Oceanographic Moorings and Intertidal Monitoring in Olympic Coast National Marine Sanctuary

Jul 8, 2025

Olympic Coast National Marine Sanctuary recently completed the first servicing mission of the 2025 season for its oceanographic mooring program. Sanctuary staff service the moorings every five weeks to swap out batteries, download data, collect water samples using an instrument that measures conductivity, temperature, and depth (CTD), and gather samples to monitor for harmful algal blooms.

Since 2000, the sanctuary has used oceanographic moorings—floating instruments anchored to the seafloor—to measure seawater conditions along approximately 135 miles of the Olympic Coast. Ten mooring sites collect data continuously from May through October, a period known as the upwelling season. During this time, deep, nutrient-rich water rises to the surface, fueling marine life—but sometimes bringing low-oxygen conditions (hypoxia) and more acidic waters that can cause stress for many species. To monitor ocean conditions in the winter months, from October to May, the sanctuary deploys simplified moorings equipped with minimal instruments to record water temperatures from the surface to the seafloor.

Instruments are mounted at different depths along each mooring, depending on the site. All moorings record water temperature, while some also measure salinity, current speed and direction, chlorophyll (an indicator of plankton productivity), and dissolved oxygen. This publicly-available data helps scientists track how ocean conditions are changing.

Olympic Coast National Marine Sanctuary staff and volunteers also recently completed their 18th year of monitoring rocky intertidal habitats—the dynamic zone where land and sea meet. This long-term monitoring is conducted in partnership with the Makah Tribe and Quinault Indian Nation on Tribal lands, along with collaborators from the Multi-Agency Rocky Intertidal Network (MARINe). Since 2008, teams have monitored two intertidal sites within sanctuary waters, while Olympic National Park monitors four additional sites within its shared jurisdiction with the sanctuary. This work provides vital information about the abundance and distribution of species, and how these communities respond to changing environmental conditions and human-caused stressors like oil spills, plastic pollution, and trampling.

At each site, scientists use plots and transects—marked by bolts permanently installed in the rocks—to collect data from the same locations each year. Some plots focus on mussels, barnacles, sea stars, or surfgrass, helping track how these species change over time. Because rocky intertidal habitats naturally experience a lot of variability, this consistent, long-term monitoring is critical for detecting broader trends. Notably, this monitoring program led to the earliest detection of sea star wasting syndrome on the U.S. West Coast in 2013. These data feed directly into the sanctuary's condition reports, which assess the health of sanctuary ecosystems and help guide management decisions.