Hyperspectral and Lidar: Complementary Tools to Identify Benthic Features and Assess the Ecological Status of Sabellaria alveolata Reefs

Bajjouk, Touria; Jauzein, Cécile; Drumetz, Lucas; Mura, Mauro Dalla; Duval, Audrey; Dubois, Stanislas F.

doi:10.3389/fmars.2020.575218

Cited by 11 publications

(10 citation statements)

References 57 publications

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“…Modern remote‐sensing technologies are advancing our ability to describe and interrogate spatial patterns in marine reef systems. In intertidal habitats like S. alveolata reef, aerial methods can capture a range of ecologically relevant information at high resolution across large extents of several km 2 (Bajjouk et al., 2020; Collin et al., 2018, 2019). The importance of 3D ecosystem structure in ecological investigations is recognized, and tools to capture and analyse 3D structure in diverse systems including subtidal reefs are becoming increasingly powerful and accessible (D’Urban Jackson et al., 2020; Lepczyk et al., 2021).…”

Section: Discussionmentioning

confidence: 99%

Three‐dimensional mapping reveals scale‐dependent dynamics in biogenic reef habitat structure

Jackson-Bué

Williams

Walker-Springett

et al. 2021

Remote Sens Ecol Conserv

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Habitat structure influences a broad range of ecological interactions and ecosystem functions across biomes. To understand and effectively manage dynamic ecosystems, we need detailed information about habitat properties and how they vary across spatial and temporal scales. Measuring and monitoring variation in three-dimensional (3D) habitat structure has traditionally been challenging, despite recognition of its importance to ecological processes. Modern 3D mapping technologies present opportunities to characterize spatial and temporal variation in habitat structure at a range of ecologically relevant scales. Biogenic reefs are structurally complex and dynamic habitats, in which structure has a pivotal influence on ecosystem biodiversity, function and resilience. For the first time, we characterized spatial and temporal dynamics in the 3D structure of intertidal Sabellaria alveolata biogenic reef across scales. We used drone-derived structure-from-motion photogrammetry and terrestrial laser scanning to characterize reef structural variation at mm-to-cm resolutions at a habitat scale (~35 000 m 2 ) over 1 year, and at a plot scale (2500 m 2 ) over 5 years (2014-2019, 6-month intervals). We found that most of the variation in reef emergence above the substrate, accretion rate and erosion rate was explained by a combination of systematic trends with shore height and positive spatial autocorrelation up to the scale of colonies (1.5 m) or small patches (up to 4 m). We identified previously undocumented temporal patterns in intertidal S. alveolata reef accretion and erosion, specifically groups of rapidly accreting, shortlived colonies and slow-accreting, long-lived colonies. We showed that these highly dynamic colony-scale structural changes compensate for each other, resulting in seemingly stable reef habitat structure over larger spatial and temporal scales. These patterns could only be detected with the use of modern 3D mapping technologies, demonstrating their potential to enhance our understanding of ecosystem dynamics across scales.

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Section: Discussionmentioning

confidence: 99%

Three‐dimensional mapping reveals scale‐dependent dynamics in biogenic reef habitat structure

Jackson-Bué

Williams

Walker-Springett

et al. 2021

Remote Sens Ecol Conserv

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“…Photo-interpretation was time-consuming, but feasible thanks to the very high image resolution. Bajjouk et al (2020) [27] similarly observed the large spectral variability of oysters colonizing S. alveolata reefs. Oysters could reach a high density in the degraded parts of the reef with variable orientations of the shells, from horizontal to vertical [26], sometimes covered by sand (Figures 5C and 7(C1,C2)).…”

Section: Epibiont Mappingmentioning

confidence: 92%

“…The reef footprint was mapped considering a gradient encompassing the largest reef structures, but also smaller clusters of coalescent structures, and finally the smallest isolated clumps (Figure 4). The latter could not be identified with a 50-cm image resolution from optical airborne data [27]. Hummocks and small coalescent structures were abundant in transition zones between the main reefs in the southern and eastern parts of the study area (Figure 4).…”

Section: Identification Of the Reef Footprintmentioning

confidence: 98%

“…The Phantom 4 Multispectral UAV has only five bands. This problem can now be overcome with a higher hyperspectral resolution, as demonstrated by Bajjouk et al (2020) [27], but this is not very accessible and is a costly technology. In the healthy parts of the reef, the tubes are built up with resuspended sand grains and have a similar color to the surrounding sediment [1].…”

Section: Identification Of the Reef Footprintmentioning

confidence: 99%

“…Yet, they have rarely been used to map intertidal reef habitats [25], as the resolution is often too coarse to describe sub-meter reef features or simply because satellite overpass does not coincide with the lowest tides. Airborne campaigns with multi-or hyper-spectral sensors and topographic/bathymetric LiDAR, as well as underwater sounder dedicated to shallow water, can overcome these tidal restrictions and provide relevant high spatial and spectral resolutions for biogenic reef mapping [22,[26][27][28][29]. However, the costs of instrumentation and deployment may limit their use by public environmental agencies.…”

Section: Introductionmentioning

confidence: 99%

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Topographic Analysis of Intertidal Polychaete Reefs (Sabellaria alveolata) at a Very High Spatial Resolution

Brunier

Oiry

Gruet³

et al. 2022

Remote Sensing

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In temperate coastal regions of Western Europe, the polychaete Sabellaria alveolata (Linné) builds large intertidal reefs of several hectares on soft-bottom substrates. These reefs are protected by the European Habitat Directive EEC/92/43 under the status of biogenic structures hosting a high biodiversity and providing ecological functions such as protection against coastal erosion. As an alternative to time-consuming field campaigns, a UAV-based Structure-from-Motion photogrammetric survey was carried out in October 2020 over Noirmoutier Island (France) where the second-largest known European reef is located in a tidal delta. A DJI Phantom 4 Multispectral UAV provided a topographic dataset at very high resolutions of 5 cm/pixel for the Digital Surface Model (DSM) and 2.63 cm/pixel for the multispectral orthomosaic images. The reef footprint was mapped using a combination of two topographic indices: the Topographic Openness Index and the Topographic Position Index. The reef structures covered an area of 8.15 ha, with 89% corresponding to the main reef composed of connected and continuous biogenic structures, 7.6% of large isolated structures (<60 m2), and 4.4% of small isolated reef clumps (<2 m2). To further describe the topographic complexity of the reef, the Geomorphon landform classification was used. The spatial distribution of tabular platforms considered as a healthy stage of the reef in contrast to a degraded stage was mapped with a proxy that consists in comparing the reef volume to a theoretical tabular-shaped reef volume. Epibionts colonizing the reef (macroalgae, mussels, and oysters) were also mapped by combining multispectral indices such as the Normalised Difference Vegetation Index and simple band ratios with topographic indices. A confusion matrix showed that macroalgae and mussels were satisfactorily identified but that oysters could not be detected by an automated procedure due to their spectral complexity. The topographic indices used in this work should now be further exploited to propose a health index for these large intertidal reefs.

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Benthic habitat mapping: A review of three decades of mapping biological patterns on the seafloor

Misiuk,

Brown

2024

Estuarine, Coastal and Shelf Science

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Hyperspectral and Lidar: Complementary Tools to Identify Benthic Features and Assess the Ecological Status of Sabellaria alveolata Reefs

Cited by 11 publications

References 57 publications

Three‐dimensional mapping reveals scale‐dependent dynamics in biogenic reef habitat structure

Three‐dimensional mapping reveals scale‐dependent dynamics in biogenic reef habitat structure

Topographic Analysis of Intertidal Polychaete Reefs (Sabellaria alveolata) at a Very High Spatial Resolution

Benthic habitat mapping: A review of three decades of mapping biological patterns on the seafloor

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