Rapid Glass Sponge Expansion after Climate-Induced Antarctic Ice Shelf Collapse

Over 30% of the Antarctic continental shelf is permanently covered by floating ice shelves [1], providing aphotic conditions [2, 3] for a depauperate fauna sustained by laterally advected food [4, 5]. In much of the remaining Antarctic shallows (<300 m depth), seasonal sea-ice melting allows a patchy primary production supporting rich megabenthic communities [6, 7] dominated by glass sponges (Porifera, Hexactinellida) [8-10]. The catastrophic collapse of ice shelves due to rapid regional warming along the Antarctic Peninsula in recent decades [11] has exposed over 23,000 km(2) of seafloor to local primary production [12]. The response of the benthos to this unprecedented flux of food [13] is, however, still unknown. In 2007, 12 years after disintegration of the Larsen A ice shelf, a first biological survey interpreted the presence of hexactinellids as remnants of a former under-ice fauna with deep-sea characteristics [14]. Four years later, we revisited the original transect, finding 2- and 3-fold increases in glass sponge biomass and abundance, respectively, after only two favorable growth periods. Our findings, along with other long-term studies [15], suggest that Antarctic hexactinellids, locked in arrested growth for decades [8, 16], may undergo boom-and-bust cycles, allowing them to quickly colonize new habitats. The cues triggering growth and reproduction in Antarctic glass sponges remain enigmatic.