Overwintering of gelatinous zooplankton in the coastal Arctic Ocean

Jellyfish and ctenophore blooms are of increasing concern for human enterprise in marine waters, although bloom development remains poorly understood. A key factor in population dynamics of blooms is individual lifespan, which for most gelatinous zooplankton is assumed to be only a few months, often from spring to autumn. Accumulating evidence, however, indicates that some species may overwinter. In this study, we used video photography to quantify medusae and ctenophores beneath land-fast sea ice in the Chukchi Sea near Utqiaġvik (Barrow), Alaska, USA, from May to June, 2011–2014. Our data show large Chrysaora melanaster medusae overwintering near the bottom, which could contribute to multiyear population increases suggested for this species. C. melanaster medusae were observed dragging their tentacles along the bottom, possibly feeding on epibenthic macrofauna. This highlights an underappreciated mechanism for benthic–pelagic coupling by gelatinous zooplankton. Additionally, numerous individuals of 3 ctenophore and 1 hydrozoan species were seen primarily at the sea–ice interface rather than near the bottom. We hypothesize that overwintering of medusae and ctenophores under sea ice is favored by the continued availability of prey, related to high productivity in the coastal Arctic, including production by ice algae. Successful overwintering may also relate to physical sheltering and low water temperatures. Overwintering may be a common life-history trait for gelatinous zooplankton, with important implications for understanding annual and interannual population trends in many environments and has important implications for models including jellyfish and ctenophore populations and ecosystem dynamics.