No 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.

Antarctic krill (Euphausia superba) larval production and overwinter survival drive recruitment variability, which in turn determines abundance trends. The Antarctic Peninsula has been described as a recruitment hot spot and as a potentially important source region for larval and juvenile krill dispersal. However, there has been no analysis to spatially resolve regional-scale krill population dynamics across life stages. We assessed spatiotemporal patterns in krill demography using two decades of austral summer data collected along the North and West Antarctic Peninsula since 1993. We identified persistent spatial segregation in the summer distribution of euphausiid larvae (E. superba plus other species), which were concentrated in oceanic waters along the continental slope, and E. superba recruits, which were concentrated in shelf and coastal waters. Mature female E. superba were more abundant over the continental shelf than the slope or coast. Euphausiid larval abundance was relatively localized and weakly correlated between the North and West Antarctic Peninsula, while E. superba recruitment was generally synchronized throughout the entire region. Euphausiid larval abundance along the West Antarctic Peninsula slope explained E. superba recruitment in shelf and coastal waters the next year. Given the localized nature of krill productivity, it is critical to evaluate the connectivity between upstream and downstream areas of the Antarctic Peninsula and beyond. Krill fishery catch distributions and population projections in the context of a changing climate should account for ontogenetic habitat partitioning, regional population connectivity, and highly variable recruitment.

The krill surplus hypothesis of unlimited prey resources available for Antarctic predators due to commercial whaling in the 20th century has remained largely untested since the 1970s. Rapid warming of the Western Antarctic Peninsula (WAP) over the past 50 years has resulted in decreased seasonal ice cover and a reduction of krill. The latter is being exacerbated by a commercial krill fishery in the region. Despite this, humpback whale populations have increased but may be at a threshold for growth based on these human-induced changes. Understanding how climate-mediated variation in prey availability influences humpback whale population dynamics is critical for focused management and conservation actions. Using an 8-year dataset (2013-2020), we show that inter-annual humpback whale pregnancy rates, as determined fromThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

No abstract