Comparison of Standard Caribbean Coral Reef Monitoring Protocols and Underwater Digital Photogrammetry to Characterize Hard Coral Species Composition, Abundance and Cover

Abstract

The precise assessing and monitoring of coral reefs are necessary to address and understand the threats and changes in coral communities. With the development of new technologies and algorithms for image processing, new protocols like underwater photogrammetry are implemented to study these ecosystems. This study compares the main ecological metrics for reef condition assessment, obtained with an underwater digital photogrammetry protocol (UWP) and traditional sampling design simulations in coral reefs of the Cozumel Reefs National Park. Three orthomosaics (380 m2) per reef on six fringing reefs were constructed, and the hard coral community characterized using a Geographic Information System (GIS). The orthomosaics were also used as a basis to simulate transect lines and obtain data on the hard coral community according to the video transect (VT) protocol, point intercept (PIT) protocol, and the Atlantic and Gulf Rapid Reef Assessment (AGRRA) protocol. Higher colony abundance, species richness, and lower coral cover estimates (p < 0.05) were obtained with the UWP. This protocol was also sensitive to small sized species. All the sampling designs showed similar capability to identify dominant species in terms of colony abundance and coral cover. The VT, PIT, and AGGRA showed similar coral cover values (p > 0.05), which seems to indicate that these sampling designs overestimate this important metric. Our results will help to understand and integrate the observations obtained with UWP with long-term data obtained with commonly used monitoring protocols in the Caribbean region.

Diver-generated photomosaics as a tool for monitoring temperate rocky reef ecosystems

“…In this study we compared commonly used ecosystem monitoring metrics on temperate rocky reefs dominated by urchin barrens between data extracted from high-resolution, SfM derived, photomosaics and traditional diver-based field quadrats. Primary survey metrics, including sea urchin densities, kelp canopy cover and benthic community composition data, were similar between the two methodologies, consistent with other papers comparing benthic data collected by photography with traditional methods (Dodge et al, 1982;Preskitt et al, 2004;Parravicini et al, 2009;Jokiel et al, 2015) and more specifically comparing the use of photomosaics with traditional methods (Ling, et al, 2016;Raoult et al, 2016;Burns et al, 2020;Barrera-Falcon et al, 2021;Couch et al, 2021).…”

Rebuilding Coral Reefs: How tourism can be a driver behind solutions in a changing ocean

“…These contradictory results suggest that the difference is directly related to the sampling method used. It seems that there is an overestimation of the data when using traditional methods, in this case AGRRA as reported by Barrera-Falcon et al 2021 [42].…”

Coral Reef Benthos Classification Using Data from a Short-Range Multispectral Sensor

“…Plot A was surveyed at ~1.8 m from the bottom using natural light, under the assumption that the downwelling light sensor (DLS) from the camera would compensate for the light variability during the imagery survey; this plot had large coral colonies, octocorals, and encompassed a deeper section in a sand channel between two spurs. The distance was selected following similar digital photogrammetry approaches [12,14,15,44].…”

“…This optimal distance to the substrate of 0.5 m to collect useful data on at least four bands (B, G, R, RE) increases the time needed to survey that area as sweeps are narrower and data require very slow swimming to avoid image blurring. In comparison, other underwater digital photogrammetry approaches acquire pictures at distances ranging from 1 to 2 m above the bottom using camera lenses with similar or wider FOV (47.2 • for RedEdge-M vs. 42 • to 100 • for 55 to 18 mm lenses) [12,14,15,44], allowing the photographic survey of plots up to 100 m 2 in roughly the same time.…”

“…In the last two decades, the implementation and advancement of the use of digital underwater photogrammetric techniques [3][4][5][6][7] coupled with the general availability of structure from motion software (SfM, i.e., Agisoft's Metashape Pro, Pix4D), has led to strong research lines on a wide range of applications, from coral colonies characterization to applications for reef benthos assessment and ecological hypothesis testing [8][9][10][11][12][13][14][15][16], taking in-situ imagery records to a new analytic level, supported by the accurate re-creation of benthic features in ultra-high spatial resolution and combined with 3D perspectives.…”