Krill availability in adjacent Adélie and gentoo penguin foraging regions near Palmer Station, Antarctica

Abstract

The Palmer Deep canyon along the West Antarctic Peninsula is a biological hotspot with abundant phytoplankton and krill supporting Adélie and gentoo penguin rookeries at the canyon head. Nearshore studies have focused on physical mechanisms driving primary production and penguin foraging, but less is known about finer-scale krill distribution and density. We designed two acoustic survey grids paired with conductivity-temperature-depth profiles within adjacent Adélie and gentoo penguin foraging regions near Palmer Station, Antarctica. The grids were sampled from January to March 2019 to assess variability in krill availability and associations with oceanographic properties. Krill density was similar in the two regions, but krill swarms were longer and larger in the gentoo foraging region, which was also less stratified and had lower chlorophyll concentrations. In the inshore zone near penguin colonies, depth-integrated krill density increased from summer to autumn (January-March) independent of chlorophyll concentration, suggesting a life history-driven adult krill migration rather than a resource-driven biomass increase. The daytime depth of krill biomass deepened through the summer and became decoupled from the chlorophyll maximum in March as diel vertical migration magnitude likely increased. Penguins near Palmer Station did not appear to be limited by krill availability during our study, and regional differences in krill depth match the foraging behaviors of the two penguin species. Understanding fine-scale physical forcing and ecological interactions in coastal Antarctic hotspots is critical for predicting how environmental change will impact these ecosystems.

A subsurface eddy associated with a submarine canyon increases availability and delivery of simulated Antarctic krill to penguin foraging regions

“…While preliminary data suggest there can be within-season variability in foraging grounds, we did not consider any within-summer variation here in producing our foraging regions. This foraging region was previously published in Nardelli et al (2021). The Adélie foraging region had an area of 221 km 2 , and 25% of this region overlapped with the eddy region.…”

“…Adélie and gentoo penguin foraging regions were identified using satellite tag data from PAL-LTER (Fig. 1; Nardelli et al 2021). Adélie penguins were tagged on Humble and Torgersen Islands, and gentoo penguins were tagged at Biscoe Island (Fig.…”

“…One area where this may occur is Palmer Deep Canyon (PDC), a submarine canyon along the WAP. This region is considered a biological hotspot due to high local phytoplankton concentrations (Kavanaugh et al 2015), high densities of krill (Bernard & Stein-berg 2013, Bernard et al 2017, Nardelli et al 2021, and many upper trophic level predators supported by the region in the austral summer (Fraser & Trivelpiece 1996). This includes central place foragers such as Adélie penguins Pygoscelis adeliae and gentoo penguins P. papua, whose chicks are dependent on local resources (Fraser & Trivelpiece 1996.…”

“…The high predator diversity and penguin foraging activity near PDC, and other Antarctic submarine canyons, suggests that prey resources are reliably abundant (Pickett et al 2018, Santora et al 2020, Nardelli et al 2021. However, the connection between PDC, prey distributions, and foraging activity is unclear.…”

Are the diets of sympatric Pygoscelid penguins more similar than previously thought?

“…Adélie and chinstrap penguins in the broader Antarctic Peninsula region typically exhibit a summer diet-based almost exclusively of krill (Lishman 1985). Such high amounts of krill in the diet of all three species suggest sufficient local availability of krill in the environment during the summer breeding period (Hinke et al 2007;Nardelli et al 2021). The apparent increase in the occurrence of krill in the diet of gentoo penguins since the early 1980s may imply a decline in availability of secondary prey items, particularly fish.…”