Abstract
The need for sound baseline information about community structure and composition against which changes can be detected and quantified is a well-recognised priority in Antarctica. Here, the collection of such data is challenging, especially at sea, where long-term monitoring is usually logistically feasible only in the proximity of permanent research stations. In recent years, underwater photogrammetry has emerged as a non-destructive and low-cost method for high-resolution topographic reconstruction. We decided to apply this technique to videos, recorded during standard SCUBA surveys of Antarctic benthos in Tethys Bay (Ross Sea, Antarctica) in 2006 and 2015 and originally not meant for photogrammetry. Our aim was to assess the validity and utility of the photogrammetric method to describe benthic communities from the perspective of long-term monitoring. For this purpose, two of the transects surveyed in 2015 were revisited in 2017. Videos were processed with photogrammetric procedures to obtain 3D models of the seafloor and inhabiting organisms. Overall, a total of six 20 m-long transects, corresponding to a total area of ~ 200 m2 of seafloor were analysed. Accuracy of the resulting models, expressed in terms of Length Measurement Error (LME), was 1.9 mm on average. The 2017 transects showed marked differences in some species, such as a 25–49% increase in the number of sea urchins Sterechinus neumayeri (Meissner, 1900) and the complete disappearance of some sponges Mycale (Oxymycale) acerata Kirkpatrick, 1907. Our analyses confirm the efficacy of photogrammetry for monitoring programmes, including their value for the re-analysis of legacy video footage.
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Acknowledgements
The Project "ICE-LAPSE" (PNRA 2013/AZ1.16: “Analysis of Antarctic benthos dynamics by using non-destructive monitoring devices and permanent stations”) was funded by the Italian National Antarctic Program. We are indebted to the Comando Subacquei ed Incursori (COMSUBIN) of the Italian Navy for help and assistance during the dives. This paper is a contribution to the SCAR-ANTOS Expert Group (https://www.scar.org/science/antos/home/). Some of geospatial procedures carried out during this study were performed at the Geo-technology Centre of University of Siena (www.geotecnologie.unisi.it) in the lab of Prof. R. Salvini. The collection of the 2006 and 2017 video recordings was funded by the NZ Ministry of Primary Industries and Ministry of Business, Innovation and Employment, respectively, and supported by Antarctica New Zealand and the excellent NIWA dive teams.
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Supplementary material 1 (TIFF 37166 kb) Online Resource 1. Photos recorded by S. Schiaparelli at the site “Zecca” (Tethys Bay, Terra Nova Bay) in previous underwater surveys, conducted in 2006- XXI PNRA Expedition, Boxes (a), (b) and (c)- and 2009- XXV PNRA Expedition, Box (d). These images depict small areas of the seafloor (the field of view is always approximately ≤ 1 m2) at similar depths of in the same area described in our study. Even they were not shot with the purpose of quantifying A. colbecki densities (they lack of an appropriate scale bar), they highlight how higher the number of specimens of this species was compared with 2015 and 2017 images. Box (a): A Dendrilla antarctica Topsent, 1905 surrounded by 8 A. colbecki specimens (7th February 2006, 22.9 m depth); Box (b): 5 specimens of A. colbecki in a small area of seafloor (21st January 2006, 22.9 m depth); Box (c): An Urticinopsis antarctica (Verrill, 1922) ‘hemmed in’ by more than 20 A. colbecki (31st January 2006, 26.8 m depth); Box (d): A massive Mycale acerata specimen with some A. colbecki aside (18th December 2009, 22,7 m depth).
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Piazza, P., Cummings, V., Guzzi, A. et al. Underwater photogrammetry in Antarctica: long-term observations in benthic ecosystems and legacy data rescue. Polar Biol 42, 1061–1079 (2019). https://doi.org/10.1007/s00300-019-02480-w
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DOI: https://doi.org/10.1007/s00300-019-02480-w