Melanothamnus harveyi - Harvey's siphon weed

There are two possible locations where this species may come from. The first possibility is that Harvey's siphon weed got introduced to the Atlantic Ocean from the Pacific Ocean. Another hypothesis is that M. harveyi is indigenous to our regions. As there is insufficient evidence to contradict the first hypothesis, the species is assumed to be exotic to our regions ^[2].

First observation in Belgium

In 2000, Harvey's siphon weed was first reported in Belgian waters in the Sluice Dock of Ostend ^[3].

Spreading in Belgium

Harvey's siphon weed was observed abundantly in the Sluice Dock of Ostend in 2000. This seaweed was also found in 2007 ^[4].

Spreading in neighbouring countries

Around 1832, this exotic species was first spotted in Europe along the coasts of western France as Polysiphonia insidiosa, an erroneous name ^{[5, 6]}. It may have been introduced to Britain from France, where it was first observed in 1908 near Weymouth, a peninsula in southern Britain ^[7].

In the Netherlands, the species was observed for the first time in 1960 in the Canal through Zuid-Beveland ^[7]. Currently, Harvey's siphon weed can also be found in various in the Wadden Sea ^[8], Lake Grevelingen, the Eastern Scheldt ^[9] and ‘Veerse Meer’ (Lake Veere) ^[7].

Today, populations of Harvey’s siphon weed can be found in Europe from Norway to the Mediterranean Sea, including the east coasts of Great Britain and Ireland ^[10]

There is no certainty about how Harvey’s siphon weed arrived in Europe. Primary introduction of this red seaweed may have taken place via the import of oyster broodstock from Japan since this species is known to attach to oysters ^[10]. Alternatively, biofouling on other non-native algae (e.g. Japanese wireweed Sargassum muticum and dead man’s fingers Codium fragile) brought from Japan might have also contributed to its primary introduction ^[7].

Once it arrived in Europe, the species may have dispersed in several ways. A first possible dispersal mechanism is biofouling on other non-indigenous algae; species characterised by a high buoyancy and drift capacity, allowing them to easily spread along coastal areas ^[7]. Secondly, artificial floating substrates such as fish traps, ropes and boat hulls can also facilitate the spread of weeds ^[7]. Finally, heavy traffic of recreational yachts between marinas may have caused the further spread of this red alga ^[11].

Harvey’s siphon weed grows and reproduces quickly. The spores of this red seaweed can survive for a long time in unfavourable conditions and develop when conditions improve ^[7].

In an environment where seaweeds are heavily grazed, Harvey’s siphon weed is often one of the few species that can survive ^[7]. This is probably because, like other related species of algae, it forms chemical substances that work as a repellent against grazers ^[7].

This exotic species lives in locations with varying salt concentrations. For example, in the Dutch Wadden Sea, the species is found at various locations with salinity ranging from 19 to 31 PSU ^[8]. By comparison, the North Sea – where the species is also present – has a salinity of approximately 35 PSU.

Harvey’s siphon weed tolerates large temperature fluctuations. Experiments show that this red seaweed can reproduce at temperatures varying between 4-22°C ^[12]. In the near future, due to global warming, one expects reduced photosynthesis because of higher temperatures. In combination with the acidification of seawater (due to higher levels of CO₂), it appears that these negative effects are alleviated. Therefore, global warming will hardly impact the dispersal capacity of M. harveyi ^[13].

In Belgium, the Netherlands and Great Britain, similar effects related to the introduction of this exotic species have been observed. In some places, the native seaweed flora got replaced by non-native seaweeds. At these locations, M. harveyi was often observed growing on other algae ^{[4, 14]}. Harvey’s siphon weed may contribute to the displacement of native species because of its high growth rate ^[10]. Economic damage is small ^[10] and so far, no measures have been taken to remove this species ^[10].

Harvey’s siphon weed grows 10-15cm in height but is often smaller. It is a strongly branched, brownish-red seaweed, mainly found on other organisms such as oysters and seaweed (e.g. dead man’s fingers or Japanese wireweed) and artificial substrates such as ropes and pontoons.  Since this species might use another plant as a substrate, it is called an epiphyte. Harvey’s siphon weed might serve itself as a substrate for other organisms (such as the non-indigenous red algae Antithamnionella sp.) ^[4].

The species is common in harbours, pools and saline inland waters. It is found both low in the intertidal zone and at depths of approximately three metres. It prefers areas protected from the action of waves (in harbours) but can be found along the coast in areas with moderate wave action ^{[7, 15]}.

Red algae of the genus Melanothamnus can only be determined using a microscope because the species are almost indistinguishable to the naked eye. A conclusion can only be made based on the microscopic structures of the seaweed ^[11]. There is often confusion between the species Melanothamnus harveyi and Melanothamnus japonica. Genetic analysis showed that they are indeed two different species ^[2].

[1]          World Register of Marine Species (WoRMS) (2020). Melanothamnus harveyi (Bailey) Díaz-Tapia & Maggs, 2017. [http://www.marinespecies.org/aphia.php?p=taxdetails&id=1027787] (2020-11-18).

[2]          Savoie, A.M.; Saunders, G.W. (2015). Evidence for the introduction of the Asian red alga Neosiphonia japonica and its introgression with Neosiphonia harveyi (Ceramiales, Rhodophyta) in the Northwest Atlantic. Mol. Ecol. 24(23): 5927-5937. [http://www.vliz.be/nl/catalogus?module=ref&refid=302039]

[3]          Kerckhof, F.; Haelters, J.; Gollasch, S. (2007). Alien species in the marine and brackish ecosystem: the situation in Belgian waters. Aquat. Invasions 2(3): 243-257. [http://www.vliz.be/en/imis?module=ref&refid=114365]

[4]          Heytens, M.; De Clerck, O.; Coppejans, E. (2007). Studie van macrowiergemeenschappen van de Spuikom van Oostende in functie van de Kaderrichtlijn water. Universiteit Gent - Vakgroep Biologie - Afdeling Algologie: Gent. 65 pp. [http://www.vliz.be/en/imis?module=ref&refid=118621]

[5]          Maggs, C.A.; Hommersand, M.H. (1993). Seaweeds of the British Isles: Volume 1 Rhodophyta. Part 3A Ceramiales. Seaweeds of the British Isles, 1. Natural History Museum: London. ISBN 1-898298-81-5. 444 pp. [http://www.vliz.be/en/imis?module=ref&refid=65109]

[6]          McIvor, L.; Maggs, C.A.; Provan, J.; Stanhope, M.J. (2001). rbcL sequences reveal multiple cryptic introductions of the Japanese red alga Polysiphonia harveyi. Mol. Ecol. 10(4): 911-919. [http://www.vliz.be/imis/imis.php?module=ref&refid=206837]

[7]          Maggs, C.A.; Stegenga, H. (1999). Red algal exotics on North Sea coasts. Helgol. Meeresunters. 52: 243-258. [http://www.vliz.be/en/imis?module=ref&refid=110857]

[8]          Gittenberger, A.; Rensing, M.; Stegenga, H.; Hoeksema, B. (2010). Native and non-native species of hard substrata in the Dutch Wadden Sea. Ned. Faunist. Meded. 33: 21-76. [http://www.vliz.be/en/imis?module=ref&refid=206549]

[9]          Stegenga, H. (2002). De Nederlandse zeewierflora: van kunstmatig naar exotisch? Het Zeepaard 62(1): 13-24. [http://www.vliz.be/imis/imis.php?module=ref&refid=22955]

[10]        Eno, N.C.; Clark, R.A.; Sanderson, W.G. (Ed.) (1997). Non-native marine species in British waters: a review and directory. Joint Nature Conservation Committee: Peterborough. ISBN 1-86107-442-5. 152 pp. [http://www.vliz.be/nl/imis?module=ref&refid=24400]

[11]        Kerckhof, F.; Stegena, H. (2003). Nieuwe Polysiphonia-soorten voor België en Noord-Frankrijk, met een gereviseerde determineertabel voor de soorten van het geslacht Polysiphonia in deze regio. Dumortiera 80: 40-45. [http://www.vliz.be/imis/imis.php?module=ref&refid=38761]

[12]        Koch, C. (1986). Attempted hybridization between Polysiphonia fibrillosa and P. violacea (Bangiophyceae) from Denmark; with culture studies primarily on P. fibrillosa. Nord. J. Bot. 6(1): 123-128. [http://www.vliz.be/imis/imis.php?module=ref&refid=206897]

[13]        Olischläger, M.; Wiencke, C. (2013). Ocean acidification alleviates low-temperature effects on growth and photosynthesis of the red alga Neosiphonia harveyi (Rhodophyta). J. Exp. Bot. 64(18): 5587-5597. [http://www.vliz.be/nl/catalogus?module=ref&refid=302040]

[14]        Stegenga, H.; Prud'homme van Reine, W.F. (1998). Changes in the seaweed flora of the Netherlands, in: Scott, G.W. et al. Changes in the marine flora of the North Sea. Centre for European Research into Coastal Issues (CERCI): Scarborough: pp. 77-87. [http://www.vliz.be/imis/imis.php?module=ref&refid=205502]

[15]        Stegenga, H.; Mol, I. (1983). Flora van de Nederlandse zeewieren. Natuurhistorische Bibliotheek van de KNNV, 33. Koninklijke Nederlandse Natuurhistorische Vereniging (KNNV): Hoogwoud. 263 pp. [http://www.vliz.be/imis/imis.php?module=ref&refid=11712]

VLIZ Alien Species Consortium (2020). Melanothamnus harveyi – Harvey's siphon weed. Non-native species of the Belgian part of the North Sea and adjacent estuaries anno 2020. Flemish Institute for the Sea (VLIZ). 5 pp.