Georeferenced benthic photo quadrats and benthic cover data derived from a time series of transect surveys for Heron Reef flat and slope areas, Great Barrier Reef, 2019 - 2025

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Data Purpose: Georeferenced underwater photo quadrats were collected with the purpose of determining benthic composition for use in ecological assessment and calibration and validation of benthic habitat maps derived from remote sensing satellite or airborne imagery. Transect location, direction and depth were chosen to characterise the variation of benthic cover types on Heron Reef. The interval between photo quadrats along the transects was chosen to reflect the resolution of the satellite image data types used. Data Collection: In short, during the photo quadrat surveys, a diver or snorkeller captured photo quadrats of a set area and interval along a transect. Afterwards, photos were assigned a GPS coordinate and processed in ReefCloud (AIMS, 2024) for benthic composition. On the reef flat, snorkellers conducted these surveys at 1 – 2 m depth along a predetermined transect of ~250 – 1000 m, varying depending on heterogeneity of the area covered. On the reef slope, SCUBA divers conducted 30-minute dives along the 5 m depth contour along a predetermined ~500 – 700 m transect. The horizontal distance between photo quadrats was estimated by the surveyor counting fin kicks, and corresponded to a surface distance of ~2 – 4 m. A plumb line was used to standardise the camera distance from the benthos and maintain an image footprint of ~ 1m x 1m. The surveyor would tow a floating GPS at the surface, which was logging its position every 2 seconds. Data Processing: The coordinates of each photo quadrat were synchronised based on the timestamp of the photo quadrat and of the GPS, using specialised software (GPS-Photo by Josh Passenger: Simple tool for positioning photos along GPS tracks using linear interpolation). The coordinates of each photo quadrat were interpolated by finding the closest corresponding GPS coordinate within a set time interval (2 seconds) before and after the photo quadrat was captured. Benthic composition data was extracted using trained machine point annotations in ReefCloud (AIMS, 2024) using a labelset guide which has been provided with the benthic data. Confusion matrices were generated and are also provided alongside benthic data. Data Files Included: - Georeferenced benthic photo quadrats (2019 - 2025) - Georeferenced benthic cover data (2019 - 2025) - Confusion matrix - Labelset guide - Metadata document