Structure-from-motion photogrammetry demonstrates variability in coral growth within colonies and across habitats

Abstract

Coral growth is an important metric of coral health and underpins reef-scale functional attributes such as structural complexity and calcium carbonate production. There persists, however, a paucity of growth data for most reef-building regions, especially for coral species whose skeletal architecture prevents the use of traditional methods such as coring and Alizarin staining. We used structure-from-motion photogrammetry to quantify a range of colony-scale growth metrics for six coral species in the Mexican Caribbean and present a newly developed workflow to measure colony volume change over time. Our results provide the first growth metrics for two species that are now major space occupiers on Caribbean reefs, Agaricia agaricites and Agaricia tenuifolia. We also document higher linear extension, volume increase and calcification rates within back reef compared to fore reef environments for four other common species: Orbicella faveolata, Porites astreoides, Siderastrea siderea and Pseudodiploria strigosa. Linear extension rates in our study were lower than those obtained via computed tomography (CT) scans of coral cores from the same sites, as the photogrammetry method averages growth in all dimensions, while the CT method depicts growth only along the main growth axis (upwards). The comparison of direct volume change versus potential volume increase calculated from linear extension emphasizes the importance of assessing whole colony growth to improve calcification estimates. The method presented here provides an approach that can generate accurate calcification estimates alongside a range of other whole-colony growth metrics in a non-invasive way.

Remote sensing of Antarctic polychaete reefs (Serpula narconensis): reproducible workflows for quantifying benthic structural complexity with action cameras, remotely operated vehicles and structure‐from‐motion photogrammetry

“…Multiple limitations emerge due to the lack of true depths and geo‐referenced imagery, such as repeated measurements for long‐term monitoring (Lange et al., 2022; Pascoe et al., 2021). Therefore, development of accurate navigation systems, laser scaling and ground control points that can be easily deployed and retrieved with ROVs is essential to increase accuracy and ensure that changes are detected.…”

“…This approach is limited to short photo-transect lengths (1-7 m), with high frontal image overlap (>90%), stable image acquisition platforms, laser scalers, standardized post-processing protocols and considerable time for ensuring spatially coherent models are obtained. Multiple limitations emerge due to the lack of true depths and geo-referenced imagery, such as repeated measurements for long-term monitoring (Lange et al, 2022;Pascoe et al, 2021). Therefore, development of accurate navigation systems, laser scaling and ground control points that can be easily deployed and retrieved with ROVs is essential to increase accuracy and ensure that changes are detected.…”

“…Applications of SfM has shown great potential for providing novel insights into seascape ecology, as demonstrated by extensive research on structural metrics (Bongaerts et al., 2021; Lazarus & Belmaker, 2021; Lepczyk et al., 2021; Urbina‐Barreto et al., 2022). Successful protocols have been developed for acquiring structural complexity metrics (e.g., surface complexity, slope, curvatures and fractal dimension) via SfM (Table 1) at multiple spatial scales (several m 2 and between sites) (Bayley & Mogg, 2020; Fukunaga et al., 2019; Lange et al., 2022; Lange & Perry, 2020; Lechene et al., 2019; Young et al., 2017). These protocols rely on the placement of auxiliary reference objects of known dimensions, such as ground control point units (Fukunaga, Burns, et al., 2020) and geodesical networks (Nocerino et al., 2020), permitting the integration of structural metrics in long‐term observations of benthic communities, such as coral growth (Lange et al., 2022; Rossi et al., 2019), effects of natural disturbances (Pascoe et al., 2021), and describe fish functional diversity (Fukunaga, Burns, et al., 2020; Urbina‐Barreto et al., 2022).…”

“…Successful protocols have been developed for acquiring structural complexity metrics (e.g., surface complexity, slope, curvatures and fractal dimension) via SfM (Table 1) at multiple spatial scales (several m 2 and between sites) (Bayley & Mogg, 2020; Fukunaga et al., 2019; Lange et al., 2022; Lange & Perry, 2020; Lechene et al., 2019; Young et al., 2017). These protocols rely on the placement of auxiliary reference objects of known dimensions, such as ground control point units (Fukunaga, Burns, et al., 2020) and geodesical networks (Nocerino et al., 2020), permitting the integration of structural metrics in long‐term observations of benthic communities, such as coral growth (Lange et al., 2022; Rossi et al., 2019), effects of natural disturbances (Pascoe et al., 2021), and describe fish functional diversity (Fukunaga, Burns, et al., 2020; Urbina‐Barreto et al., 2022). SfM has been successfully applied via human‐diver surveys of Antarctic coastal benthic ecosystems which have also identified the possible applications in long‐term monitoring campaigns (Menna et al., 2022; Piazza et al., 2018, 2019); however, these studies did not address structural complexity.…”

Structural Complexity of Coral Reefs in Guam, Mariana Islands

“…SfM is a rapid, cost-effective technique that has the potential to alleviate the aforementioned issues associated with traditional survey methods [42,48,49]. SfM has been shown to effectively quantify structure at scales ranging from individual coral colonies to entire reef sites [36,45,50,51]. It has also been used to quantify the influence of structural complexity on fish communities, the rate of coral growth and reef accretion, the effect of coral colony morphology on structural complexity, and changes in structural complexity following disturbance events [39,42,[51][52][53][54].…”