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Wintertime grazing rates of Antarctic krill, Euphausia superba, along the Northern Antarctic Peninsula

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https://ir.library.oregonstate.edu/concern/defaults/3j3334033

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  • Over 70% of the Antarctic krill population exists along the Antarctic Peninsula, a region undergoing rapid climate change. Recent studies have shown a clear correlation between krill recruitment each spring and the timing and coverage of sea ice the winter before, with less sea ice and a shorter duration being cited as a threat to krill populations. It has been suggested that the larval stage (known as furcilia) of the Antarctic krill life cycle depends on sea ice and the algal communities growing in the ice for its overwinter survival. Given logistical challenges, relatively few studies have been conducted on Antarctic krill during the wintertime. The aim of this study was to investigate the grazing rates of Antarctic krill on algal biomass (either phytoplankton or ice algae) during the winter. We hypothesized that (1) grazing rates would be highest in areas of lower latitude (more sunlight) and in regions with highest percent sea ice coverage; and (2) furcilia would graze relatively more algal biomass than juvenile and adult krill. Antarctic krill were collected using a standard Isaac-Kidd Midwater Trawl (IKMT) net during the U.S. Antarctic Marine Living Resources (AMLR) Program’s research expedition to the northern Antarctic Peninsula in August of 2015. Grazing rates were estimated using the gut fluorescence technique. Highest grazing rates occurred in areas with 100% first year ice coverage, suggesting that krill feed on the phytoplankton and algal biomass associated with sea ice. We also found that grazing rates were higher at northern stations, confirming the role of latitude. While grazing rates of furcilia were significantly lower than those of juvenile and adult krill, when we converted grazing rates per individual to grazing rates per gram of body weight, we found that furcilia consumed the most by body weight. This finding supports studies claiming that sea ice plays a critical role in providing habitat and food for Antarctic krill, particularly furcilia. If winter sea ice continues to decline, the Antarctic krill population will be negatively impacted, with consequences for the community structure and food webs of the Southern Ocean ecosystem.
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  • Corvallis, Oregon, USA
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  • This research was funded in part by Oregon State University and the URSA Engage Award, and a donation from the G. Unger Vetlesen Foundation.
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