Disturbance, colonization and development of Antarctic benthic communities

Abstract

A decade has yielded much progress in understanding polar disturbance and community recovery-mainly through quantifying ice scour rates, other disturbance levels, larval abundance and diversity, colonization rates and response of benthos to predicted climate change. The continental shelf around Antarctica is clearly subject to massive disturbance, but remarkably across so many scales. In summer, millions of icebergs from sizes smaller than cars to larger than countries ground out and gouge the sea floor and crush the benthic communities there, while the highest wind speeds create the highest waves to pound the coast. In winter, the calm associated with the sea surface freezing creates the clearest marine water in the world. But in winter, an ice foot encases coastal life and anchor ice rips benthos from the sea floor. Over tens and hundreds of thousands of years, glaciations have done the same on continental scales-ice sheets have bulldozed the seabed and the zoobenthos to edge of shelves. We detail and rank modern disturbance levels (from most to least): ice; asteroid impacts; sediment instability; wind/wave action; pollution; UV irradiation; volcanism; trawling; non-indigenous species; freshwater inundation; and temperature stress. Benthic organisms have had to recolonize local scourings and continental shelves repeatedly, yet a decade of studies have demonstrated that they have (compared with lower latitudes) slow tempos of reproduction, colonization and growth. Despite massive disturbance levels and slow recolonization potential, the Antarctic shelf has a much richer fauna than would be expected for its area. Now, West Antarctica is among the fastest warming regions and its organisms face new rapid changes. In the next century, temperature stress and non-indigenous species will drastically rise to become dominant disturbances to the Antarctic life. Here, we describe the potential for benthic organisms to respond to disturbance, focusing particularly on what we know now that we did not a decade ago.

Figure 1

Schematic of wind, wave and ice disturbance with latitude and depth. (a) Wind and wave plot modified from Barnes (2002). (b) Ice disturbance data are estimates based on Dayton (1990), Barnes (1999), Gutt & Piepenburg (2003), Brown et al. (2004) and references therein.

Figure 2

Ice foot on the shore of Ross Island in McMurdo Sound. Photo by K. E. Conlan ©1996, Canadian Museum of Nature.

Figure 3

Anchor ice at McMurdo Sound. When the anchor ice becomes buoyant, it rips off the surface seabed (right). Photo by K. E. Conlan ©1996, Canadian Museum of Nature.

Figure 4

Scour paths criss-cross the (a) Arctic and (b) Antarctic seafloors. (a) Multibeam image of the seabed in the Beaufort Sea, Canadian Arctic, courtesy of S. Blasco, Geological Survey of Canada. The ice scours are created by pressure ridges and multiyear sea ice. (b) Sun-illuminated image of multibeam echosounder data captured at Cape Hallett, Western Ross Sea, Antarctic by NIWA's research vessel Tangaroa during January 2001. (c) and (d) Detailed close-ups showing scouring within main image. Sourced from LINZ Cape Adare, Cape Hallett and Possession Islands Hydrographic Survey: Crown copyright reserved.

Figure 5

Undersurface of an iceberg grounded in McMurdo Sound showing ‘dropstones’ which may be released thousands of kilometres away as the iceberg drifts and melts. Photo by K. E. Conlan ©1996, Canadian Museum of Nature.

Figure 6

Hypoxic black pool in an ice scour depression on the seafloor of Resolute Bay, Cornwallis Island in the Canadian High Arctic. The surface of the pool is covered by a mist of white bacteria. Photo by K. E. Conlan ©1996, Canadian Museum of Nature.

Figure 7

Sea temperatures around Antarctica from (a) charge-transfer device and (b) remote sensed data. The symbols are maximum (filled) and minimum (open), Southern Ocean (squares) and South Atlantic (circles) sites. Data from Barnes et al. (2006) and references therein.

Figure 8

Highly seasonal (and sequential) recruitment by cheilostome bryozoans at Adelaide island (WAP), 2001–2003. Key to species symbols on plot. y-axis values are scaled for maxima and minima of each species, so are relative; hence no units are shown. Data from Bowden (2005).

Figure 9

Early community development on artificial hard substratum. Settlement panels from Adelaide Island (WAP) at 1 (figure 9a) and 3 (figure 9b) years underwater and from Casey Station (Budd Coast, East Antarctica) at 1 (figure 9c) and 3 (figure 9d) years underwater. Photos by D. Bowden ©2005 and J. Stark ©2005.

Figure 10

Polychaete zonation, for selected species, within an anchor ice gradient adjacent to McMurdo Station (n=6); data from Lenihan & Oliver (1995) and Conlan et al. (2004).

Figure 11

Rich benthos at shallow water at 20 m at Rothera, Adelaide Island, WAP (main photo) and at Signy Island, Scotia Arc (insert). Main Photo by D. Smale ©2005 and insert by D.K.A. Barnes ©1993.