2025 Coral Reef Survey Sets New Records in the Mariana Archipelago

Scientists have returned from a 3-month expedition assessing coral reef health and ocean conditions in Wake Atoll, Guam, and the Commonwealth of the Northern Mariana Islands. The effort was part of the National Coral Reef Monitoring Program . The mission, funded by the Coral Reef Conservation Program , broke previous records for the number of fish and benthic surveys completed in a single year for this region.

Each year, scientists from NOAA's Pacific Islands Fisheries Science Center spend several months at sea gathering long-term data to monitor changes in coral reef ecosystems. These data help scientists, resource managers, and communities conserve reefs that protect our coastlines, sustain fisheries, and power local economies.

This year's mission took scientists, aboard NOAA ship Oscar Elton Sette , to the coral reefs of the Mariana Archipelago and Wake Atoll. Since the early 2000s, NOAA Fisheries has surveyed this region regularly, and the data collected this year will further enhance the long-term dataset. Summarized results from recent years are available through NOAA's Data Visualization Tool , and all data can be accessed via Data.gov by searching "National Coral Reef Monitoring Program."

Survey Study Area

Scientists traveled more than 3,500 kilometers (2,175 miles) from Honolulu, Hawai'i to Wake Atoll. That's roughly the same distance as crossing the continental United States from coast to coast! During the 10-day journey aboard Oscar Elton Sette , they prepared gear and instruments for the upcoming coral reef surveys.

Following 6 days of surveys around Wake Atoll, the ship traveled another 6 days to reach Guam. Over the next 2 months, scientists completed surveys throughout the Mariana Archipelago. They collected data critical to understanding the health and resilience of coral reefs in the region.

Islands visited in the Mariana archipelago:

• Uracas (also known as Farallon de Pájaros)
• Maug
• Agrihan
• Pagan
• Alamagan
• Guguan
• Sarigan
• Saipan
• Tinian
• Aguijan
• Rota
• Guam

Survey Highlights

To build a comprehensive picture of coral reef health, scientists used multiple teams and techniques to study reef fish, coral, and ocean chemistry.

Fish Surveys

A fish survey team recorded detailed observations of fish, including their species, numbers, and sizes. Working in pairs, divers used scuba equipment to record fish at specific reef locations, repeating the process at multiple sites around each island.

This year, the team completed 422 fish surveys across Wake Atoll, Guam, and the Commonwealth of the Northern Mariana Islands. This is the highest number ever conducted in a single year for this region, surpassing the previous record from 2014 by 89 surveys.

At Wake Atoll, scientists also performed towboard surveys, in which divers are pulled behind a small boat. This approach helps spot more mobile and rare fish species. Scientists surveyed the entire atoll looking for the humphead wrasse, bumphead parrotfish, and scalloped hammerhead shark. Unfortunately, they saw very few of these fish.

Ocean Chemistry and Acidification Research

Simultaneous with fish surveys, another team collected ocean condition and chemistry data at established sites that have been surveyed since as early as 2000. One of the noteworthy sites is at Maug Caldera, where underwater volcanic vents release carbon dioxide. This lowers the pH of seawater near the vents, creating an acidic environment and a perfect stage to study the effects of ocean acidification on coral reefs.

This year the team successfully continued the long-term study that began in 2003. Coral cover and diversity of nearby coral communities have been significantly reduced by ocean acidification over the past 22 years of routine surveys, although these effects are localized.

Coral Structure Imaging

Using high-resolution cameras, scientists captured thousands of reef images to study coral. These images are stitched together forming a photomosaic, or 3D model, which helps to determine if coral cover is increasing or decreasing, how fast corals are growing, and how that may be related to ocean conditions. Scientists can even track individual coral colonies over time to see how they change. Photos were collected at 330 sites during this mission, setting another record!

Plankton and Larval Fish Sampling

While divers slept after long days monitoring coral reefs, the ship headed offshore so another team could collect plankton samples in search of fish larvae. Scientists towed a large net through the dark waters, capturing tiny, drifting organisms that were later examined under a microscope. By studying fish at this early life stage, scientists gain insight into where and when fish are spawning. They also learn about the overall health of fish populations in the region. Each small sample provides a microscopic glimpse into the early lives of marine species in the Mariana Archipelago.

What's Next

Now back in Honolulu, scientists will spend the next year reviewing the data for accuracy and generating reports to assist management of Pacific reefs. We will make the data publicly available once their review is finished.

The record number of surveys completed this year improves regional data. It also reflects the ability of the team to maximize data collection with limited time. By using new technology to analyze coral images after returning from the field, they had more time to focus on fish surveys and capture more coral images.

In 2026, the team plans to survey American Sāmoa, Howland, Baker, and Jarvis Islands, as well as Palmyra Atoll and Kingman Reef. These datasets also continue decades-long coral reef monitoring efforts that provide data to better manage Pacific coral reefs. Through tourism, fishing, and recreation, these reefs generate a $3.4 billion dollar value to the U.S. economy.

Through persistent monitoring, science-based collaboration, and local partnerships, NOAA's long-term reef surveys help safeguard coral ecosystems for future generations.

USFWS Special Use Permit (Ritidian Point) #12518-25006
NPS Scientific Research and Collecting Permit #WAPA-2025-SCI-0003
CNMI DLNR DFW Scientific Research License # SRC25-10-RE
Guam DAWR Research Permit #SCR-MPA-25-008