Benthic surveys along a water quality gradient in Aua, American Samoa: benthic images collected during belt transect surveys in 2022

This metadata record describes the imagery collected in 2022 of Aua Reef, American Samoa by the Ecosystem Sciences Division (ESD) of NOAA, funded by the Coral Reef Conservation Program (CRCP), to study effects of land-based source pollution by establishing biological, physical, and chemical baselines.

In September 2022, NOAA scientists conducted benthic survey protocols at 18 study sites in Aua, American Samoa. The surveys implemented a one-stage stratified random sampling (StRS) design and the survey domain encompassed the majority of the mapped area of reef and hard bottom habitats in the 0 to 6 m depth range. Photoquadrat benthic images were collected along belt transect surveys of coral demography according to protocols established by NOAA National Coral Reef Monitoring Program (NCRMP) in 2015.

Thirty images were collected along one, haphazardly laid, 30-m transects. Still photographs were collected to record the benthic community composition at predetermined points along belt transect with a high-resolution digital camera mounted on a pole. Photographs were taken every 1 m from the 1 m to the 30 m mark. This work generates 30 photographs per site, which are later analyzed by ESD staff and partners using the computer program CoralNet. This analysis is the basis for estimating benthic cover and composition at each site, which is documented and archived separately.

The StRS design effectively reduces estimate variance through stratification using environmental covariates and by sampling more sites rather than more transects per site. Therefore, site-to-site comparisons should proceed with caution.