The National Coral Reef Monitoring Program (NCRMP) successfully completed all scientific operations on the first leg of the 2026 mission in American Samoa and Pacific Islands Heritage Marine National Monument (PIHMNM) aboard NOAA Ship Oscar Elton Sette. The team concluded surveys in Palmyra Atoll, Kingman Reef, and Jarvis Island. Also sampled were other ocean conditions, reef health, fish populations and eDNA.
By the numbers: what did NCRMP survey?
- 141 Stationary Point Count (SPC) fish surveys
- 182 Benthic surveys
- 129 Structure-from-Motion (SfM) 3D reef images (121 belts, 8 spirals)
- 103 CTD casts/water samples
- 54 Midwater trawl tows
- 37 Subsurface Temperature Recorders (STRs) deployed,
- 25 STRs recovered
- 25 Calcification Accretion Units (CAUs) deployed: how much carbonate accretion
- 35 CAUs recovered
- 15 Bioerosion Monitoring Units (BMUs) deployed: how much carbonate eroded
- 9 BMUs recorvered
- 6 Carbonate budget surveys: are reefs growing or eroding
- 1 diel suite deployment
- 58 eDNA samples
- 66 genetic voucher specimens
Dive in with NCRMP’s 2026 interactive map.
How does NCRMP 2026 assess the effects of ocean acidification on coral reefs?
As part of NCRMP’s comprehensive surveys, they monitor ocean acidification and assessing how it might affect reef accretion, or growth. Corals grow their skeletons using the mineral building block aragonite, which is a dense form of carbonate. Monitoring the chemistry of surrounding waters will determine how saturated this mineral is, which can affect how much energy a coral uses to build and maintain their structure.
A good long-term way of measuring the effects of ocean acidification and how much a coral reef is accreting is through special plates called calcification accretion units (CAUs). Conversely, Bioerosion Monitoring Units (BMUs) measure how much parrotfish, urchins and other marine life break down the carbonate. Researchers embed these CAUs remain in the reefs and leave them until they return a year or more later. The amount of aragonite is measured to determine if the reef has had net growth or erosion.
The carbonate budget – balancing a coral reef’s checkbook
The carbonate budget tells us if a coral reef is getting bigger or smaller. It is similar to your bank account. Where the production or growth of of the reef measured by CAUs and benthic surveys like our deposits. Bioerosion by marine life is like our withdrawals. If there is more withdrawaks then deposits, your net balance will get smaller. Ocean acidification is like a tax that makes it harder to deposit.
In addition to using CAUs and BMUs, scientists measure the carbonate budget by combining benthic surveys, bioeroder counts, and 3D imaging to calculate net growth or erosion. Benthic surveys are conducted by divers to record the species, size, and structural complexity of calcifiers like corals and crustose coralline algae in the reef. Along the same transects, they count bioeroders. Finally, they take high resolution 3D images to reconstruct the entire reef back on shore. The budget is determined from how much carbonate is produced compared to how much is eroded.
This combination of monitoring ocean chemistry and measuring aragonite has been an effective way to determine how ocean acidification can drive coral reef health. Researchers used more than a decade of NCMRP data from missions like the current one in American Samoa and PIHMNM to determine how ocean acidification factors in.
Pretty in Pink: Muliava (Rose Atoll) reefs are pink from the crustose coralline algae, another calcifying organism. Calcifyers like corals and these algae are sensitive to ocean acidification.
Check out this visual story about why places like Muliava, also known as Rose Atoll, have robust coral reefs compared to other places abased on research from missions like this one.
The survey continues as part of a long-term monitoring effort
Leg two is now underway with the entire mission set to conclude July 30. By consistently and regularly surveying our Pacific Island coral reefs, we can monitor and track how ocean change affects coral reefs – an important part of managing and conserving these ecosystems, fisheries and economies. American Samoa was last surveyed in 2023, and this will be the tenth visit since 2002. The NOAA Ocean Acidification Program funds the monitoring and assessment of ocean acidification on NCRMP missions.
