The data described here result from benthic photo-quadrat surveys conducted along transects at stratified random sites (StRS), as well as climate stations and permanent sites, surveyed across the Hawaiian Archipelago during the 2019 bleaching event. Benthic habitat imagery was quantitatively analyzed using the web-based annotation tool CoralNet (Beijbom et al. 2016) with the addition of codes for bleaching of hard coral. In general, images are analyzed to produce three functional group levels of benthic cover: Tier 1 (e.g., hard coral, soft coral, macroalgae, turf algae, etc.), Tier 2 (e.g., Hard Coral = massive, branching, foliose, encrusting, etc.; Macroalgae = upright macroalgae, encrusting macroalgae, bluegreen macroalgae, and Halimeda, etc.), and Tier 3 (e.g., Hard Coral = Astreopora sp, Favia sp, Pocillopora, etc.; Macroalgae = Caulerpa sp, Dictyosphaeria sp, Padina sp, etc.). For each category of hard coral, a bleached and non-bleached option existed during analysis to facilitate the collection of coral bleaching percent cover data.

In the Main Hawaiian Islands (MHI) and some sites in the Northwestern Hawaiian Islands (NWHI), a StRS design was employed to select random sites. The survey domain encompassed the majority of the mapped area of reef and hard bottom habitats in the 0-30 m depth range. The stratification scheme included island, reef zone, and depth in all regions, as well as habitat structure type in the Main Hawaiian Islands. Sampling effort was allocated based on strata area and sites were randomly located within strata. Sites were surveyed using photo-quadrats along transects to collect benthic imagery to ultimately produce estimates of relative abundance (percent cover), frequency of occurrence, benthic community taxonomic composition and relative generic richness.

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.

Surveys conducted in the Main Hawaiian Islands were conducted during shore-based missions and were all StRS, whereas surveys in the Northwestern Hawaiian Islands were performed opportunistically during the regularly scheduled NOAA National Coral Reef Monitoring Program (NCRMP) mission and encompassed StRS as well as fixed sites, which include climate stations and permanent sites

The data from the benthic cover surveys can be accessed online via the NOAA National Centers for Environmental Information (NCEI) Ocean Archive.