Plant Assessment Form

Zostera japonica

Synonyms: Nanozostera japonica (Asch. & Graebn.) P. Toml. & U. Posl.

Common Names: dwarf eelgrass; Japanese eelgrass

Evaluated on: 5/18/11

List committee review date:

Re-evaluation date:

Evaluator(s)

Elizabeth Brusati, Program Manager
California Invasive Plant Council
1442-A Walnut St. #462, Berkeley, CA 94709
510-843-3902
edbrusati@cal-ipc.org
Joseph M. DiTomaso, Specialist in Cooperative Extension
Dept. of Plant Sciences, University of California-Davis
Mail Stop 4, One Shields Ave., Davis CA 95616
530-754-8715
jmditomaso@ucdavis.edu

No list committee members listed

General Comments

<p>This PAF is based on information provided by Kirsten Ramey with the California Department of Fish and Game, kramey@dfg.ca.gov, 707-445-5365. This species has many documented impacts in Oregon and Washington but due to its limited extent so far in California, there is not much data specific to California. Therefore, some questions are scored low because Z. japonica has not spread enough to create significant impacts here. However, impacts are likely to increase if populations expand and spread to new estuaries.</p>

Table 2. Criteria, Section, and Overall Scores

Overall Score? Moderate
Alert Status? Alert
Documentation? 3 out of 5
Score Documentation
1.1 ?Impact on abiotic ecosystem processes B Reviewed Scientific Publication
Impact?
Four-part score BCBD Total Score
B
1.2 ?Impact on plant community C. Minor Reviewed Scientific Publication
1.3 ?Impact on higher trophic levels B. Moderate Reviewed Scientific Publication
1.4 ?Impact on genetic integrity D. None Reviewed Scientific Publication
2.1 ?Role of anthropogenic and natural disturbance in establishment A. Severe Reviewed Scientific Publication
Invasiveness?
Total Points
13 Total Score B
2.2 ?Local rate of spread with no management B. Increases less rapidly Observational
2.3 ?Recent trend in total area infested within state B. Increasing less rapidly Observational
2.4 ?Innate reproductive potential
(see Worksheet A)
A. High Reviewed Scientific Publication
2.5 ?Potential for human-caused dispersal C. Low Observational
2.6 ? Potential for natural long-distance dispersal C. Rare Observational
2.7 ?Other regions invaded C. Already invaded Reviewed Scientific Publication
3.1 ?Ecological amplitude/Range
(see Worksheet C)
D. Narrow Reviewed Scientific Publication
Distribution?
Total Score D
3.2 ?Distribution/Peak frequency
(see Worksheet C)
D. Very low Observational

Table 3. Documentation

Scores are explained in the "Criteria for Categorizing Invasive Non-Native Plants that Threaten Wildlands".

Section 1: Impact
Question 1.1 Impact on abiotic ecosystem processes? B Reviewed Scientific Publication
Identify ecosystem processes impacted:

<p>Identify ecosystem processes impacted; Z. japonica colonizes intertidal mud and sand flats that lack permanent macrophyte cover (Harrison and Bigley 1982, Posey 1988, Thom 1990, Larned 2003). The physical structure of the mid to upper intertidal zones is altered where Z. japonica occurs, often forming a dense, sod-like root matrix that may completely cover the substrate surface (Posey 1988). The narrow blades trap fine sediments. Posey (1988) documented that particle size was significantly smaller in Z. japonica patches after six years. Larned (2003) documented changes in nutrient fluxes in Oregon estuaries after invasion by Z. japonica. The data demonstrate that Z. japonica invasions alter water column benthos nutrient fluxes. These alterations may in turn affect pelagic primary production. These impacts are based on studies from Oregon and Washington as not much information is available specifically from California but it seems likely that similar impacts may be occurring in Humboldt Bay (reviewer comment).</p>


Sources of information:

<p>Harrison and Bigley 1982, Larned 2003, Posey 1988, Thom 1990</p>


Question 1.2 Impact on plant community composition,
structure, and interactions?
C Reviewed Scientific Publication
Identify type of impact or alteration:

<p>Bando (2006) reported that in Washington, Z. japonica is also invading vegetated flats historically dominated by Zostera marina. Z. japonica generally occurs higher in the intertidal than the native eelgrass Z. marina, but the two are sometimes intermixed with each other and/or various algal species (Harrison 1982, Thom 1990, Baldwin and Lovvorn 1994a, Bulthuis 1995). Expansion of Z. japonica is characterized by rapid growth and spread during spring and summer (Harrison 1982). The species has become well established in estuaries throughout Washington and Oregon, covering thousands of acres (Baldwin and Lovvorn 1994a, Dudoit 2006). Scored lower because populations and impacts in California are currently limited.</p>


Sources of information:

<p>Bando 2006, Baldwin and Lovvorn 1994a, Bulthuis 1995, Dudoit 2006, Harrison 1982, Thom 1990</p>


Question 1.3 Impact on higher trophic levels? B Reviewed Scientific Publication
Identify type of impact or alteration:

<p>Substrate particle size affects which invertebrates can inhabit the sediment and this change in invertebrate community structure can impact shorebird populations that feed on invertebrates (Quammen 1984, Baldwin and Lovvorn 1994b, Danufsky and Colwell 2003). A decrease in the burrowing ghost shrimp (Neotrypaea californiensis) and other large epifauna was found in areas of Z. japonica in Washington (Harrison 1987, Posey 1988). N. californiensis is a favored prey for the long-billed curlew and found in the diets of the marbled godwit and willet (Dr. Nils Wornock, pers. comm., Point Reyes Bird Observatory). As Nanozostera japonica covers mudflats that otherwise lack permanent macrophyte cover, it could reduce the foraging areas needed by shorebirds. The estuaries Z. japonica is invading are important migration and wintering grounds for many birds.</p>


Sources of information:

<p>Baldwin and Lovvorn 1994b, CDFG 2009, Danufsky and Colwell 2003, Harrison 1987, Posey 1988, Quammen 1984</p>


Question 1.4 Impact on genetic integrity? D Reviewed Scientific Publication

<p>Nanozostera japonica is invading estuaries that contain native Zostera marina, although there is no information on hybridization.</p>


Sources of information:

<p>Kirsten Ramey, California Department of Fish and Game, Dean et al. (2008)</p>


Section 2: Invasiveness
Question 2.1 Role of anthropogenic and natural disturbance
in establishment?
B Observational
Describe role of disturbance:

<p>Often invades areas with little or no natural or human disturbance. A study conducted by Bando (2006) did show that Z. japonica displays a positive response to disturbance, which is particularly relevant to its invasion success, as tidal flats are dynamic systems that experience high levels of natural and anthropogenic disturbance, including bioturbation, coastal development, boating, shellfish culture, and in some regions (Washington), invasive smooth cordgrass (Spartina alterniflora) control.</p>


Sources of information:

<p>Bando 2006</p>


Question 2.2 Local rate of spread with no management? B Observational
Describe rate of spread:

<p>Z. japonica was discovered at the southwest end of Indian Island in Humboldt Bay, Humboldt County, California, in June 2002. In November 2006, Z. japonica was found near the Arcata Wastewater Treatment Plant in North Humboldt Bay. In March 2007, a fairly substantial population of Z. japonica at the Arcata Marsh, near the boat ramp at the foot of I Street in Arcata, CA, was found. In August 2007, a third new occurrence of Z. japonica growing on intertidal mudflats in Manila, CA, was discovered. On April 28, 2008, a new population of Z. japonica was discovered by a DFG crew in McNulty Slough in the Eel River estuary. McNulty Slough winds along the eastern boundary of the Department of Fish and Game Eel River Wildlife Area north of the mouth of the Eel River, Humboldt County, California.</p>


Sources of information:

<p>Kristen Ramey, California Department of Fish and Game</p>


Question 2.3 Recent trend in total area infested within state? B Observational
Describe trend:

<p>See information in question 2.2. Populations of the plant are expanding. A study by Shafer et al (2008) examined growth and productivity of Z. japonica at several points in its range on the Pacific Coast of North America and concluded that southern populations may be better adapted to warmer conditions than northern populations, suggesting that Z. japonica could expand further south in California.</p>


Sources of information:

<p>Kirsten Ramey, California Department of Fish and Game, Shafer et al. 2008</p>


Question 2.4 Innate reproductive potential? A Reviewed Scientific Publication
Describe key reproductive characteristics:

<p>It is an annual, overwintering as buried seeds, or a short-lived perennial (Harrison 1982). Z. japonica reproduces vegetatively through rhizomatous cloning and sexually through seed production (Phillips 1984).</p>


Sources of information:

<p>Harrison 1982, Phillips 1984</p>


Question 2.5 Potential for human-caused dispersal? C Observational
Identify dispersal mechanisms:

<p>Z. japonica likely arrived on the Pacific Coast of North America coincident with the introduction of oysters from Japan as packing material or as seed on oyster shell (Harrison and Bigley 1982). The introduction of Z japonica to Humboldt Bay was NOT likely associated with oyster culture, as oyster larvae imported here come from hatcheries. The method of introduction into Humboldt Bay is unknown. The detection of Z. japonica in Humboldt Bay, California, in June 2002 represents the first time this introduced species has been encountered in California. The method of spread around Humboldt Bay and to McNulty Slough is unknown, however, two locations of invasion have been at small public boat ramps which may suggest that plant material or seeds can be dispersed in mud stuck to boat hulls, boots and gear.</p>


Sources of information:

<p>Kirsten Ramey, California Department of Fish and Game, CDFG 2009</p>


Question 2.6 Potential for natural long-distance dispersal? C Observational
Identify dispersal mechanisms:

<p>The widespread and ongoing dispersal, both within and between estuaries, may be aided by waterfowl species such as Brant geese. The Brant diet includes substantial amounts of Z. japonica, suggesting it is likely that the small goose has become a vector for dispersal of the non-native eelgrass. The possibility that Brant are capable of transporting viable Z. japonica seeds in their guts is being further explored by researches at Oregon State University.</p>


Sources of information:

<p>Kirsten Ramey, California Department of Fish and Game</p>


Question 2.7 Other regions invaded? C Reviewed Scientific Publication
Identify other regions:

<p>Z. japonica was first detected in Washington in 1957 (Hitchcock et al. 1969), in British Columbia in 1969 (Harrison and Bigley 1982), and in Oregon in 1975 (Posey 1988). As an intertidal and subtidal plant, it is restricted to only one ecological type.</p>


Sources of information:

<p>Harrison and Bigley 1982, Hitchcock et al. 1969, Posey 1988</p>


Section 3: Distribution
Question 3.1 Ecological amplitude/Range? D Reviewed Scientific Publication

Z. japonica was discovered at the southwest end of Indian Island in Humboldt Bay, Humboldt County, California, in June 2002. In November 2006, Z. japonica was found near the Arcata Wastewater Treatment Plant in North Humboldt Bay. In March 2007, a fairly substantial population of Z. japonica at the Arcata Marsh, near the boat ramp at the foot of I Street in Arcata, CA, was found. In August 2007, a third new occurrence of Z. japonica growing on intertidal mudflats in Manila, CA, was discovered. On April 28, 2008, a new population of Z. japonica was discovered by a DFG crew in McNulty Slough in the Eel River estuary. McNulty Slough winds along the eastern boundary of the Department of Fish and Game Eel River Wildlife Area north of the mouth of the Eel River, Humboldt County, California. It inhabits mud flats between low and semi-high tide marks.


Sources of information:

Kirsten Ramey, California Department of Fish and Game,


Question 3.2 Distribution/Peak frequency? D Observational
Describe distribution:

Currently limited to Humboldt County. However, Shafer et al (2008) examined growth and productivity of Z. japonica at several points in its range on the Pacific Coast of North America and concluded that southern populations may be better adapted to warmer conditions than northern populations, suggesting that Z. japonica could expand further south in California.


Sources of information:

Kirsten Ramey, California Dept. of Fish and Game; Shafer et al. 2008


Worksheet A - Innate reproductive potential

Reaches reproductive maturity in 2 years or less Yes
Dense infestations produce >1,000 viable seed per square meter Unknown
Populations of this species produce seeds every year. Yes
Seed production sustained over 3 or more months within a population annually Unknown
Seeds remain viable in soil for three or more years Unknown
Viable seed produced with both self-pollination and cross-pollination Unknown
Has quickly spreading vegetative structures (rhizomes, roots, etc.) that may root at nodes Yes
Fragments easily and fragments can become established elsewhere Yes
Resprouts readily when cut, grazed, or burned Yes
Total points: 6
Total unknowns: 4
Total score: A?

Related traits:

Worksheet B - Arizona Ecological Types is not included here

Worksheet C - California Ecological Types

(sensu Holland 1986)
Major Ecological Types Minor Ecological Types Code?
Marine Systemsmarine systems
Freshwater and Estuarine lakes, ponds, reservoirs
Aquatic Systemsrivers, streams, canals
estuariesD, < 5%
Dunescoastal
desert
interior
Scrub and Chaparralcoastal bluff scrub
coastal scrub
Sonoran desert scrub
Mojavean desert scrub (incl. Joshua tree woodland)
Great Basin scrub
chenopod scrub
montane dwarf scrub
Upper Sonoran subshrub scrub
chaparral
Grasslands, Vernal Pools, Meadows, and other Herb Communitiescoastal prairie
valley and foothill grassland
Great Basin grassland
vernal pool
meadow and seep
alkali playa
pebble plain
Bog and Marshbog and fen
marsh and swamp
Riparian and Bottomland habitatriparian forest
riparian woodland
riparian scrub (incl.desert washes)
Woodlandcismontane woodland
piñon and juniper woodland
Sonoran thorn woodland
Forestbroadleaved upland forest
North Coast coniferous forest
closed cone coniferous forest
lower montane coniferous forest
upper montane coniferous forest
subalpine coniferous forest
Alpine Habitatsalpine boulder and rock field
alpine dwarf scrub
Amplitude (breadth): D
Distribution (highest score): D

Infested Jepson Regions

Click here for a map of Jepson regions

  • Northwest