Abstract
AbstractThe 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.
Highlights
Growth (Kavanaugh et al 2015; Carvalho et al 2019), and to aggregate Antarctic krill (Euphausia superba), supporting large higher trophic level populations (Santora and Reiss 2011)
Previous studies show that austral summer krill distributions in the Palmer Deep canyon are influenced by physics and phytoplankton concentration based on foraging dives from satellite tag data from 2009 to 2019
The surveys created for this study are the start of a new data set introduced to the Palmer Antarctica Long-Term Ecological Research (LTER) project, designed to provide data on nearshore krill distributions at spatial and temporal scales that are relevant to penguin foraging ecology
Summary
Growth (Kavanaugh et al 2015; Carvalho et al 2019), and to aggregate Antarctic krill (Euphausia superba), supporting large higher trophic level populations (Santora and Reiss 2011). From 1976 to 2016 there was a krill abundance decline in the southwest Atlantic sector, and a southward range contraction that concentrated krill distribution along the West Antarctic Peninsula shelf (Atkinson et al 2019) This is notable because further warming could cause additional range contractions and decreased krill biomass near Palmer Station (Klein et al 2018), which in turn could increase penguin foraging efforts and decrease breeding success (Fraser and Hofmann 2003; Chapman et al 2011). Our results emphasize the importance of organismal life histories in understanding ecological interactions over seasonal scales, which is crucial for predicting how continued environmental change will impact krill and penguin populations in ecologically important coastal areas
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