Structure-from-Motion Coral Demography derived from Stratified Random Site Imagery collected across the Mariana Archipelago from 2022-05-10 to 2022-06-01 for methods comparison (NCEI Accession 0280938)

Coral adult and juvenile coral colony demographic data described in this dataset are derived from the GIS analysis of benthic photomosaic imagery collected across the Mariana Archipelago in 2022 for a methods comparison with in situ diver data. Official National Coral Reef Monitoring Program (NCRMP) coral demographic data is archived separately under NCEI Accession 0298217. The source imagery was collected using a Structure from Motion (SfM) approach during in-water surveys conducted by divers. Data was collected during the NOAA Pacific Islands Fisheries Science Center (PIFSC) and Ecosystem Sciences Division (ESD) led NCRMP mission across the Mariana Archipelago from 2022-05-10 to 2022-06-01.

The SfM surveys are part of the Rapid Ecological Assessment (REA) surveys for corals and fish conducted during ESD-led NCRMP missions. Surveys were conducted at sites randomly stratified across sub-island sectors and three depth strata (shallow: 0-6m, mid: 6-18m and deep: >18m). These sites represent a broad range of depths (1-25 m), habitat types (aggregate reef, patch reef, pavement, rock and boulder and rubble), coral cover, and diving conditions. Allocation of sampling effort was proportional to strata area and variance in coral density. The StRS design effectively reduces estimate variance through stratification using environmental covariates and by sampling more sites rather than sampling more transects at a site. Therefore, site-level estimates and site to site comparisons should be used with caution.

During each survey, an 18m transect line was deployed along the isobath and photographed using underwater cameras while swimming in a back and forth swim pattern for later processing using an SfM approach. At depths of 1-20 m, SfM surveys were conducted over a 3 x 20m area and at depths > 20m, a 3 x 13m area was surveyed, both with the transect running down the middle of the survey area. The photographs were processed using Agisoft Metashape software to generate orthomosaic images that were analyzed in ArcGIS for juvenile and adult coral colony demographic metrics. Data was collected for each site within four 2.5m2 segments, each 1m wide, along the transect (at 0-2.5m, 5-7.5m, 10-12.5m, and 15-17.5m). At deeper sites where a 3 x 13m area was surveyed, only the first three segments were analyzed in ArcGIS. For each adult coral colony (> 5cm in diameter), maximum diameter, ID (to lowest taxonomic level), and estimated percent old mortality were recorded. Bleaching extent (% of living tissue with reduced pigmentation) and severity were also recorded. Juvenile coral colonies (0.7 to 5cm maximum diameter) were recorded within the first 1 m2 of the first 3 segments. For juvenile colonies, only ID and maximum diameter were recorded.