Benthic Surveys in Vatia, American Samoa: benthic cover derived from analysis of benthic images collected during belt transect surveys of coral demography in 2015 and 2020

Jurisdictional managers have expressed concerns that nutrients from the village of Vatia, Tutuila, American Samoa, are having an adverse effect on the adjacent coral reef ecosystem. Excess nutrient loads promote increases in algal growth that can have deleterious effects on corals, such as benthic algae outcompeting and overgrowing corals. Nitrogen and phosphorus can also directly impact corals by lowering fertilization success, and reducing both photosynthesis and calcification rates. Land-based contributions of nutrients come from a variety of sources; in Vatia the most likely sources are poor wastewater management from piggeries and septic systems.

NOAA scientists conducted benthic surveys to establish a baseline against which to compare changes in the algal and coral assemblages in response to nutrient fluxes.

The benthic cover data described here were generated from the quantitative analysis of photoquadrat benthic images using image analysis software, whereby random points are projected on each image and the benthic elements falling directly underneath each point are identified. The images were collected at 18 and 24 stratified randomly selected sites in 2015 and 2020 respectively, during belt transect surveys of coral demography by the NOAA Ecosystem Sciences Division (ESD; former Coral Reef Ecosystem Program CREP). Five of the 18 sites surveyed in 2015 were resurveyed periodically in 2016 (January, March, June, September, and December) to assess any short-term temporal changes in the benthic composition.

The benthic cover data can be accessed online via the NOAA National Centers for Environmental Information (NCEI) Ocean Archive. The benthic images and coral demography data are described and archived separately.