How will Antarctic krill habitat respond to future climate change?

Antarctic krill are a key species of important Southern Ocean (SO) food webs. Krill have evolved to maximize success in the highly seasonal environment of the SO, which alternates between productive open ocean and sea ice-dominated habitats. This high degree of adaptation to their environment makes them potentially vulnerable to future climate changes.

When krill occupy open ocean habitats, habitat quality is maximized in cooler, productive waters. Thus, habitat is primarily defined by an environmental envelope of temperature and primary production. Using this relationship, we are the first to apply Earth System Model (ESM) primary production output to develop circumpolar projections for Antarctic krill habitat in the Southern Ocean. The results indicate that overall, krill growth habitat will be reasonably robust to projected changes (91% of habitat area will experience a relative change in Gross Growth Potential ± 20% by 2100). However, we also see a spatial shift in krill habitat in response to ocean warming, as well as a seasonal shift in habitat quality. This has implications for the access of sub-Antarctic predators to their primary prey source, as well as the potential reproductive output and abundance of Antarctic krill.

However, this analysis does not consider the important role of sea ice in the krill life cycle. Functioning as an overwinter nursery for larval krill, sea ice is thought to exert a strong control over their recruitment the following spring. Until now, under-ice habitat features that have been identified as important to larval recruitment, such as thickness and rugosity, had yet to be quantified. We present results from linking these overwintering sea-ice habitat qualities with krill recruitment. By using a sea-ice model forced with observations, we define relationships between sea ice features and krill condition and recruitment. This has informed our understanding of krill overwintering habitat and represents an important step in developing a trait-based model of the complete krill life cycle. This would enable future abundance and recruitment projections, allowing for more confident assessments of the impacts of climate change on SO food webs.