Demographic and maturity patterns of Antarctic krill ( Euphausia superba ) in an overwintering hotspot
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ORIGINAL PAPER
Demographic and maturity patterns of Antarctic krill (Euphausia superba) in an overwintering hotspot Christian S. Reiss1 · Jefferson T. Hinke1 · George M. Watters1 Received: 12 September 2019 / Revised: 5 May 2020 / Accepted: 17 June 2020 © This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2020
Abstract Overwinter environmental conditions are a major driver of larval survival, recruitment, and reproductive pre-conditioning in Antarctic krill (Euphausia superba). Few winter studies exist from which to infer impacts of changing environmental conditions on the biology of krill. Here demographic and maturity patterns of krill during five winters are examined at an overwintering hotspot in the northern Antarctic Peninsula. Two different recruitment pulses were present over the 5 years of the study. A large recruitment event was evident in winter 2012, followed by cohort growth tracked through winter 2014. A recruitment event also occurred in 2015, despite lower abundance of larvae in 2013 and 2014. The recruitment pulse in 2015 was correlated with the intrusion of high salinity water, characteristic of the Weddell Sea, during a positive El Niño– Southern Oscillation phase, suggesting recruitment was driven by advection of recruits into the northern Antarctic Peninsula. Despite the inter-annual environmental variability, most female krill were in resting reproductive stages in all years. The lack of variability in female reproductive status during winter may impose a developmental constraint to earlier spawning than previously considered; the time necessary to advance from resting stages to reproductive maturity may limit the ability of krill to adapt to trends in the timing and magnitude of the spring bloom. The observed patterns of recruitment and variation in maturity stages highlight the complexity of krill population dynamics and should be considered when projecting population responses of Antarctic krill to climate-driven changes in the Southern Ocean. Keywords Antarctic krill · Recruitment · Maturity · Climate change · ENSO
Introduction The northern Antarctic Peninsula ecosystem is a critical region of the Southern Ocean for populations of Antarctic krill (Euphausia superba; hereafter krill) serving as a major spawning and recruitment area (Siegel and Watkins 2016) and as an overwintering hotspot, especially within Bransfield Strait (Reiss et al. 2017). Over the last 40 years, climatedriven changes have resulted in warming waters (Swart et al. 2018), declines in seasonal sea ice extent and duration (Stammerjohn et al. 2008, 2012), changing phytoplankton community structure from large diatoms to smaller cryptophytes during summer (Montes-Hugo et al. 2009), and have driven a southward shift in primary production (Schofield * Christian S. Reiss [email protected] 1
Antarctic Ecosystem Research Division, Southwest Fisheries Science Center, NOAA Fisheries, 8901 La Jolla Shores Dr, La Jolla, CA 92037, USA
et al. 2010, 2018).
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