Quantifying the response of structural complexity and community composition to environmental change in marine communities

Abstract

Habitat structural complexity is a key factor shaping marine communities. However, accurate methods for quantifying structural complexity underwater are currently lacking. Loss of structural complexity is linked to ecosystem declines in biodiversity and resilience. We developed new methods using underwater stereo-imagery spanning 4 years (2010-2013) to reconstruct 3D models of coral reef areas and quantified both structural complexity at two spatial resolutions (2.5 and 25 cm) and benthic community composition to characterize changes after an unprecedented thermal anomaly on the west coast of Australia in 2011. Structural complexity increased at both resolutions in quadrats (4 m(2)) that bleached, but not those that did not bleach. Changes in complexity were driven by species-specific responses to warming, highlighting the importance of identifying small-scale dynamics to disentangle ecological responses to disturbance. We demonstrate an effective, repeatable method for quantifying the relationship among community composition, structural complexity and ocean warming, improving predictions of the response of marine ecosystems to environmental change.

Quantifying Multiscale Habitat Structural Complexity: A Cost-Effective Framework for Underwater 3D Modelling

“…Additionally, the validation analyses showed accuracies ranging from 79% (reefscape) to 90% (coral colony), in agreement with previous studies assessing accuracies for photogrammetric measures of coral colonies [28,31,43,[66][67][68]. These results show evidence of the utility of this framework to coral reef ecology and monitoring, in particular given the rapid degradation of coral reefs worldwide, for example they could enable the monitoring of coral reef flattening after a bleaching event [69]. While recent photogrammetric studies have shown similar accuracies, worthy of highlighting is the capacity of this framework to quantify 3D metrics of habitat structural complexity from historical data, captured by off-the-shelf monocular cameras without reference objects present in the scene.…”

“…The larger extent examples presented in this study (reef scape and transect) stress the opportunity to test the long settled paradigm of reef flattening as a result of massive coral bleaching [7,77,78]. In fact, a similar approach, yet using significantly more expensive tools, recently unveiled evidence of a significant increase in reef structural complexity as a result of massive coral bleaching in Western Australia [69].…”

How Reliable Is Structure from Motion (SfM) over Time and between Observers? A Case Study Using Coral Reef Bommies

“…Previous studies have used structure from motion techniques to obtain measurement data from coral reefs [12,36,37], and while some studies have quantified measurement error in relation to 'true volume/surface area' as determined by laser scanning or traditional methods [10,13], no attempt to verify whether the measurements obtained using structure from motion were reproducible until now. Volume and surface area are basic measurements, and the implications of this study should also apply to studies that assess rugosity or other structural characteristics using this technique [9,11,50].…”

“…While such survey techniques are effective, they are limited by the precision of their measurements and the ease of directly comparing data from successive years or months. Recently, structure from motion has become prevalent as another tool for reef monitoring [8][9][10][11]. Structure from motion is an image processing technique that allows construction of accurate 3D models from overlapping successive photographs taken at various angles.…”

DocuScooter: An Innovative Underwater Scooter add-on for Scuba Diving and Citizen Science

“…What the marine community is lacking is an integrated system where all the processes of acquisition, processing, analysis and output representation are gathered in a unique solution. In literature there are different examples about improving the collection or the analysis steps [16][17][18][19][20][21], where advanced low-cost techniques like structure from motion and digital photogrammetric are involved in order to estimate structural complexity of large reef areas. Anyway all these advances do not take in consideration the whole process from data acquisition to output visualization.…”