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

Abstract

Over 30% of the Antarctic continental shelf is permanently covered by floating ice shelves, providing aphotic conditions for a depauperate fauna sustained by laterally advected food. In much of the remaining Antarctic shallows (<300 m depth), seasonal sea-ice melting allows a patchy primary production supporting rich megabenthic communities dominated by glass sponges (Porifera, Hexactinellida). The catastrophic collapse of ice shelves due to rapid regional warming along the Antarctic Peninsula in recent decades has exposed over 23,000 km(2) of seafloor to local primary production. The response of the benthos to this unprecedented flux of food 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. 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, suggest that Antarctic hexactinellids, locked in arrested growth for decades, 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.

Mapping Antarctic Suspension Feeder Abundances and Seafloor Food-Availability, and Modeling Their Change After a Major Glacier Calving

“…Particularly strong changes are predicted in the horizontal flux of food particles post-calving, which is important in determining the distribution of suspension feeders . Similar to other Antarctic regions that have recently become ice-free (e.g., Fillinger et al, 2013), our results suggest environmental conditions on the Mertz Bank now are much more favorable for suspension feeders (SFs) than before the calving. Our modeling suggests that there will be a strong, but locally confined increase in SF-abundance on the Mertz Bank of up to 40%.…”

“…The MGT is thought to calve massive icebergs in a ∼70 year cycle (Campagne et al, 2015;Giles, 2017), meaning that there are likely also differences in the long-term stability of environmental conditions, and in the frequency of iceberg-scour between the Mertz Bank near the MGT and the Adélie Bank in the West of the George V shelf. Studies on the West Antarctic Peninsula suggest that at least some components of Antarctic benthic communities on the shelf, such as glass sponges and pioneering species, can increase rapidly in areas that are newly ice-free, fueled by higher export of surface production (Gutt et al, 2011;Fillinger et al, 2013). Conversely, slower-growing deep-sea corals and bryozoans may respond more slowly to changing environmental conditions.…”

“…Seafloor communities represent the richest component of Antarctic biodiversity (Griffiths, 2010), are highly endemic (Griffiths et al, 2009), and play an important role in the marine ecosystem (Thurber et al, 2014). However, despite evidence that a changing environment influences the distribution of these communities (Gutt et al, 2011(Gutt et al, , 2013Fillinger et al, 2013;Griffiths et al, 2017), no study has so far quantified and mapped how their distribution might change due to a changing icescape at the ocean surface. One of the reasons for the lack of quantitative studies is that although surface-derived food is one of the main drivers, it is only recently that the nature and strength of this relationship has been quantified on the Antarctic shelf using a so-called Food-Availability-Model (FAM) .…”

Seabed images versus corer sampling: a comparison of two quantitative approaches for the analysis of marine benthic communities in the southern Weddell Sea (Southern Ocean)

“…In the Weddell Sea and off the Antarctic Peninsula, benthic communities have been studied by means of both corers (e.g., Gerdes et al 1992Gerdes et al , 2003Gerdes et al , 2008Sañé et al 2012) and seabed imaging (e.g., Gutt and Piepenburg 2003;Gutt et al 2011Gutt et al , 2013Fillinger et al 2013). Despite the fact that these methods complement each other, studies using both approaches in a comparative manner are scarce.…”

The influence of the geomorphological and sedimentological settings on the distribution of epibenthic assemblages on a flat topped hill on the over-deepened shelf of the western Weddell Sea (Southern Ocean)

“…Because of the extremely slow growth of large glass sponges and also some demosponges (Dayton, 1989;Dayton et al, 2013), such communities, if mainly composed of large specimens, are indicators of long-term environmental stability. However, it has been shown that populations of ascidians and ophiuroids (Gutt et al, 2013a), young hexactinellid sponges (Fillinger et al, 2013;Gutt et al, 2012) as well as generally fast-growing demosponges known for their highly dynamic performance (Gutt et al, 2012), including reproduction, recruitment, growth and mortality, can also occur in the same area. Since we know that almost everywhere on the "normal" Antarctic shelf, albeit with different proportions, two community supra-types (those dominated by epifaunal suspension feeders and those dominated by infaunal or vagrant deposit feeders) coexist, we can assume that this can also be applied to the area of this study.…”