Invasion History

First Non-native North American Tidal Record: 1961
First Non-native West Coast Tidal Record: 1961
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Caulacanthus ustulatus (Kutzing 1843) was described from Cadiz, Spain, but was believed to have a cosmopolitan range in the Eastern Atlantic (France-South Africa) and the Indo-West Pacific (South Africa-Japan, and east to Australia, New Zealand, and Hawaii). A molecular analysis indicates that this 'species' contained two major lineages, an Indo-West Pacific lineage and an Atlantic lineage (Zuccarello et al. 2002). The name C. okamurae Yamada 1933 was used for populations from the Northwest Pacific by many Asian workers, but there was doubt about the validity of the name, and the distinctiveness of the species. Observations of the reproductive structures of C. okamurae support its status as a separate species (Choi and Nam 2001; Choi et al. 2001; Verlaque et al. 2015; Guiry and Guiry 2017). Caulacanthus okamurae is known from Japan, China, Korea, Taiwan, and Yonaguni Island, a Japanese island near Taiwan (Choi et al. 2001; Zuccarello et al. 2002; Guiry and Guiry 2017).

North American Invasion History:

Invasion History on the West Coast:

Caulacanthus okamurae is an invader in the Eastern Pacific, being found in the Gulf of California in 1944; Pacific Baja California in 1961; British Columbia in 1974; San Pedro, California (CA) in 1999; and Prince William Sound, Alaska sometime from 1989-1996 (Gabrielson and Scagel 1999; Lindstrom et al. 1999; Rueness and Rueness 2000; Whiteside and Murray 2004; Miller et al. 2011). In southern California, Caulacanthus has been observed at numerous sites during the last decade (S. Murray, personal communication), but was not recorded 30 years ago during extensive intertidal surveys sponsored by the government (Murray & Littler, 1981), nor 40 years ago when E.Y. Dawson conducted extensive surveys (Dawson, 1959). This alga was found at Point La Jolla and Dana Point, CA in 2004 (Maloney et al. 2006); Corona del Mar and Point Fermin, CA in 2010 (Smith et al. 2014); and Elkhorn Slough, CA (deRivera et al. 2005; Blanchette et al. 2008). It is also known from locations in central California, including: Santa Cruz, San Francisco Bay (Miller, 2004), and Tomales Bay (specimens from the University of California); and it appears to be spreading northward (Miller et al. 2011).

In the Strait of Georgia, it is known from the Redondo Islands, Pendrell Sound, British Columbia (first reported in 1974; Gabrielson and Scagel 1989) to the San Juan Islands, Washington (first reported in 1995; Zucarello et al. 2002). In surveys run from 1989 to 1996 in Prince William Sound, Alaska, C. okamurae (as C. ustulatus) was found at one location – Hogg Bay (Lindstrom et al. 1999). Vectors on the West Coast probably include hull-fouling, ballast water, and oyster-culture.

Invasion History Elsewhere in the World:

Caulacanthus okamurae was reported in 2004 in Brittany, France. Populations of C. ustulatus from Brittany were grouped with the Pacific lineage in the plastid and mitochondrial DNA analysis (Rueness and Rueness 2000; Zuccarello et al. 2002). Subsequently, populations of C. okanmurae were found in Belgium in 2011 (Kerckhof et al., in ICES Advisory Committee on the Marine Environment 2012), the Netherlands in 2005 (Stegenga and Karremans 2015), and the south coast of England in 2000-2005 (Brodie et al. 2016). In the Mediterranean, C. okamurae was found in Marseille in 2004 and later at Toulon, with its identity confirmed by molecular methods (Mineur and Maggs 2005; Verlaque et al. 2015).


Caulacanthus okamurae reaches 20-30 mm in height, forming dense, low turf in the intertidal zone. The branching is irregular to sub-dichotomous, with the smallest branches curved or spine-like. The plants are attached by multicellular holdfasts to the substrate. Cystocarps (fruiting structures in haploid female plants, 300-500 µm in diameter) occur on the tips of the finest branchlets. The cystocarps of C. okamurae lack the spines which occur in C. ustulatus. Diploid tetrasporophyte plants have tetrasporangia, which occur as swellings in the spine-like branchlets (Choi and Nam 2001; Verlaque et al. 2015). Identification of C. okamurae, and distinction from C. ustulatus, requires microscopic and/or molecular examination.

Most populations of Caulacanthus spp. have been traditionally identified as C. ustulatus (Kutzing 1843) described from Spain, and widespread on Eastern Atlantic shorelines. A distinct form from Japan (C. okamurae Yamada 1933) was found elsewhere in the Northwest Pacific (Choi and Nam 2001; Choi et al. 2001). The status of C. okamurae has been disputed, partly on nomenclatural grounds, but a genetic analysis found that Northwest Pacific populations were genetically distinct from those in the Atlantic (Zuccarello et al. 2002). Reproductive structures, needed for comparison of the populations, are rare in Asian populations, possibly by stress due to seasonal typhoons. However, cultured specimens show morphologically distinct structures (Choi and Nam 2001; Choi et al. 2001). Extenisive mitdochondrial DNA analysis found that Caulacanthus sp. from Moss Landinfg were conspecific with specimens from Korea, France, and Spain (Hartnell College Genomics Group et al. 2020),


Taxonomic Tree

Kingdom:   Plantae
Phylum:   Rhodophycota
Class:   Rhodophyceae
Subclass:   Florideophycideae
Order:   Gigartinales
Family:   Rhabdoniaceae
Genus:   Caulacanthus
Species:   okamurae


Caulacanthus ustulatus (Pacific lineage) ((Mertens ex Turner) Kützing, 1843)

Potentially Misidentified Species

Caualcanthus ustulatus
Described from Cadiz, Spain, broad Eastern Atlantic distribution



Caulacanthus okamurae has a two-phased life cycle, with haploid gametophytes, producing carpospores, and diploid tetrosporophytes, producing haploid tetrospores. However, in Korea, where it is native, the reproductive stages are rarely seen, and most of the plants reproduce vegetatively. In culture, temperatures above 19°C were required for sexual reproduction, but in the field, in Busan, South Korea, these temperatures were reached only in September, a season of extensive typhoons, which severely damaged the plants (Choi and Nam 2001; Choi et al. 2001).

Caulacanthus okamurae is a low-growing mat-forming red alga that can grow in dense turfs on the mid-to-upper intertidal zone of exposed rocky coasts as well as in sheltered areas (Gabrielson and Scagel 1989; Choi and Nam 2001; Choi et al. 2001; Whiteside and Murray 2004; Smith et al. 2014). Caulacanthus okamurae grew well at 13-27°C, at 8 to 16 hours of light per day, and 20-16 µE m-3s-1 (Choi and Nam 2001).

Trophic Status:

Primary Producer



General HabitatRockyNone
General HabitatOyster ReefNone
General HabitatMarinas & DocksNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeMid IntertidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Maximum Temperature (ºC)27Highest tested, in culture, Korea (Choi and Nam 2001)
Minimum Reproductive Temperature19For sexual reproduction, in culture, Korea (Choi and Nam 2001)
Maximum Height (mm)30Cho and Nam 2001
Broad Temperature RangeNoneCold temperate-Warm-temperate (Introduced from)
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

Turf-forming algae are common in the intertidal zones of tropical regions, but are rare in temperate regions. Caulacanthus okamurae has become a local dominant in mid-intertidal algal turf communities in southern California (Whiteside and Murray 2004; Blanchette et al. 2008; Smith et al. 2014). This dense, low turf habitat decreased the number of larger intertidal fauna (periwinkles, limpets, barnacles), but favored meiofauna (copepods and ostracods) and larger fleshy seaweeds by retaining water and decreasing desiccation (Whiteside and Murray 2004; Smith et al. 2014).

Regional Impacts

NEP-VIPt. Conception to Southern Baja CaliforniaEcological ImpactHabitat Change
Caulacanthus okamurae has become a local dominant in mid-intertidal algal turf communities in southern California (Whiteside and Murray 2004; Smith et al. 2014.) Blanchette et al. (2008) found that C. okamurae had an average of ~5-10% cover at sites from Paradise Cove to Point Fermin, but did not note its occurrence elsewhere in a survey of rocky intertidal communities from San Diego to Alaska. At five sites in southern California (Dana Point, Shaw's Cove, Corona del Mar, Point Fermin, and Point Fermin North), C. okamurae often formed dense patches of low turf exceeding 40% cover. This turf displaced macroinvertebrates, such as limpets, periwinkles, and barnacles, but supported an increased number of copepods and ostracods, and of fleshy seaweeds, including Ulva, Gelidium, and Chondracanthus. The dense turf may restrict movements of larger animals, and settlement and feeding of barnacles, but also retains water and reduces desiccation (Smith et al. 2014).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEA-IV None 1988 Def Estab
NWP-4a None 0 Native Estab
NWP-3a None 0 Native Estab
NWP-3b None 0 Native Estab
NWP-4b None 0 Native Estab
NEP-VI Pt. Conception to Southern Baja California 1961 Def Estab
NEP-I Alaska north of the Aleutians 1996 Def Estab
NEP-III Alaskan panhandle to N. of Puget Sound 1974 Def Estab
NEP-V Northern California to Mid Channel Islands 2003 Def Estab
P056 _CDA_P056 (Los Angeles) 1999 Def Estab
P027 _CDA_P027 (Aliso-San Onofre) 2004 Def Estab
P022 _CDA_P022 (San Diego) 2004 Def Estab
P080 Monterey Bay 2005 Def Estab
P090 San Francisco Bay 2003 Def Estab
P292 _CDA_P292 (San Juan Islands) 1995 Def Estab
P110 Tomales Bay 2011 Def Estab
NEA-II None 2005 Def Estab
P040 Newport Bay 2010 Def Estab
MED-II None 2004 Def Estab
P105 _CDA_P105 (Tomales-Drakes Bay) 2015 Def Estab
NEA-V None 0 Def Estab
NEA-III None 2014 Def Estab
MED-IV None 2012 Def Estab
MED-VI None 2002 Def Estab
P058 _CDA_P058 (San Pedro Channel Islands) 2019 Def Estab
MED-VII None 2014 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


California Department of Fish and Wildlife (2014) Introduced Aquatic Species in California Bays and Harbors, 2011 Survey, California Department of Fish and Wildlife, Sacramento CA. Pp. 1-36

Choi, H. G.; Nam, K. W. (2001) Growth, tetrasporogenesis, and life history in culture of Caulacanthus okamurae (Gigartinales, Rhodophyta) from Korea, Botanica Marina 44: 315-320

Choi, Han Gil; Nam, Ki Wan; Norton, Trevor A. (2001) No whirlwind romance: typhoons, temperature and the failure of reproduction in Caulacanthus okamurae (Gigartinales, Rhodophyta), European Journal of Phycology 36: 353-358

David, Andrew A.; Cote, Sara C. (2019) Genetic evidence confirms the presence of the Japanese mystery snail, Cipangopaludina japonica (von Martens, 1861) (Caenogastropoda: Viviparidae) in northern New York, BioInvasions Records 8: 793-803

de Rivera, Catherine, and 27 authors (2005) Broad-scale non-indigenous species monitoring along the West Coast in National Marine Sanctuaries and National Estuarine Research Reserves report to National Fish and Wildlife Foundation, National Fish and Wildlife Foundation, Washington, D.C.. Pp. <missing location>

Gabrielson, Paul W.; Scagel, Robert F. (1989) The marine algae of British Columbia, northern Washington, and southeast Alaska: divison Rhdophyta (red algae), class Rhodophyceae, order Gigartinales, family Caulacanthaceae and Plocamiaceae., Canadian Journal of Botany 67: 1221-1234

Guiry, M. D.; Guiry, G. M. 2004-2023 AlgaeBase. National University of Ireland Galway--

ICES Advisory Committee on the Marine Environment (2012) <missing title>, International Council for the Exploration of the Seas, Copenhagen. Pp. <missing location>

Lee, Hae-Bok; Lee, Jan Wan; Choi, Han Gu; Lee, Wook Jae; Kim, Jong-In (2001) Morphology and rbcL sequences of Caulacanthus okamurae Yamada (Gigartinales, Rhodophyta) from Korea, Algae 16(1): 25-34

Lindstrom, S. C.; Houghton, J. P; Lees, D. C. (1999) Intertidal macroalgal community structure in southwestern Prince William Sound, Alaska., Botanica Marina 42: 265-280

Looby, Audrey; Ginsburg, David W. (2021) Nearshore species biodiversity of a marine protected area off Santa Catalina Island, California, Western North American Naturalist 81(1): 113-130

Maloney, E.; Fairey, R.; Lyman, A.; Reynolds, K.; Sigala, M. (2006) <missing title>, California Department of Fish and Game, Office of Spill Prevention and Response, Sacramento. Pp. <missing location>

Miller, Kathy Ann (2004) California's non-native seaweeds, Fremontia 32(1): 10-15

Miller, Kathy Ann; Aguilar-Rosas, Luis Ernesto; Pedroche, Francisco F. (2011) A review of non-native seaweeds from California, USA and Baja California, Mexico, Hidrobiológica 21(3): 365-379

Mineur, Frederic; Maggs, Christine A. (2009) Green and red aliens: applying herbarium collections in molecular, morphological and geographical investigations of the genera Ulva, Codium, Caulacanthus and Feldmannophycus, The Phycologist 76: 5

Oliveira, Otto M. P. and 24 authors (2016) Census of Cnidaria (Medusozoa) and Ctenophora from South American marine waters, Zootaxa 4194: 1-256

Pister, Benjamin (2009) Urban marine ecology in southern California: the ability of riprap structures to serve as rocky intertidal habitat, Marine Biology 156: 861-873

Rueness, Jan; Rueness, Eli K. (2000) Caulacanthus ustulatus (Gigartales, Rhodophyta) from Brittany, France is an introduction.from the Pacific Ocean., Cryptogamie - Algologie 21(4): 355-363

Ruiz, Gregory M.; Geller, Jonathan (2018) Spatial and temporal analysis of marine invasions in California, Part II: Humboldt Bay, Marina del Re, Port Hueneme, and San Francisco Bay, Smithsonian Environmental Research Center & Moss Landing Laboratories, Edgewater MD, Moss Landing CA. Pp. <missing location>

Smith, Jayson R.; Vogt, Sean C.; Creedon, Faye; Lucas, Benjamin J.; Eernisse, Douglas J. (2014) The non-native turf-forming alga Caulacanthus ustulatus displaces space-occupants but increases diversity, Biological Invasions 16(10): 2195-2208

Stegenga, Herre; Karremans, Mart (2015) [Review of the red algal exotics in the marine waters of the Southwest Netherlands], Gorteria 27: 141-157

Tsuda, Roy T. ; Abbott, Isabella A.; Vroom, Peter S.; Fisher, Jack R. (2010) Marine benthic algae of Johnston Atoll: New species records, spatial distribution, and taxonomic affinities with neighboring islands, Pacific Science 64(4): 585-605

Whiteside, K. E.; Murray, S. N. (2004) Spatial and temporal patterns of abundance in southern California populations of Caulacanthus ustulatus (Rhodophyta)., Journal of Phycology 40(8): 14

Zuccarello, Giuseppe; West, John; Rueness, Jan. (2002) Phylogeography of the cosmopolitan red alga Caulacanthus ustulatus (Caulacanthaceae, Gigartinales)., Phycological Research 50: 163-172.