1. DFG PROJECT: SPP 1158 (JA-1063/17-1)
CLIMATE CHANGE IMPACTS ON ANTARCTIC BENTHOS: ECOLOGICAL IMPACTS OF PERMANENT ICE-SHELF COLLAPSE ON SPONGE COMMUNITIES
Gedeihen und Limitierung der Schwamm-Fauna des ehemaligen Eisschelfs Larsen AB
Rachel Downey · Senckenberg Frankfurt; Dorte Janussen · Senckenberg Frankfurt
Introduction
Regional warming in the western sector of the Antarctic has been observed since the 1950s. In 1995, this warming led to the collapse of the Larsen A ice-shelf, followed by the Larsen B ice shelf in Research expeditions in 2007, 2011, and 2013 were conducted by a multi-disciplinary team to track and monitor the ecological and oceanographic changes in this region, both from the former Larsen AB ice-shelves, but also from the still intact Larsen C ice-shelf and the adjacent Antarctic Peninsula (Gutt et al., 2010). Sponges play a key role in Southern Ocean benthic communities, important both for biomass and as habitat for many other organisms. Recent studies utilising ROV in this region have shown that glass sponges (Hexactinellida) have rapidly increased their abundance after ice-shelf collapse. This project aims to taxonomically identify all sponges collected in these expeditions to determine the biological diversity of these communities and how, during this time period, they have ecologically responded to the loss of permanent ice-shelves. Utilising all known sponge records from the Southern Ocean, faunal analyses will also be applied to understand the uniqueness of these former ice-shelf communities.
Methodology
The sponge material for this study was collected during 2006/7, 2011 and 2013 in the region of the former Larsen AB ice-shelves, Larsen C, Snow Hill and Dundee islands, and around the western sector of the Antarctic Peninsula by the R/V Polarstern (Map 1). Over 1,200 sponge specimens were collected at station depths between 109 and 889 m by Agassiz trawl (AGT), Beam trawl (BT) and Rauschert dredge (RD). These sponges are currently being identified, utilising the standard methodology in skeletal architecture and spicules (Boury-Esnault and Rützler,1997). Determination of the diversity and richness of these regional sponge communities will be the first step. Temporal analysis of sponge community changes at Larsen A and B since the ice-shelf break-up will form the second step in the process. Published sponge data from ROV (Remotely Operated Vehicle) analysis at one Larsen A transect (Fillinger et al. 2013) will be compared to trawled data from the same station to assess taxonomic, biomass and abundance changes. All previous sponge data from this region and the wider Southern Ocean will be used to assess regional sponge diversity, long-distance recruitment, and how unique regional faunal communities under the ice-shelf were before the break-up. A B
LARSEN A C D
Figures A-D: Larsen A preliminary analysis utilising new and published data. Figure A: Map A is the general location of the ROV Larsen A study site and Map B shows the Larsen area showing ice-shelf collapse; Map C shows the bathymetry; Map D shows the ROV and Agassiz trawls in this region. Figure B: Photo A indicates the ascidian dominance of 2007 transect; Photo B illustrates the glass-sponge dominance of the 2011 transect; Illustration C shows the abundance of each size class at 2007 (dashed line) and 2011 (green line), scale bar is 100 m. Figure C: shows the increase in numbers of species and genera at Larsen A from 2007 to Figure D: Graph A are the ROV abundances (mean ± standard error), and Graph B is the ROV size-frequency distribution (mean ± standard error). Figures A, B & D (Fillinger et al. 2013).
Preliminary Results
Larsen A: Two to three fold increase in glass sponge biomass and abundance, boom-bust cycles of hexactinellids, and an increase in sponge species and genera in time since ice-shelf collapse (Figures A-D). Rapid colonisation of sponges.
2007: 55% demosponges (3 gen., 4 spp.), 45% hexactinellids (3 gen., 4 spp.)
2011: 21% demosponges (5 gen., 5 spp.), 79% hexactinellids (2 gen., 6 spp.)
Larsen B: Invasion of pioneer Antarctic sponges: Stylocordyla spp., Homaxinella spp.
2007: 55% demosponges (10 gen., 13 spp.), 43% hexactinellids (5 gen., 9 spp.), 2% Calcarea (1 gen., 1 sp.)
2011: 55% demosponges (3 gen., 3 spp.), 44% hexactinellids (3 gen., 3 spp.), 11% Calcarea (1 gen., 1 sp.)
Larsen C: Typical deep-sea spp. and genera: Asbestopluma spp., Calycosoma spp. 2011: 23% demosponges (2 gen., 2 spp.), 77% hexactinellids (6 gen., 7 spp.)
Snow Hill & Dundee islands: these site indicate benthic disturbance, pioneer demosponge species found (Tetilla spp.), with few hexactinellids found.
2007: 81% demosponges (11 gen., 19 spp.), 19% hexactinellids (3 gen., 5 spp.)
Future Plans
Continuation of sponge identifications in the former Larsen ice-shelf region. Analysis of sponge fauna to determine regional differences and compare these to the wider Antarctic region. The goal is to achieve a greater understanding of the pre-Larsen AB break-up communities, how each of these communities have responded ecologically to ice-shelf collapse spatially and temporally, and to potentially use this information to predict future ecological impacts of Antarctic ice-shelf collapse on benthic ecosystems.
KEY
Red dots: all known pre-2006 sponge sampling stations (OBIS, 2014)
POLARSTERN STATIONS
Green dots: PS69 (2006/7)
Yellow dots: PS77 (2011)
Blue dots: PS81 (2013)
DUNDEE ISLAND
SNOW HILL ISLAND
LARSEN A
LARSEN B
LARSEN C
Map 1: Larsen shelf and West Antarctic Peninsula station data for sponges. Areas labelled are to be studied temporally and spatially for taxonomic and ecological changes.
References
Downey R. V., Griffiths H. J., Linse K. , Janussen, D Diversity and distribution patterns in high southern latitude sponges.- PLoS One, 7 (7), 1-16
Fillinger, L., Janussen, D., Lundälv, T., Richter, C Rapid glass sponge expansion after climate-induced Antarctic ice-shelf collapse. Current Biology, 23,
Gutt., J., Barratt, I., Domack., E., d’Udekem d’Acoz, C., Dimmler, W., Grémare, A., Heilmayer, O., Isla, E., Janussen., D., et al Biodiversity change after climate-induced ice-shelf collapse in the Antarctic. Deep-Sea Research II: doi: /j.dsr