Recent advances in underwater imaging technology allow for the
gathering of invaluable scientific information on seafloor ecosystems, such as
direct in situ views of seabed habitats and quantitative data on the
composition, diversity, abundance, and distribution of epibenthic fauna. The
imaging approach has been extensively used within the research project DynAMo
(Dynamics of Antarctic Marine Shelf
Ecosystems) at the Alfred Wegener Institute, Helmholtz
Centre for Polar and Marine Research Bremerhaven (AWI), which aimed to
comparatively assess the pace and quality of the dynamics of Southern Ocean
benthos. Within this framework, epibenthic spatial distribution patterns
have been comparatively investigated in two regions in the Atlantic sector
of the Southern Ocean: the shelf areas off the northern tip of the Antarctic
Peninsula, representing a region with above-average warming of surface
waters and sea-ice reduction, and the shelves of the eastern Weddell Sea as
an example of a stable high-Antarctic marine environment that is not (yet)
affected by climate change. The AWI Ocean Floor Observation System (OFOS)
was used to collect seabed imagery during two cruises of the German
research vessel
The research project Dynamics of Antarctic Marine Shelf Ecosystems (DynAMo) at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research Bremerhaven (AWI) aimed to comparatively assess the pace and quality of the dynamics in Southern Ocean benthos and endotherms. It is a contribution to the international scientific research program Antarctic Thresholds – Ecosystem Resilience and Adaptation (AnT-ERA) of the Scientific Committee on Antarctic Research (SCAR). By applying a comparative field study approach, the geographical focus of DynAMo was on an area with above-average warming of surface waters and sea-ice reduction around the tip of the Antarctic Peninsula (Gutt, 2013; Gutt et al., 2016) and a stable high-Antarctic marine environment that is not (yet) affected by climate change in the southeastern Weddell Sea (Schröder, 2016).
The Ocean Floor Observation System (OFOS) of the Alfred Wegener
Institute (AWI), Helmholtz Centre for Polar and Marine Research Bremerhaven,
deployed from the RV
Special emphasis has been on the study of the spatial distribution patterns of shelf megabenthic epifauna. According to an often-used pragmatic definition proposed by Gage and Tyler (1991), this seabed community fraction is comprised of all organisms that are large enough to be visible in seabed images and/or to be caught by towed sampling gear (i.e., organisms with body sizes larger than approximately 1 cm). They are of ecological significance for Southern Ocean shelf ecosystems (Gutt, 2006), as they affect the small-scale topography of seafloor habitats and hence the structure of the entire benthic community (Gili et al., 2006). In addition, some megabenthic species are sensitive to environmental change due to their slow growth, specific reproduction mode, high degree of environmental adaptation, and narrow physiological tolerances, and can thus serve as early indicators of ecosystem shifts in response to environmental change (Barnes et al., 2009).
Based on several investigations performed during previous cruises of the
German research vessel to complement surveys of mega-epibenthic assemblages on the shelf off the
northern Antarctic Peninsula (cruise PS81 2013) and the southeastern
Weddell Sea (cruise PS96 2015–2016), providing further data that are comparable with
those obtained in earlier studies in these regions (Biebow et al., 2014); to identify the spatial distribution patterns of epibenthic megafauna across
multiple spatial scales (10 m, 100 m, 10 km, and 100 km); and to contribute to the standardization of the classification of Antarctic
megabenthic communities (Gutt, 2007, 2013).
Seabed images are used for different purposes. These include (1) assessing the large
epibenthos as a whole, (2) carrying out quantitative community and diversity
analyses, (3) including environmentally relevant (e.g., CTD data if CTD
sensors are integrated in OFOS) and visible seabed parameters (e.g., the amount
of gravel and debris and the number of ripple marks) at exactly the same spots from which the
biological information originates, (4) allowing for analyses with high spatial
resolution (patterns within and between adjacent photographs, e.g., to survey
the impact of iceberg scouring), and (5) acquiring information on biological
interactions, such as epibiotic life mode.
The AWI Ocean Floor Observation System (OFOS) was used for seabed
imaging surveys along drift profiles (transects) to investigate the
epibenthic megafauna and its seafloor habitats. The setup and mode of
deployment for OFOS was similar to that described by Bergmann and Klages
(2012). OFOS is surface-powered gear (Fig. 1) equipped
with two downward-looking cameras installed side by side: a high-resolution,
wide-angle still camera (Canon®EOS 5D Mark
III with
EF 24 f/1.4L II lens, f-stop 13, exposure time
The system was vertically lowered over either the starboard side (PS81) or
the stern of the ship (PS96) with a broadband fiber-optic cable until it
hovered approximately 1.5 m above the seabed. It was then towed after the
slowly sailing ship at a speed of approximately 0.5 kn (0.25 m s
According to the manufacturer specifications, the GPS receiver of the
List of stations at which the Ocean Floor Observation System (OFOS)
was deployed during
Map of the geographic positions of the stations at which seabed
photographs were taken by means of OFOS along photographic transects in
three regions (Weddell Sea, Bransfield Strait, and Drake Passage) off the
northern Antarctic Peninsula during
Example of a seabed photo taken during
List of stations at which the AWI Ocean Floor Observation System (OFOS)
was deployed during
Maps showing the geographic positions of OFOS stations in the
Weddell Sea during
During the profile, OFOS was kept hanging at the preferred height above the seafloor by means of the live video feed and occasional minor cable length adjustments with the winch to compensate for small-scale bathymetric variations in seabed morphology. Information on water depth and height above the seafloor were continuously recorded by means of OFOS-mounted sensors (POSIDONIA transponder in 2013, GAPS transponder in 2015–2016, Tritech altimeter during both PS81 and PS96).
Three lasers, which are placed beside the still camera, emit parallel beams and project red light points arranged as an equilateral triangle with a side length of 50 cm in each photo. This provides a scale that can be used to calculate the seabed area depicted in each image and/or measure the size of organisms or seabed features visible in the image. In addition, the seabed area depicted was estimated using altimeter-derived height above seafloor and optical characteristics of the OFOS still camera.
In automatic mode, a seabed photo depicting an area of approximately 3.45 m
Example of photographic material gathered during
Within the context of the overall ecological DynAMo working program, OFOS
was used to collect seabed imagery during two cruises of the RV
During cruise PS81, OFOS was successfully deployed at a total of 31 stations at water depths between 29 and 784 m (Table 1), delivering a total of more than 15 000 seabed photos (Gutt, 2013). At most stations, series of 500 to 530 pictures were taken along transects approximately 3700 m (2 nautical miles) in length during net wire times (with OFOS at the bottom) of 4 h per transect. At some stations, OFOS had to be deployed for shorter periods of time due to high wave heights and strong winds.
The stations were placed in three regions off the Antarctic Peninsula
between 61 and 64
Figure 3 is an example of a seabed photo taken at station PS81/110, showing rich megabenthic epifauna (e.g., abundant ascidians and a swarm of demersal nototheniid fish) on the shelf off Joinville Island in the eastern Bransfield Strait at 212 m of water depth on 26 January 2013.
During cruise PS96, OFOS was deployed at a total of 13 stations at water depths between 200 and 750 m (Table 2). During the casts with 54 min to 2 h 14 min of on-ground duration, series of 110 to 293 photos (2670 in total) were obtained along OFOS transects 0.9 to 2.6 km in length. In addition, a total of more than 14 h 50 min of video footage (available from the first author on request) was recorded.
OFOS stations were distributed over several regions in the southeastern and
southern Weddell Sea (Fig. 4). (1) Off Austasen, one transect (PS96/001) was
positioned in close vicinity to the BENDEX sites investigated in 2003, 2011,
and 2014 (Biebow et al., 2014). Unfortunately, the actual main BENDEX
location, artificially disturbed in 2003, could not be revisited, since
it was located under fast ice and hence not accessible in December 2015.
(2) Four stations (PS96/026, 027, 037, and 048) were located in the main
study area of the PS96 cruise, which is the broad shelf of the southern Weddell Sea
west of Filchner Trough. (3) Five stations (PS96/007, 008, 010,
057, and 061) were situated on the shelf east of Filchner
Trough. Some of these stations were revisits of sites that had been
investigated during
As an example of prominent epibenthic megafauna recorded in seabed photos taken during PS96, see Fig. 5, which shows a compilation of organisms photographed at station PS96/090 on the shelf off the Riiser-Larsen Ice Shelf (Rampen) at water depths from 265 to 310 m on 29 January 2016.
All images taken during the two cruises, including metadata, are available
from the data publisher PANGAEA (Piepenburg et al., 2013, for PS81;
Piepenburg, 2016, for PS96). Images are listed with a georeference and time
for each transect in single-child datasets. All transects for each cruise are
grouped in a parent dataset (PS81:
An example for a scientific study based on the analyses of the seabed images, the collection of which are reported here, is an investigation of the composition and distribution patterns of the epibenthic ascidian fauna on the shelves off the Antarctic Peninsula (Segelken-Voigt et al., 2016b). The supplementary information used in this study, including environmental data, is also available from PANGAEA (Segelken-Voigt et al., 2016a). A second example is the investigation of the influence of geomorphological and sedimentological settings on the distribution of epibenthic assemblages on
the Nachtigaller Shoal, a flat-topped submarine hill at the over-deepened shelf of the western Weddell Sea discovered during the PS81 cruise in 2013 (Dorschel et al., 2014).
The authors declare that they have no conflict of interest.
We would like to thank the HGF-MPG Joint Research Group for Deep-Sea Ecology and
Technology at the Alfred Wegener Institute, Helmholtz Centre for Polar and
Marine Research Bremerhaven, for providing access to OFOS during