Invasion History

First Non-native North American Tidal Record: 1993
First Non-native West Coast Tidal Record: 1993
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Chorda asiatica is native to the east and west coasts of Japan, ranging from Kyushu to Hokkaido (Sasaki and Kawai 2007). Seaweeds of the genus Chorda have been historically unknown on the West Coast of the U.S., but a specimen was collected in Hood Canal, Puget Sound, Washington in 1993. Its identity was considered unclear, in part, because of a small number of specimens (Sasaki and Kawai 2007). However, a molecular study of the Hood Canal population found that these seaweeds were C. asiatica (Kawai et al. 2015).

North American Invasion History:

Invasion History on the West Coast:

Chorda sp. was first collected in Hood Canal, Puget Sound, Washington in 1993. The sample size was small and an initial analysis found it closest to C. kikonaiensis, a species with a very limited range in Hokkaido, Japan. However, Sasaki and Kawai (2007) considered the sample too small for morphological analysis or taxonomic conclusions. A more thorough study of the Hood Canal population identified it as C. asiatica (Kawai et al. 2015). It was growing on oyster shells on a muddy bottom, interspersed with Sargassum muticum, in waters of variable salinity. Chorda asiatica was probably introduced to Puget Sound with Pacific Oysters (Crassostrea gigas) from Japan (Kawai et al. 2015).


Description

Chorda asiatica grows from a small, discoid holdfast 1.5-3.5 mm in diameter. The thallus is an unbranched cord 1-2 m long (occasionally up to 5 m). The cortex is intermediate in thickness ranging between that of C. kikonaiensis and C. rigida. The alga has unilocular sporangia, which are sessile and narrowly ovate. The spores grow into microscopic, diecious, sexually dimorphic, oogamous gametophytes. Given the morphological simplicity of this seaweed, molecular identification is usually necessary. This description is based on: Golikov et al. 1976, Kawai et al. 2000, Sasaki and Kawai 2007, and Kawai et al. 2015.

Historically, Asian populations were considered conspecific with the northern Atlantic C. filum, found from the Arctic Ocean to New Jersey and Spain (Golikov et al. 1976; Guiry and Guiry 2016). However, studies of Asian populations have defined three native species in the Northwest Pacific, defined largely by molecular characteristics (Kawai et al. 2000; Sasaki and Kawai 2007; Kawai et al. 2015).


Taxonomy

Taxonomic Tree

Kingdom:   Plantae
Phylum:   Phaeophycophyta
Class:   Phaeophyceae
Order:   Laminariales
Family:   Chordaceae
Genus:   Chorda
Species:   asiatica

Synonyms

Potentially Misidentified Species

Chorda filum
(Linnaeus) Stackhouse 1797; Pacific populations were previously identified as this Atlantic species (e.g. Golikov et al. 1976; Kawai et al. 2015).

Chorda kikonaiensis
Sasaki & Kawai 2007; This species has a very limited distribution on the coast of Hokkaido along the Tsugaru Strait.

Chorda rigida
Kawai & Arai 2000; This species is known from Japan, China, Denmark, Sweden, and France. To our knowledge, it has not been designated as an invader in either Asia or Europe.

Ecology

General:

Chorda asiatica is a marine brown alga, which has a heteromorphic life cycle with microscopic gametophytes, which are dioecious and fuse to produce a sporophyte, and a sporophyte stage, which produces spores asexually (Bold and Wynne 1978; Sasaki and Kawai 2007). The genus Chorda is associated with cold, boreal waters, and is also tolerant of low salinity (Bold and Wynne 1978). Chorda asiatica is known from a temperature range of 5-20°C and 15 to 28+ PSU (Sasaki and Kawai 2007; Kawai et al. 2015). Chorda asiatica grows on shells, pebbles, and boulders, and on silt-clay bottoms (Golikov et al. 1976; Kawai et al. 2015).

Trophic Status:

Primary Producer

PrimProd

Habitats

General HabitatRockyNone
General HabitatUnstructured BottomNone
General HabitatOyster ReefNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone


Tolerances and Life History Parameters

Minimum Temperature (ºC)5Field, minimum temperature at collection site in Hood Canal, Puget Sound (Kawai et al. 2015)
Maximum Temperature (ºC)20Field, range at collection site in Hood Canal (Kawai et al. 2015).
Minimum Salinity (‰)15Field, range at collection site in Hood Canal, Puget Sound (Kawai et al. 2015)
Maximum Salinity (‰)35Typical marine salinity
Minimum Reproductive Temperature5Experimental. No growth at 2C (Sasaki and Kawai 2007)
Minimum Length (mm)1,000More typically 3000 (Guiry and Guiry 2016)
Maximum Length (mm)5,000More typically 3000 (Guiry and Guiry 2016)
Broad Temperature RangeNoneCold temperate-warm temperate
Broad Salinity RangeNonePolyhaline-euhaline

General Impacts

No economic or ecological impacts are known for Chorda asiatica in North American waters.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NWP-4a None 0 Native Estab
NWP-4b None 0 Native Estab
NWP-3b None 0 Native Estab
NWP-3a None 0 Native Estab
P290 Puget Sound 1993 Def Estab
NEP-III Alaskan panhandle to N. of Puget Sound 1993 Def Estab
NWP-5 None 0 Native Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude

References

Bold, Harold C.; Wynne, Michael J. (1978) Introduction to the Algae: Structure and Reproduction, Prentice-Hall, Englewood Cliffs, NJ. Pp. <missing location>

Collado-Vides, L. (2002) Morphological plasticity of Caulerpa prolifera (Caulerpales, Chlorophyta) in relation to growth form in a coral reef lagoon, Botanica Marina 45: 123-129

Golikov, A. N. and 7 other editors. (1976) <missing title>, Nauk, Leningrad. Pp. <missing location>

2004-2021 AlgaeBase. National University of Ireland Galway--http://algaebase.org

Kawai, Hiroshi; Hanyuda,Takeaki; Mumford, Thomas; Waaland, J. Robert (2015) An introduced population of Chorda asiatica (Chordaceae, Laminariales) in Puget Sound, Pacific coast of North America, Phycological Research 63: 154-158

Kawai, Hiroshi; Sasaki,Hideaki; Maeda, Yoshiki (2000) Morphology, life history, and molecular phylogeny of Chorda rigida, sp. nov. (Laminariales, Phaeophyceae) from the Sea of Japan and the genetic diversity of Chorda filum, Journal of Phycology 37: 130-142

Sasaki, Hideaki; Kawai, Hiroshi (2007) Taxonomic revision of the genus Chorda (Chordaceae, Laminariales) on the basis of sporophyte anatomy and molecular phylogeny, Phycologia 46(1): 10–-21