Benthic community patterns in Antarctic waters and along latitudes in the southern hemisphere
Staff
Collaboration
Dr. T. Brey, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany
Dr. A. Montiel, Universidad de Magallanes, Pta. Arenas, Chile
Dr. E. Quiroga, Escuela de Ciencias del Mar. Pontificia Universidad Católica de Valparaíso, Chile
Outreach
- Impact of iceberg scouring on macrobenthic communities in the high-Antarctic Weddell Sea
- Response of Antarctic benthic communities to disturbance: First results from the artificial Benthic Disturbance Experiment on the eastern Weddell Sea Shelf, Antarctica
- Polychaete assemblages on the Magellan and Weddell Sea shelves: comparative ecological evaluation
- The Antarctic-Magellan connection: Macrobenthos ecology on the shelf and upper slope, a progress report
- Spatial and temporal variability of the benthic assemblages associated to the holdfasts of the kelp Macrocystis pyrifera in the Straits of Magellan
Biodiversity patterns in benthic communities of the Southern Ocean
Our studies of benthic communities in the Southern Ocean extend over several latitudes and consider the high Antarctic Weddell Sea, especially the shelf and slope, and the benthos around the Peninsula area, the Scotia Arc and the southern tip of South America.
To many people the seafloor on the Antarctic shelves appears as a marine ecosystem with largely constant environmental conditions and comparatively low biotic and abiotic disturbance. In fact seasonal temperature fluctuations are incredibly low in some areas, salinity is fairly constant and imput of freshwater is negligible. However, despite these facts the high Antarctic benthic realm is subject to considerable disturbance, as has been shown by many investigations of AWI biologists in the last decades. Ice plays a prominent role as a disturbing agent and affects the biotic and abiotic realm alike. Disintegrating ice shelves and calving icebergs impact high Antarctic macrobenthic communities dramatically and make distribution patterns extremely heterogeneous. Iceberg scouring is one of the five most significant impacts on any ecosystem on earth and it also plays a key role in structuring recent Antarctic shelf benthos communities.
Effects of grounding icebergs on benthic shelf communities
Iceberg strandings occur regularly on the shallow Weddell Sea shelf and they play a substantial role in structuring benthic communities. They locally wipe out benthic communities and create open space for pioneer species to initiate recolonisation of such devastated areas. This creates a patchwork of different successional stages all of which increase the biodiversity in the benthic realm.
Even today we have a problem to place different successional stages into an absolute temporal sequence, because the exact dating of the disturbance event normally is unknown. The time scales of recolonisation after disturbance as well as patterns in the biodiversity, however, are considered as important questions, because both are strongly related to the vulnerability and resilience of these cold water systems.
Benthic community before and after artificial disturbance (BENDEX). Photo: E. Isla ICM - CSIC, Spain
In 2003 we started on the eastern Weddell Sea shelf the long-term benthic disturbance experiment BENDEX, which simulates the impact of grounding icebergs on the shelf community. By means of 11 densely-placed hauls with a modified bottom-trawl, a seabed area of appr. 100 x 1000 m was artificially scoured to inflict a similar damage to the benthic habitat as a grounding iceberg. Invertebrate benthic biomass was drastically reduced by a factor of 10 and the effects also became evident in the composition of the fauna. With this experiment we can follow the different successional stages of recolonisation and place them into an absolute temporal sequence, because - in contrast to former studies - we know the exact dating of the disturbance event. The BENDEX location will be revisited in 2011.
Large scale biodiversity patterns in benthic communities
Since 1987 nine expeditions with RV `POLARSTERN´ yielded the largest set of macrofauna samples collected so far in Antarctic waters. A total of 1013 samples were collected with a multibox corer at 178 stations from the Lazarev Sea in the east to the waters around the Antarctic Peninsula, covering a depth range from 170 to 4293 m.
Additional 125 samples collected with van Veen grabs and Reineck box corers at 69 stations early in the 1980s complete this large data base.
Sampling effort with the quantitative multibox corer. Photo: E. Isla ICM - CSIC, Spain
The benthic communities differed among regions in terms of biomass, abundance and composition of the fauna. Abundance and biomass values are characterized in all regions by a wide range of values (few hundred specimens to > 10,000 ind. m-2 and < 1 g wet weight to locally >1,000 g wet weight m-2).Comparably variable occurred the benthic densities and biomasses in the Patagonian channel and fjord system, but both did not show any significant statistical differences between the South American and Antarctic regions.
Diverse three-dimensional suspension feeder community. Photo: E. Isla ICM - CSIC, Spain
Contrasting the faunistic composition showed clear latitudinal differences. On the high Antarctic Weddell Seas shelf sponges, bryozoans, and gorgonarians can completely cover the seafloor, building up a typical three-dimensional multi-stored benthic habitat, which is colonized by extremely rich mostly epibenthic communities.
Typical but impoverished fauna in the LARSEN B embayment. Photo: E. Isla, ICM - CSIC, Spain
In the waters around the Peninsula the community structuring taxa dominating on the southeastern Weddell Sea shelf lost importance and polychaetes, echinoderms, crustaceans, and molluscs replaced them. The composition of the Magellan benthic fauna reflects the enormous habitat heterogeneity in the Magellan region and shows striking differences as compared to the Antarctic communities. Especially crustaceans gained importance due to the reptant decapods, which normally occur only occasionally south of the Antarctic convergence. Molluscs, too, gained importance in the Magellan region, whereas differences in the species inventories of polychaetes and echinoderms were less pronounced.
