The data in this package include benthic percent cover data collected at High Priority Reef Areas by the Guam Long-term Coral Reef Monitoring Program (GLTMP). These data were generated through the analysis of images obtained by benthic photo transect surveys at numerous sampling stations (= one transect) within the boundaries of each HPRA. Benthic cover estimates were initially derived from photo transect images using Coral Point Count with Excel extensions (CPCe; Kohler and Gill 2006) point sampling software, but the web-based image analysis platform CoralNet (Beijborn et al. 2012, Beijborn 2015) was used beginning with the 2019 images.

These data were collected using a split-panel sampling approach, whereby a mix of permanent and non-permanent sampling stations (one sampling station = one transect) are visited within each HPRA. The HPRAs were selected by an advisory body comprised of reef managers, researchers, and technicians. The sites were not selected randomly from around the island and thus should not be considered representative of reef condition at the island-scale. While the general ___location of the HPRAs were selected based on management priority, the site boundaries were delineated using bathymetry and benthic habitat data within ArcGIS; the locations of the sampling stations were generated randomly within each site’s boundaries using ArcGIS.

The benthic photo transect surveys, as well as reef fish SPC, macroinvertebrate belt transect, and rugosity surveys are carried out on an annual basis along the seaward slope between 7 and 15 m depth in the Tumon Bay Marine Preserve and in East Agana Bay, while surveys are carried out biennially within the Piti Bomb Holes Marine Preserve, the Achang Reef Flat Marine Preserve, the eastern side of the Cocos Barrier Reef (Cocos-East), and Fouha Bay. Surveys were also carried at along reef margin (1-2 m) and slope (2-15 m) of Western Shoals, in Apra Harbor, in 2011. The GLTMP has conducted surveys at the Tumon and East Agana HPRAs since 2010 and the Piti HPRA since 2012. Data collection for the Achang and Cocos-East HPRAs began in 2014 and at the Fouha Bay HPRA in 2015. Baseline data is available for the Western Shoals HPRA from 2011 but this site has not been revisited since its establishment due to shifting management priorities.

Newly generated annotations are acquired from CoralNet and integrated with a master benthic cover data set using a custom R script. These data do not contain zero counts for benthic classes not observed at a given sampling station, but zero counts should be accounted for when calculating mean values for parameters across sampling stations (e.g., by using the expand_grid function in R). Note that while the SURVEY_YEAR value is generally consistent with the SURVEY_DATE, the SURVEY_YEAR value for several sampling stations in the Piti HPRA is not consistent with the SURVEY_DATE. These stations were surveyed in November and December of 2017, but surveys at the remainder of the sampling stations were completed between March and August of 2018. The SURVEY_YEAR was changed to 2018 for the stations surveyed in late 2017 in order to allow these stations to be considered together in a time series analysis.