Comparison of two photographic methodologies for collecting and analyzing the condition of coral reef ecosystems

Abstract

Abstract. Coral reefs are declining rapidly in response to unprecedented rates of environmental change.Rapid and scalable measurements of how benthic ecosystems are responding to these changes are critically important. Recent technological developments associated with the XL Catlin Seaview Survey have begun to provide high-resolution 1-m 2 photographic quadrats of~1.8-2 km of coral reefs at 10 m depth by using a semi-autonomous image collection SeaView II camera system (SVII). The rapid collection of images by SVII can result in images being taken at a variable distance (1-2 m) from the substrate as well as having natural light variability between images captured. This variability can affect the quality of taxonomic resolution archived from photographic quadrats captured by SVII. Conventional approaches for taking photographic quadrats of coral reefs involve taking images from a fixed distance with the use of artificial light. These methods often provide images that enable high taxonomic resolution, but are typically used to cover areas of 50-150 m. Here, we select key metrics associated with coral reef condition from a functional perspective to contrast how much is lost in terms of association and agreement from image annotations using SVII images (1-m 2 photoquadrats) compared to conventional methods, capturing 0.5-m 2 photoquadrats using a digital single lens reflex camera from a fixed height of 0.5 m above the benthos. Comparisons were made over the same 50-m linear transects at 15 sites in the Maldives. Photoquadrats were manually analyzed using an online image annotation tool and image repository called coral net with 25 randomly placed dots per 0.5 m 2 of a quadrat. Our results reveal high levels of correlation and agreement between methods when measuring the abundance of hard corals as a functional group and individual labels, which make up hard corals as a functional group. These results demonstrate the two methods are comparable when measuring functional groups and coral communities on coral reefs. Therefore, involving rapid semi-automated technologies that maximize data collection for monitoring coral reefs does not necessarily imply that taxonomic resolution is compromised. This insight has important ramifications for detecting important changes in coral reef condition, such as a decline in coral cover or shifts in benthic community composition.

Coral Reef Community Changes in Karimunjawa National Park, Indonesia: Assessing the Efficacy of Management in the Face of Local and Global Stressors

“…Different survey methodologies may explain why our finding of~27% Hard coral cover in 2014 was lower than observations of~38-60% reported in 2009 [55] and 62% (range 34-97%) reported in 2015 [56]. Traditional 50 m survey line intercepts often target locations dominated by corals, while the 750 m+ transects conducted as part of this study would have transited more diverse habitats, including sand filled gullies and rubble patches avoided by standard 50 m transects [57]. This also explains negative correlations identified between Algae-Sediment, and Hard coral-Sediment that were related to zone ( Figure 5): some transects transited more areas of sand, where Algae and Hard coral which need hard substrate to attach to, cannot grow.…”

Marine heatwaves modulate the genotypic and physiological responses of reef‐building corals to subsequent heat stress

“…Before the heatwave (November/December 2019), benthic community composition was determined along 8 × 30 m transects per site using the modified methodology of Bryant et al. ( 2017 ) (Table S1 , for full details see Appendix S1 ). In order to assess isotope end members of planktonic food sources, plankton tows were conducted and seawater was collected and filtered (0.7 μm nominal pore size; Whatman GF/F) for particulate organic matter (POM) at each site (for full details see Appendix S1 ).…”

“…During the thermal anomalies preceding this study (2016 and 2017), Lizard Island on the northern GBR experienced severe thermal stress, while Heron Island on the southern GBR experienced minimal stress (Figure 1) (Hughes et al, 2017). Before the heatwave (November/December 2019), benthic community composition was determined along 8 × 30 m transects per site using the modified methodology of Bryant et al (2017) (Table S1, for full details see Appendix S1). In order to assess isotope end members of planktonic food sources, plankton tows were conducted and seawater was collected and filtered (0.7 μm nominal pore size; Whatman GF/F) for particulate organic matter (POM) at each site (for full details see Appendix S1).…”

Integrated approach to analyse benthic images from an autonomous underwater vehicle deployed at Pemba Island, Tanzania

“…Coral reefs are undergoing dramatic changes and shifts in their community structure, indicating the necessity to monitor these changes rapidly and on a large scale (Bryant et al, 2017). Until now, human observers have been the major source of information on coral reefs.…”