3D Fine-scale Terrain Variables from Underwater Photogrammetry: A New Approach to Benthic Microhabitat Modeling in a Circalittoral Rocky Shelf

Elena Prado,Pilar Ríos,Augusto Rodríguez-Basalo,Francisco Sánchez,Adolfo Cobo

doi:10.3390/rs12152466

Abstract

The relationship between 3D terrain complexity and fine-scale localization and distribution of species is poorly understood. Here we present a very fine-scale 3D reconstruction model of three zones of circalittoral rocky shelf in the Bay of Biscay. Detailed terrain variables are extracted from 3D models using a structure-from-motion (SfM) approach applied to ROTV images. Significant terrain variables that explain species location were selected using general additive models (GAMs) and micro-distribution of the species were predicted. Two models combining BPI, curvature and rugosity can explain 55% and 77% of the Ophiuroidea and Crinoidea distribution, respectively. The third model contributes to explaining the terrain variables that induce the localization of Dendrophyllia cornigera. GAM univariate models detect the terrain variables for each structural species in this third zone (Artemisina transiens, D. cornigera and Phakellia ventilabrum). To avoid the time-consuming task of manual annotation of presence, a deep-learning algorithm (YOLO v4) is proposed. This approach achieves very high reliability and low uncertainty in automatic object detection, identification and location. These new advances applied to underwater imagery (SfM and deep-learning) can resolve the very-high resolution information needed for predictive microhabitat modeling in a very complex zone.

Highlights

Circalittoral rock substrates are characterized by very diffuse light and more constant hydrodynamic conditions than in the upper beds, the currents in some places can be strong
We present the resulting habitat mapping of three zones of the circalittoral zone dominated by different predominant species in each one
We provided evidence that using a SfM approach and terrain-derived variables at centimetric scales, predictive microhabitat models can be designed with very high confidence levels

Summary

Introduction

Circalittoral rock substrates are characterized by very diffuse light and more constant hydrodynamic conditions than in the upper beds, the currents in some places can be strong. The number of species characterizing these seafloors can be very high, depending on the different geographic areas, the geomorphology of the bottom and different factors that affect them [1]. The cup sponge (P. ventilabrum) and the yellow coral (D. cornigera) are the most representative structural species in the vulnerable habitat 1170 of the EU Directive [1] within the studied area. As for microscale, the Artemisina transiens sponge appears in abundance [3]. In this area the sponge communities make up 14.5% of coverage [4]. This variety of species in the same geographic location makes the area complex to map. It is even more difficult to carry out predictive habitat modeling studies because very detailed scales must be established

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