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.
Highlights
Ecological studies focusing on marine benthic communities have received a breakthrough from the application of a variety of non-destructive sampling and mapping techniques
We present an investigation on diveroperated photogrammetry for the description of shallow-water rocky-bottom benthic communities in Antarctica
The inclusion of oblique images from the two lateral strips has proved to ameliorate the results of the self-calibrating BA, thanks to a better estimate of interior orientation parameters of video transects not designed for photogrammetry
Summary
Ecological studies focusing on marine benthic communities have received a breakthrough from the application of a variety of non-destructive sampling and mapping techniques. The availability of affordable (and often open-source) software to process and analyse the images have pushed the popularity of 3D image-based modelling approaches Overall, these techniques provide low-impact and cost-effective methodologies that enable the observation of natural processes with the lowest possible disturbance on communities and organisms coupled with a higher efficiency and methodological reliability in the analyses. These techniques provide low-impact and cost-effective methodologies that enable the observation of natural processes with the lowest possible disturbance on communities and organisms coupled with a higher efficiency and methodological reliability in the analyses Due to these reasons, 3D imaging techniques have been considered as suitable tools in the scientific community to study fragile, slow growing and potentially endangered environments, such as coral reefs or Antarctic benthic communities. To train people from different application fields to properly record the images best suited for 3D modelling of underwater environments is still an open issue
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