the Antarctic Peninsula 61–80 (American Geophysical Union (AGU), 1996). doi:10.1029/AR070p0061.
Zhou, M., Niiler, P. P. & Hu, J.-H. Surface currents in the Bransfield and Gerlache Straits, Antarctica. Deep Sea Res. Part Oceanogr. Res. Pap. 49, 267–280 (2002).
Savidge, D. K. & Amft, J. A. Circulation on the West Antarctic Peninsula derived from 6 years of shipboard ADCP transects. Deep Sea Res. Part Oceanogr. Res. Pap. 56, 1633–1655 (2009).
Sangrà, P. et al. The Bransfield current system. Deep Sea Res. Part Oceanogr. Res. Pap. 58, 390–402 (2011).
Collares, L. L., Mata, M. M., Kerr, R., Arigony-Neto, J. & Barbat, M. M. Iceberg drift and ocean circulation in the northwestern Weddell Sea, Antarctica. Deep Sea Res. Part II Top. Stud. Oceanogr. 149, 10–24 (2018).
Huneke, W. G. C., Huhn, O. & Schröeder, M. Water masses in the Bransfield Strait and adjacent seas, austral summer 2013. Polar Biol. 39, 789–798 (2016).
Richerson, K., Watters, G., Santora, J., Schroeder, I. & Mangel, M. More than passive drifters: a stochastic dynamic model for the movement of Antarctic krill. Mar. Ecol. Prog. Ser. 529, 35–48 (2015).
Cresswell, K. A. et al. Diel vertical migration of Antarctic krill (Euphausia superba) is flexible during advection across the Scotia Sea. J. Plankton Res. 31, 1265–1281 (2009).
Cresswell, K., Tarling, G. & Burrows, M. Behaviour affects local-scale distributions of Antarctic krill around South Georgia. Mar. Ecol. Prog. Ser. 343, 193–206 (2007).
Tarling, G. A. et al. Varying depth and swarm dimensions of open-ocean Antarctic krill Euphausia superba Dana, 1850 (Euphausiacea) over diel cycles. J. Crustac. Biol. (2018) doi:10.1093/jcbiol/ruy040.
Tarling, G. A. & Thorpe, S. E. Oceanic swarms of Antarctic krill perform satiation sinking. Proc. R. Soc. B Biol. Sci. 284, 20172015 (2017).
Moffat, C., Beardsley, R. C., Owens, B. & van Lipzig, N. A first description of the Antarctic Peninsula Coastal Current. Deep Sea Res. Part II Top. Stud. Oceanogr. 55, 277–293 (2008).
Veytia, D. et al. Circumpolar projections of Antarctic krill growth potential. Nat. Clim. Change 10, 568–575 (2020).
Stammerjohn, S. E., Martinson, D. G., Smith, R. C. & Iannuzzi, R. A. Sea ice in the western Antarctic Peninsula region: Spatio-temporal variability from ecological and climate change perspectives. Deep Sea Res. Part II Top. Stud. Oceanogr. 55, 2041–2058 (2008).
Atkinson, A. et al. Stepping stones towards Antarctica: Switch to southern spawning grounds explains an abrupt range shift in krill. Glob. Change Biol. gcb.16009 (2021) doi:10.1111/gcb.16009.
Krafft, B. A. et al. Standing stock of Antarctic krill (Euphausia superba Dana, 1850) (Euphausiacea) in the Southwest Atlantic sector of the Southern Ocean, 2018–19. J. Crustac. Biol. 41, ruab046 (2021).
Meyer, B. et al. Successful ecosystem-based management of Antarctic krill should address uncertainties in krill recruitment, behaviour and ecological adaptation. Commun. Earth Environ. 1, 1–12 (2020).
Forcada, J., Trathan, P. N., Reid, K., Murphy, E. J. & Croxall, J. P. Contrasting population changes in sympatric penguin species in association with climate warming. Glob. Change Biol. 12, 411–423 (2006).
McMahon, K. W. et al. Divergent trophic responses of sympatric penguin species to historic anthropogenic exploitation and recent climate change. Proc. Natl. Acad. Sci. 116, 25721–25727 (2019).
Forcada, J. & Hoffman, J. I. Climate change selects for heterozygosity in a declining fur seal population. Nature 511, 462–465 (2014).
Sailley, S. et al. Carbon fluxes and pelagic ecosystem dynamics near two western Antarctic Peninsula Adélie penguin colonies: an inverse model approach. Mar. Ecol. Prog. Ser. 492, 253–272 (2013).
Chapman, E., Hofmann, E., Patterson, D., Ribic, C. & Fraser, W. Marine and terrestrial factors affecting Adéliepenguin Pygoscelis adeliae chick growth and recruitment off the western Antarctic Peninsula. Mar. Ecol. Prog. Ser. 436, 273–289 (2011).
Ainley, D. G. et al. Post-fledging survival of Adélie penguins at multiple colonies: chicks raised on fish do well. Mar. Ecol. Prog. Ser. 601, 239–251 (2018).
Polito, M. J. et al. Integrating Stomach Content and Stable Isotope Analyses to Quantify the Diets of Pygoscelid Penguins. PLOS ONE 6, e26642 (2011).
Polito, M. et al. Contrasting specialist and generalist patterns facilitate foraging niche partitioning in sympatric populations of Pygoscelis penguins. Mar. Ecol. Prog. Ser. 519, 221–237 (2015).
La Mesa, M. & Eastman, J. T. Antarctic silverfish: life strategies of a key species in the high-Antarctic ecosystem. Fish Fish. 13, 241–266 (2012).
La Mesa, M., Piñones, A., Catalano, B. & Ashford, J. Predicting early life connectivity of Antarctic silverfish, an important forage species along the Antarctic Peninsula. Fish. Oceanogr. 24, 150–161 (2015).
Chapman, E. W., Hofmann, E. E., Patterson, D. L. & Fraser, W. R. The effects of variability in Antarctic krill (Euphausia superba) spawning behavior and sex/maturity stage distribution on Adélie penguin (Pygoscelis adeliae) chick growth: A modeling study. Deep Sea Res. Part II Top. Stud. Oceanogr.57, 543–558 (2010).

No competing interests reported.

Download PDF

Journal Publication

published 26 Jul, 2023

Read the published version in Scientific Reports →

Editorial decision: Major revision
27 Mar, 2023
Reviews received at journal
20 Mar, 2023
Reviewers agreed at journal
09 Mar, 2023
Reviews received at journal
08 Mar, 2023
Reviewers agreed at journal
03 Mar, 2023
Reviewers invited by journal
14 Feb, 2023
Editor assigned by journal
14 Feb, 2023
Editor invited by journal
26 Jan, 2023
Submission checks completed at journal
26 Jan, 2023
First submitted to journal
23 Jan, 2023

You are reading this latest preprint version

Examining the Connectivity of Antarctic Krill on the West Antarctic Peninsula: Implications for Pygoscelis Penguin Biogeography and Population Dynamics

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

2. Methods

2.1 Regional Ocean Modeling System

2.2 Regional Connectivity

3. Results

3.1 Regional connectivity

3.2 Features driving connectivity

3.3 Penguins impacted by persistent features

4. Discussion

Declarations

References

Additional Declarations

Supplementary Files

Status:

Journal Publication

Version 1