Short description of Caulacanthus okamurae, Pom-pom weed

Caulacanthus okamurae is a turf-forming red seaweed. It typically forms bright-red to red-brown springy hemispherical pom-poms up to 4 cm in diameter. There is no main axis, instead cartilaginous branches divide profusely and irregularly to form a tangled mass. Ultimate branches are short, curved and thorn-like. Individual branches are approximately 0.2 mm wide and are flattened oval in cross-section.

Impact summary: Caulacanthus okamurae, Pom-pom weed

It can form dense aggregations creating a dominant upper- to mid-intertidal algal turf on previously bare rock, creating a micro-habitat within which sand accumulates and moisture is retained. This habitat change can decrease the abundance of macro-invertebrates such as limpets, periwinkles and barnacles, but in turn, increase the number of algae, copepods and ostracods.

Habitat summary: Caulacanthus okamurae, Pom-pom weed

It occurs in the upper, middle and lower intertidal zones of moderately or very exposed rocky shores, growing as a loose irregular turf on bare rock and mussels, or mixed with other turf-forming seaweeds such as Gelidium spp. or Osmundea pinnatifida, or growing epiphytically on larger seaweeds such as Fucus serratus or Ulva lactuca. It has also been recorded from artificial structures such as harbour walls.  This alga has broad environmental tolerances, surviving at salinities from 18 to 40 psu and temperatures from below 5 to 27 degrees C. It has been recorded from both cold and warm temperate waters.

Overview table

Environment	Marine
Species status	Non-Native
Native range	Northwestern Pacific
Functional type	Algae (macroalgae)
Status in England	Non-Native
Status in Scotland	Non-Native
Status in Wales	Non-Native
Location of first record	Plymouth
Date of first record	2004

Origin

Native to the NW Pacific (Japan, Korea, and China) where it inhabits the upper intertidal zone of exposed rocky shores (Choi et al., 2001). The Pacific origin of populations in GB and Brittany was determined by molecular studies (Rueness & Rueness, 2000; Zuccarello et al., 2002; Mineur et al., 2006).

First Record

Initially identified as Caulacanthus ustulatus, the first record from the wild in GB is thought to be from Plymouth Sound, Devon in 2004 (Mineur et al., 2006; Brodie et al., 2014; Pederson et al., 2017)

Pathway and Method

Unintentional introduction with commercial oysters is the most likely explanation of the initial introduction to Brittany. Hull fouling and ballast water are likely vectors for its subsequent spread to GB and around Europe (Zuccarello et al., 2002; Mineur et al., 2014; Pederson et al., 2017)

Species Status

Caulacanthus okamurae and C. ustulatus were for some time grouped together as C. ustulatus due to difficulties distinguishing them morphologically (West & Calumpong, 1990). However, molecular studies of populations worldwide have since shown them to be distinct (Rueness & Rueness, 2000; Zuccarello et al., 2002; Mineur et al., 2006) Morphological differences in their reproductive structures have also been suggested (Choi & Nam, 2001). Caulacanthus ustulatus is considered to be native to the E Atlantic were it is widespread on shores including in SW France, Spain, Macronesia and W Africa.

Caulacanthus okamurae is an aggressive invader in the Eastern Pacific, being found all along the west coast of N America from the Gulf of California to Alaska (Pederson et al., 2017; Fofonoff et al., 2018).Within Europe, this species was first discovered around oyster farms in Roscoff, France in 1986 (Rio and Cabioc’h, 1988), then from Marseille in 2004, with its identity confirmed by molecular methods. It is now widespread in the Mediterranean where it co-exists with the native C. ustulatus (Mineur and Maggs, 2009; Verlaque et al., 2015). Subsequently, populations of C. okamurae were reported from the Netherlands in 2005 (Stegenga and Karremans, 2015), Belgium in 2011 (ICES, 2012) and Ireland in 2014 (NBNAtlas, 2018). It is now present on most European shores, from the Netherlands to Portugal, and throughout the Mediterranean Sea.

Dispersal Mechanisms

Floating fragments can be carried long distances

Reproduction

In GB most plants appear to be sterile so it is likely that reproduction is primarily vegetative by fragmentation and reattachment. C. okomurae has a two-phased life cycle with alternating tetrasporophyte (diploid) and gametophyte (haploid) plants that are similar in appearance, but no gametophytes have been observed in GB. Diploid plants develop tetrasporangia near the tips of branchlets, but require temperatures above 19 degrees C to produce germinating tetraspores. Cystocarps, the fruiting structures in haploid female plants, occur on the tips of branchlets, but again, only when sea temperatures are above 19 degrees C (Rueness, 1997; Choi and Nam, 2001; Verlaque et al., 2015; Bunker et al., 2017)

Known Predators/Herbivores

None known

Resistant Stages

None known, although Caulacanthus is adapted to withstand long periods of emersion.

Habitat Occupied in GB

In GB this species mainly occurs in the middle and lower intertidal zones of moderately or very exposed rocky shores, growing as a loose irregular turf on bare rock (including chalk reefs) or mussels, or mixed with other turf-forming seaweeds such as Gelidium spp. or Osmundea pinnatifida, or growing epiphytically on larger seaweeds such as Fucus serratus or Ulva lactuca. It has also been recorded from artificial structures such as harbour walls (Tittley, 2014; Bunker et al., 2017). 

Caulacanthus okamurae has a discontinuous distribution along the south coast of England, North Devon, Pembrokeshire and the east coast of Scotland. It is now common on many rocky shores in Cornwall, Devon, Sussex and Kent (Maggs et al., 2010; Tittley, 2014; NBNAtlas, 2018)

Environmental Impact

This species can create a novel turf habitat in the upper intertidal zone where turfs did not previously exist; algal turfs can increase habitat complexity, trap sediment, and maintain moisture during low tide which likely benefits meiofauna and seaweeds by providing food, habitat, or This species can create a novel turf habitat in the upper intertidal zone where turfs did not previously exist; algal turfs can increase habitat complexity, trap sediment, and maintain moisture during low tide which likely benefits meiofauna and seaweeds by providing food, habitat, or refuge from desiccation stress. In studies in California, it displaced macroinvertebrates, such as limpets, periwinkles, and barnacles, but supported increased numbers of copepods and ostracods, and of fleshy seaweeds, including Ulva, Gelidium, and Chondracanthus (Smith et al., 2014).In Kent, within the Thanet SAC, C. okamurae has carpeted areas of the chalk reefs, a designated feature of the SAC (Tittley, 2014).

Health and Social Impact

None known

Economic Impact

None known

Identification

Bunker, F. StP. D., Maggs, C. A., Brodie, J. A., Bunker, A. R. (2017). Seaweeds of Britain and Ireland. Second Edition. Wild Nature press, Plymouth, UK.

Choi, H. G., & Nam, K. W. (2001). Growth, tetrasporogenesis, and life history in culture of Caulacanthus okamurae (Gigartinales, Rhodophyta) from Korea. Botanica Marina, 44(4), 315-320.

Mineur, F., Maggs, C. A., & Verlaque, M. (2006). Molecular survey of the genera Gelidium and Caulacanthus on European shores: update on alien introductions. Poster presented at the 54th British Phycological Society meeting, Plymouth, January 2006.

Rueness, J., & Rueness, E. K. (2000). Caulacanthus ustulatus (Gigartinales, Rhodophyta) from Brittany (France) is an introduction from the Pacific Ocean. Cryptogamie Algologie, 21(4), 355-363.

West, J. A., & Calumpong, H. P. (1990). New records of marine algae from the Philippines. Micronesica, (2).

Zuccarello, G. C., West, J., & Rueness, J. (2002). Phylogeography of the cosmopolitan red alga Caulacanthus ustulatus (Caulacanthaceae, Gigartinales). Phycological research, 50(2), 163-172

Biology, ecology, spread, vectors

Brodie, J., Wilbraham, J., Pottas, J., & Guiry, M. (2016). A revised check-list of the seaweeds of Britain. Journal of the Marine Biological Association of the United Kingdom, 96(5), 1005-1029. doi:10.1017/S0025315415001484

Bunker, F. StP. D., Maggs, C. A., Brodie, J. A., Bunker, A. R. (2017). Seaweeds of Britain and Ireland. Second Edition. Wild Nature press, Plymouth, UK.

Choi, H. G., & Nam, K. W. (2001). Growth, tetrasporogenesis, and life history in culture of Caulacanthus okamurae (Gigartinales, Rhodophyta) from Korea. Botanica Marina, 44(4), 315-320.

Choi, H. G., Nam, K. W., & Norton, T. A. (2001). No whirlwind romance: typhoons, temperature and the failure of reproduction in Caulacanthus okamurae (Gigartinales, Rhodophyta). European Journal of Phycology, 36(4), 353-358.

Fofonoff, P. W., Ruiz, G. M., Steves, B., Simkanin, C., & Carlton, J. T. (2018). National Exotic Marine and Estuarine Species Information System. http://invasions.si.edu/nemesis/. Access Date: 7-Dec -2018

ICES. (2012). Report of the ICES Working Group on Introduction and Transfers of Marine Organisms WGITMO), 14 - 16 March 2012, Lisbon, Portugal. ICES CM 2012/ACOM:31. 301 pp.

Maggs, C., Mineur, F., Bishop J. and McCollin, T. (2010). Non-natives in MCCIP Annual Report Card 2010-11, MCCIP Science Review, 11pp. www.mccip.org.uk/arc

Mineur, F., Le Roux, A., Maggs, C. A., & Verlaque, M. (2014). Positive feedback loop between introductions of non-native marine species and cultivation of oysters in Europe. Conservation biology, 28(6), 1667-1676.

Mineur, F. & Maggs, C. 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

Mineur, F., Maggs, C. A., & Verlaque, M. (2006). Molecular survey of the genera Gelidium and Caulacanthus on European shores: update on alien introductions. Poster presented at the 54th British Phycological Society meeting, Plymouth, January 2006.

NBN Atlas website at http://species.nbnatlas.org/species/ NHMSYS0021060121 Accessed 15 November 2018.

Pederson, J. A., Gollasch, S., Laing, I., McCollin, T., Miossec, L., Occhipinti-Ambrogi, A., Wallentinus, I., & Werner, M. (2017). Status of introductions of non-indigenous marine species to the North Atlantic and adjacent waters 2003 – 2007. ICES Cooperative Research Report No. 334. 144 pp. http://doi.org/10.17895/ices.pub.1977

Rio, A., & Cabioch, J. (1988). Apparation du Caulacanthus ustulatus (Rhodophyta, Gigartinales) dans la Manche Occidentale. Cryptogamie Algol. 9: 231–4

Rueness, J. (1997). A culture study of Caulacanthus ustulatus (Caulacanthaceae, Gigartinales, Rhodophyta) from Europe and Asia. Cryptogamie, Algol, 2, 175-185.

Rueness, J., & Rueness, E. K. (2000). Caulacanthus ustulatus (Gigartinales, Rhodophyta) from Brittany (France) is an introduction from the Pacific Ocean. Cryptogamie Algologie, 21(4), 355-363.

Stegenga, H., & Karremans, M. (2015). Overzicht van de roodwier-exoten in de mariene wateren van Zuidwest-Nederland. Gorteria, 37(5), 141-157.

Tittley, I. (2014). Non-native marine algae in southeastern England. Porcupine Marine Natural History Society Bulletin, 1: Spring 2014, 28-32.

Verlaque, M., Ruitton, S., Mineur, F., & Boudouresque, C. F. (2015). CIESM Atlas of Exotic Species in the Mediterranean: Macrophytes. (See http://www.ciesm.org/atlas/appendix4.html)

Zuccarello, G. C., West, J., & Rueness, J. (2002). Phylogeography of the cosmopolitan red alga Caulacanthus ustulatus (Caulacanthaceae, Gigartinales). Phycological research, 50(2), 163-172.

Management and impact

Smith, J. R., Vogt, S. C., Creedon, F., Lucas, B. J., & Eernisse, D. J. (2014). The non-native turf-forming alga Caulacanthus ustulatus displaces space-occupants but increases diversity. Biological invasions, 16(10), 2195-2208.

Tittley, I. (2014).  Non-native marine algae in southeastern England. Porcupine Marine Natural History Society Bulletin, 1: Spring 2014, 28-32.

General

Fofonoff, P. W., Ruiz, G. M., Steves, B., Simkanin, C., & Carlton, J. T. (2018). National Exotic Marine and Estuarine Species Information System. http://invasions.si.edu/nemesis/. Access Date: 7-Dec -2018