Abstract
Coralligenous reefs are characterized by large bathymetric and spatial distribution, as well as heterogeneity; in shallow environments, they develop mainly on vertical and sub-vertical rocky walls. Mainly diver-based techniques are carried out to gain detailed information on such habitats. Here, we propose a non-destructive and multi-purpose photo mosaicking method to study and monitor coralligenous reefs developing on vertical walls. High-pixel resolution images using three different commercial cameras were acquired on a 10 m2 reef, to compare the effectiveness of photomosaic method to the traditional photoquadrats technique in quantifying the coralligenous assemblage. Results showed very high spatial resolution and accuracy among the photomosaic acquired with different cameras and no significant differences with photoquadrats in assessing the assemblage composition. Despite the large difference in costs of each recording apparatus, little differences emerged from the assemblage characterization: through the analysis of the three photomosaics twelve taxa/morphological categories covered 97–99% of the sampled surface. Photo mosaicking represents a low-cost method that minimizes the time spent underwater by divers and capable of providing new opportunities for further studies on shallow coralligenous reefs.
Highlights
Photography represents an efficient and powerful way to disseminate scientific thoughts and findings both inside and outside the scientific community (Wilder 2009)
In the last thirty years, the number of studies using photography and video as methodologies for data collection has drastically increased in marine science; species, communities, and habitats can be advantageously investigated through these techniques for different scopes (Bicknell et al 2016; Durden et al 2016; Bayley and Mogg 2019)
Photomosaics in.tiff format were imported in ESRI ArcMap 10.2.2, where georeferencing and scaling routine were carried out as follows: two points placed 10 cm apart, acquired by real-time kinematic (RTK) GPS out of the water in real coordinates (WGS84, UTM fuse 32 N) were associated with two points in the photomosaic with the same linear distance (10 cm), which was measured in the picture by the 20 cm ruler placed in the scene
Summary
Photography represents an efficient and powerful way to disseminate scientific thoughts and findings both inside and outside the scientific community (Wilder 2009). This aspect is especially true when coralligenous reefs are found on vertical walls and overhangs In these complex habitats acoustic (multibeam and side-scan sonar) data derived from ship-based research surveys, ROVs, and Autonomous Underwater Vehicles (AUVs) cannot always provide exhaustive information at community level. Undisturbed coralligenous reefs are characterized by high small spatial scale patchiness which implies a considerable minimum sampling effort to characterize the structure of the assemblage at a given site (Kipson et al 2011; Piazzi et al 2004, 2016, 2017; Cecchi et al 2014; Casas-Guell et al 2016) In this framework, the application of a technique able to provide a detailed view of benthic assemblages with a relative time and cost efficiency will acquire a key role during the acquisition of ecological data and monitoring of such complex environments. The effectiveness of photomosaics, practical and theoretical advantages, opportunities, limitations, and challenges for future researches are discussed
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