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Padilla Bay National Estuarine Research Reserve:
A Reserve for Eelgrass

Located approximately 100 km north of ERF’s conference site in Seattle, the Padilla Bay National Estuarine Research Reserve (NERR) offers some protection for one of the largest contiguous eelgrass beds on the west coast of North America. The Reserve consists of more than 3,000 hectares of intertidal
flats; subtidal eelgrasses cover an additional 250 hectares of subtidal slopes and channels. Set aside for
research, education, and public information, Padilla Bay NERR has supported and encouraged
research in the bay to better understand the role of eelgrass communities in Pacific Northwest
ecosystems, invasive species, and agriculture-estuary interactions.

The Padilla Bay Reserve has developed a collaborative relationship with Western Washington Uni-versity’s
Shannon Point Marine Center located in Anacortes, just west of Padilla Bay, as well as with the University of Washington. Padilla Bay NERR awards Research Assistantships in Estuarine Science and Coastal Zone Management each year to selected students who conduct their thesis research in Padilla Bay; NOAA funds
two graduate students each year through the NERR System Graduate Research Fellowship Program.

Eelgrass Ecosystems
Research by these students and other scientists have indicated the importance of eelgrasses and eelgrass communities in Padilla Bay. These studies have also indicated the importance of eelgrass communities in the life cycle of a variety of estuarine fauna of the Pacific Northwest. Out migrating juvenile salmon spend varying lengths of time in estuaries and eelgrass beds before moving to the North Pacific. Chinook and Chum salmon, in particular, are found in Padilla Bay eelgrass beds. Charles Simenstad (ERF 2003 Program Co-Chair) and others, discovered that the most important food item for Chum salmon in Padilla Bay was harpacticoid copepods, which are part of the epiphyte community on eelgrass leaves.

Another important Pacific Northwest species, Dungeness crab (Cancer magister) is abundant in Padilla Bay. Juveniles of C. magister settle in Padilla Bay, apparently from both Puget Sound and oceanic sources, with early instars found primarily in intertidal eelgrass and Ulva habitat. The eelgrass habitat provides protection, substrate, and food for the early instars. After one year, the juveniles prefer another Padilla Bay habitat: shallow channels and subtidal eelgrass.

Waterfowl have been and continue to be an important component of the Padilla Bay food web. Widgeon, pintail, mallard, green-winged teal, and scoters are particularly abundant during autumn and spring migrations, as well as a large number that over winter in the bay. The herbivorous brant, Branta bernicla, feed directly on the eelgrasses, with some evidence that most of one race, the High Arctic Brant, over winter in Padilla Bay rather than in Mexico as do most other brant. The proximity of the agricultural lands in the Padilla Bay watershed may also be an important reason for Padilla Bay to be a favored wintering
area for so many waterfowl.

Rural Development and Suburban Sprawl
Although the watershed of Padilla Bay is primarily in agricultural land use, rural development and suburban sprawl are increasing threats. In a different research emphasis, the Padilla Bay NERR purchased a farm on the shores of Padilla Bay and, with the local farming community, investigated various farming practices that could lessen the water quality impact of annual crop farming on the estuary. (Time-tested farming practices,
like a well-established winter cover crop, also seemed to be best practices for the estuary.)

Exotic Invaders
Control, monitoring, and research on non-native species has been part of the protection plan for Padilla Bay for long-term research and education. One of the controversial non-natives has been Spartina alterniflora.

After considerable discussion and advice from Pacific Northwest estuarine scientists, Padilla Bay NERR began a control program that has eliminated most of the S. alterniflora from the bay. However, Spartina anglica seedlings appear each year from infestations in surrounding bays and require annual monitoring and control. In contrast, another non-native plant, Zostera japonica, has become well established in the bay and has received a certain level of protection from Washington state agencies.

A non-native species that has been moving north up the west coast is the European Green Crab, Carcinus maenus. Padilla Bay has joined several other National Estuarine Research Reserves, including South Slough in Oregon and Elkhorn Slough in California in a pilot invasive crab monitoring project. Replicate trays with
appropriate habitat for crabs are set out and collected every three months, and sizes and numbers of
native and non-native crabs determined. The project is still in progress, but the European Green Crab
has not reached Padilla Bay yet although it has been found in Elkhorn Slough and South Slough.

Evolution of an Estuary
Although designated a National Estuarine Research Reserve in 1980, Padilla Bay has been cut off as an estuary from the Skagit and Samish Rivers that used to flow to Padilla Bay via a system of distributary
channels until the area was “reclaimed” in the 1880s. Now the fresh water in the polyhaline Padilla Bay estuary comes from distant rivers flowing into Puget Sound and the Strait of Georgia; the shores of the bay are either dikes or bluffs of raised marine terraces left by the last glacial retreat of about 10,000 years ago.
Intertidal flats cover about 75% of the surface area of the bay with the other 25% a system of den-dritic
channels that distribute and drain the 2.5m semi-diurnal tides. Hat Island, on the western edge of Padilla Bay straddles the contrasting topographywith eelgrass covered intertidal flats on one side and a drop-off to 100 m on the other side.

More information about Padilla Bay NationalEstuarine Research Reserve can be found online at
www.inlet.geol.sc.edu/PDB.