Flexibility in Antarctic krill Euphausia superba decouples diet and recruitment from overwinter sea-ice conditions in the northern Antarctic Peninsula

Abstract

Winter sea-ice conditions are considered important for Antarctic krill Euphausia superba survival and recruitment, yet few broad-scale longitudinal studies have examined the underlying relationships between winter conditions and krill recruitment. We used data from a 4 yr winter study of krill condition (lipid content), diet (stable isotopes and fatty acids), and length distributions around the northern Antarctic Peninsula to examine relationships among environmental variables (annual sea-ice cover, water column chlorophyll a [chl a], and upper mixed-layer water temperature), the condition and diet of krill, and recruitment success the following year. Diet indicators (lipid content, δ15N, δ13C, and the fatty acid ratios 16:1n-7/18:4n-3 and 18:1n-9/18:1n-7) in post-larvae were consistent among years regardless of sea-ice cover, suggesting that post-larval krill do not rely on sea-ice resources for overwinter survival. Diet indicators in larvae were more variable and suggest that larvae may feed on sea-ice resources when they are available but can still persist in the water column when they are not. Principal component analysis between environmental variables and diet indicators showed that water-column chl a was the only variable that significantly affected diet, regardless of annual changes in sea-ice cover. Extensive winter ice in one year did not translate into successful recruitment the following year. Krill demonstrate a high degree of flexibility with respect to overwinter habitat and diet, and the degree to which sea ice is important during different times of year and at different life stages may be more complex than previously thought.

Resource Colimitation Drives Competition Between Phytoplankton and Bacteria in the Southern Ocean

“…To maintain seawater dissolved Fe levels of >0.7 nM throughout winter in the SAZ, either Fe must be continuously supplied via deep winter mixing (Tagliabue et al, 2014) or >50% of the particulate Fe in phytoplankton and bacteria needs to be rapidly recycled. In the PZ, despite the darkness, grazing by the resident zooplankton community (e.g., Antarctic krill, Walsh et al, 2020) under the winter ice can lead to the coupled release of Fe and DOC potentially driving competition between bacteria and low-light acclimated ice algae, a community of phytoplankton not modeled in this study.…”

Antarctic krill fishery effects over penguin populations under adverse climate conditions: Implications for the management of fishing practices

“…Secondly, increased catches on years with low krill productivity decrease availability of krill to penguin populations. Krill population rises and falls from year to year, with potential recruitment cycles lasting 5 to 6 years (Reiss et al 2008), mostly driven by food competition (Ryabov et al 2017;Walsh et al 2020). Summer melting of sea ice accumulated during winter can boost local productivity in the WAP (Eveleth et al b, 2017a); therefore, during years of negative SAM (when winter sea ice cover is lower), krill could experience population limitation due to low availability of food and consequently low recruitment (i.e., Flores et al 2012;Meyer 2012).…”

Lipid content and stable isotopes of zooplankton during five winters around the northern Antarctic Peninsula

“…The U.S. AMLR Program conducted five winter surveys (August and September 2012–2016) around the northern Antarctic Peninsula aboard the U.S. National Science Foundation research vessel/ice breaker (RVIB) Nathaniel B. Palmer (Fig. 1 ) 19 . We surveyed a historical grid of 110 fixed stations located 20–40 km apart around the northern Antarctic Peninsula and South Shetland Islands, which was divided into four sampling areas: the Elephant Island Area (EI; 43,865 km 2 ), the South Area (the Bransfield Strait, SA; 24,479 km 2 ), the West Area (the west shelf immediately north of Livingston and King George Islands, WA; 38,524 km 2 ), and the Joinville Island Area (JI; 18,151 km 2 ).…”

“…Although not all species were sampled each year and, in some cases, the numbers of samples are small, At-sea sampling. Detailed methods for all at-sea sampling by the U.S. AMLR Program have been previously reported 19 . At each sampling station, we performed a Conductivity-Temperature-Depth (CTD) cast to 750 m or to within 10 m of the bottom in shallower areas (SBE9/11; Sea-Bird Electronics).…”