Non-Native Eelgrass: Zostera japonica
and Z. marina
mosaic. Z. japonica
shorter and darker eelgrass in the middle. Photo courtesy of Jeff Gaeckle, WA
Department of Natural Resources.
Dwarf eelgrass (Zostera japonica) is a
marine plant that is believed to have been introduced to
Washington from Japan. It exists in Puget Sound, Willapa Bay,
Grays Harbor, and along the outer coast. It has spread from Willapa
Bay as far south as California and as far north as Alaska.
Zostera japonica affects important shellfish growing areas
and appears to displace important ecological functions of mudflats
and other habitats. However, research has found that japonica also
provides many similar basic ecosystem functions as the native
eelgrass – Zostera marina. Given Z. japonica and Z. marina occur in
close proximity or in mixed beds, additional research is needed to
learn more about the risks to native habitats and shellfish beds
from Z. japonica, the beneficial ecological services it provides,
and potential management options that are protective of Z. marina.
Ecology participates in state agency discussions regarding study and responses to this non-native
- Administers a water quality permit for
the use of the aquatic herbicide imazamox on commercial clam
beds in Willapa Bay.
- Provides Shoreline Master Program guidance to local
governments. Ecology's current advice to local governments is
that projects should be reviewed on a case-by-case basis to determine if: 1) the project
site contains native and/or non-native eelgrass, 2) the project
will cause a loss of ecological functions, and 3) what
mitigation or project changes are needed to avoid impacts. Local
governments are encouraged to consult with state natural
resource agencies and base their project review on the most
current scientific information and studies. (See the
Shoreline Master Programs Handbook - Aquaculture Chapter.)
Meeting: The Science and Management of Zostera japonica, June 2013
To better understand the state’s role in managing this invasive aquatic
plant, the Departments of Ecology, Natural Resources,
and Fish and Wildlife, and the Washington State Invasive
Species Council co-sponsored a state meeting on June 18-19, 2013: The Science and Management of Zostera japonica in Washington. These
state resource agencies wanted to better understand the detrimental
and beneficial effects of Z. japonica – and what its continued
growth means for
Washington’s future. The meeting included presentations from
eelgrass experts and an analysis of the data and science by an
independent panel of scientists.
Some general conclusions that Ecology drew from the meeting are:
- Z. japonica is a non-native species.
- It exhibits many characteristics of an invasive plant (higher seed production, vegetative reproduction, greater tolerance to a range of environmental conditions).
- It is expanding its range north and south along the Pacific coast, and local populations are expanding in place.
- It is an ecosystem engineer and modifies habitats.
- Due to its non-native, invasive characteristics, Z. japonica
should not be protected as “critical saltwater habitat” as defined in
the shoreline master program guidelines [WAC 173-26-241(2)(c)]
- It provides many similar, basic ecosystem functions as native
eelgrass, including carbon sequestration.
- There should be a
multi-agency, collaborative approach to determine next steps in studying
and responding to this invasive aquatic plant.
Provided below are meeting materials and other resources related to
the meeting. Included is a summary report from a japonica science
workshop sponsored by the Department of Natural Resources and
Washington Sea Grant in September 2010. The science portion of this
June 2013 meeting built on the 2010 workshop.
Padilla Bay Technical Report No. 36,
Science Presentation Abstracts. Compiled by Dr. Douglas A.
Bulthuis, Padilla Bay Estuarine Research Reserve.
- Presentations - Day 1, June 18, 2013
Summary of 2010 Workshop, Dr. Jeff Gaeckle, WA Dept. of
What is Zostera japonica and Where did it come
from?, Dr. Jim Kaldy, US EPA
Role and growth of Zostera japonica in its Native
Range, Dr. Fred Short, WA Dept. of Natural Resources
Ecosystem Functions of the non-indigenous eelgrass,
Zostera japonica, in the Pacific Northwest, Dr. Doug Bulthuis, Padilla Bay National Estuarine Research Reserve
Z. japonica – effects on shellfish aquaculture,
Dr. Kim Patten, WSU Cooperative Extension
Interactions Between Zostera japonica and
Estuarine Fauna in the Pacific Northwest, Dr. Jennifer Ruesink, University of Washington
Interactions between Z. japonica and Z. marina,
Dr. Michael P. Hannam, University of Washington
Zostera japonica Scientific Panel Presentation. Summary
provided by Dr. Fred Short, Washington State Department of
The Current Regulatory Landscape for Zostera japonica in
Washington State, Revised Draft, July 1, 2013
Meeting notes: “Policy Discussion for State Agencies: The
challenges of managing Z. japonica and possible next steps”,
June 19 p.m. session. Notes provided by meeting facilitators.
Workshop 2010 Summary
Staff contact: Cedar Bouta, Shorelands and Environmental
Assistance Program, 360-407-6406