Invasion HistoryFirst 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).
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).
Potentially Misidentified Species
(Linnaeus) Stackhouse 1797; Pacific populations were previously identified as this Atlantic species (e.g. Golikov et al. 1976; Kawai et al. 2015).
Sasaki & Kawai 2007; This species has a very limited distribution on the coast of Hokkaido along the Tsugaru Strait.
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.
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).
|General Habitat||Unstructured Bottom||None|
|General Habitat||Oyster Reef||None|
|Salinity Range||Polyhaline||18-30 PSU|
|Salinity Range||Euhaline||30-40 PSU|
Tolerances and Life History Parameters
|Minimum Temperature (ºC)||5||Field, minimum temperature at collection site in Hood Canal, Puget Sound (Kawai et al. 2015)|
|Maximum Temperature (ºC)||20||Field, range at collection site in Hood Canal (Kawai et al. 2015).|
|Minimum Salinity (‰)||15||Field, range at collection site in Hood Canal, Puget Sound (Kawai et al. 2015)|
|Maximum Salinity (‰)||35||Typical marine salinity|
|Minimum Reproductive Temperature||5||Experimental. No growth at 2C (Sasaki and Kawai 2007)|
|Minimum Length (mm)||1,000||More typically 3000 (Guiry and Guiry 2016)|
|Maximum Length (mm)||5,000||More typically 3000 (Guiry and Guiry 2016)|
|Broad Temperature Range||None||Cold temperate-warm temperate|
|Broad Salinity Range||None||Polyhaline-euhaline|
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|
|NEP-III||Alaskan panhandle to N. of Puget Sound||1993||Def||Estab|
ReferencesBold, 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>
Guiry, M. D.; Guiry, G. M. 2004-2023 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