Abstract
Abstract. This study presents a practical method to estimate dimensions of Paramuricea clavata colonies using generic photographic datasets collected across wide areas. Paramuricea clavata is a non-rigid, tree-like octocoral; this morphology greatly affects the quality of the sea fans multi-view stereo matching reconstruction, resulting in hazy and incoherent clouds, full of “false” points with random orientation. Therefore, the standard procedure to take measurements over a reconstructed textured surface in 3D space is impractical. Our method overcomes this problem by using quasi-orthorectified images, produced by projecting registered photos on the plane that best fits the point cloud of the colony. The assessments of the measures collected have been performed comparing ground truth data set and time series images of the same set of colonies. The measurement errors fall below the requirements for this type of ecological observations. Compared to previous works, the presented method does not require a detailed reconstruction of individual colonies, but relies on a global multi-view stereo reconstruction performed through a comprehensive photographic coverage of the area of interest, using a lowcost pre-calibrated camera. This approach drastically reduces the time spent working on the field, helping practitioners and scientists in improving efficiency and accuracy in their monitoring plans.
Highlights
Climate change is threatening underwater habitats worldwide
P. clavata has been subjected to important episodes of mass mortality that have caused a general reduction of its distribution on the upper bathymetric limit, and local extinctions across the Mediterranean Sea (Linares et al, 2007)
P. clavata presents all the characteristics to be considered an effective indicator of the impact of climatic anomalies on the coralligenous community (Linares et al, 2008) which represents one of the greater biodiversity hotspot habitat in the Mediterranean Sea (Ballesteros, 2006)
Summary
Climate change is threatening underwater habitats worldwide. The study of the growth, abundance, and recovery capability of those species provides valuable information on the conservation status of the entire habitat. In the Mediterranean Sea, the fans of the red gorgonian Paramuricea clavata (Risso, 1826) create complex seascapes and contribute to one of the richest temperate biogenic habitat: the coralligenous (Ballesteros, 2006). The intricate structure of the sea fans provide a shelter for many species at different life stages, attenuate the incidence of light and facilitate the growth of coralline algae. The red gorgonian is considered an ”engineer species”, as its growth helps building the structure of the seascape (Valisano et al, 2016). To develop conservation actions aiming at protecting coralligenous habitats, we require a comprehensive understanding of the resilience of the species
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