Modeling environmental controls on the transport and fate of early life stages of Antarctic krill (Euphausia superba) on the western Antarctic Peninsula continental shelf

A one-dimensional, temperature-dependent model was used to simulate the descent―ascent cycle of the embryos and early larval stages of Antarctic krill to determine which regions of the western Antarctic Peninsula (wAP) continental shelf support successful completion of this cycle under present environmental conditions and those projected to occur as a result of climate change. The transport and fate of the embryo and larva under present and modified conditions was investigated with Lagrangian particle tracking simulations. The two modeling studies were implemented using temperature and density (embryo―larva model) and circulation distributions (Lagrangian particle tracking) obtained from a high resolution version of the Regional Ocean Modeling System configured for the wAP shelf region. Additional simulations used temperature and circulation distributions obtained from simulations that were forced with increased wind speed and increased transport of the Antarctic Circumpolar Current (ACC), both projected to possibly occur with climate change in the wAP region. Simulations using present conditions showed that successful completion of the descent-ascent cycle occurred along the outer shelf and on the shelf in regions with bottom depths of 600―700 m. Estimated residence times for the shelf regions that support success of the embryo and larva were 20-30 days. Thus, krill spawned in the mid and inner shelf regions can be retained in these regions through development to the first feeding stage (calyptopis 1). Increased winds and ACC transport resulted in more onshelf transport of Circumpolar Deep Water (CDW), which increased the volume of warm (1―1.5 °C) water at depth. These conditions supported a moderate increase in success of the krill embryo and larva, but only for limited areas of the shelf where hatching depths decreased by 10-30 m (< 5%) and development time to the calyptopis 1 stage decreased by 15―20%. The modified circulation conditions also supported increased advection of krill larvae into areas of the shelf that would experience the largest reduction of sea ice, especially in winter. Projected changes in wind strength and CDW transport may potentially enhance larval survival and advection onto the wAP shelf, but recruitment may be decreased by modifications to local sea ice distributions that would impede survival of Antarctic krill that overwinter on the shelf.