Polysiphonia brodiei

Other Scientific Names

• Ceramium brodiei (Dillwyn) C.Agardh, 1811
• Conferva brodiei Dillwyn, 1809
• Hutchinsia brodiei (Dillwyn) Lyngbye, 1819
• Hutchinsia penicillata C.Agardh, 1828
• Polysiphonia brodiei f. densa Holmes & Batters, 1890
• Polysiphonia penicillata (C.Agardh) Sprengel, 1827

Local Common Names

• Denmark: knippeledtang
• Norway: penseldokke

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Rhodophyta
•             Class: Rhodophyceae
•                 Order: Ceramiales
•                     Family: Rhodomelaceae
•                         Genus: Polysiphonia
•                             Species: Polysiphonia brodiei

Polysiphonia brodiei (Dillwyn) Spreng. is a red alga belonging to the family Rhodomelaceae within the order Ceramiales (Rhodophyta). The specific name, recognizing the Scottish botanist James Brodie, was initially and incorrectly spelt “brodiaei”. Silva et al. (1996) noted that in forming the epithet the genitive inflection should be added to the unmodified name in accordance with Rec. 60C.3 of the International Code of Botanical Nomenclature.

The type locality is Bantry Bay, Cork, Ireland (Womersley, 1979: 497). The type specimen is Lectotype BM-K; Probable Syntype: LD – 24.vi.1807, Hutchins. (Maggs and Hommersand, 1993). The basionym is Conferva brodiaei Dillwyn 1809: 81, pl.107, and recorded synonyms include: Ceramium brodiaei (Dillwyn) C.Agardh; Hutchinsia brodiaei (Dillwyn) Lyngbye; Hutchinsia penicillata C.Agardh; and Polysiphonia penicillata (C.Agardh) Spreng.

Species of Polysiphonia are generally distinguished by the number of pericentral cells present (ranging from 4 to 12 or more), the degree of cortication of the axes, the growth habit and robustness of plants, as well as on the basis of particular features of vegetative and reproductive cells e.g. presence/absence of trichoblasts, shape of the cystocarp, size and shape of spermatangial branches (e.g. Womersley, 1979).

P. brodiei is a red alga, generally 5-25 cm in height although they may be as tall as 40 cm, dark reddish brown to crimson purple in colour, and profusely and irregularly branched. The plants are attached to the substrate by numerous rhizoids and a mat of interwoven, branched prostrate axes that develop from the base of young axes. The axes are extremely soft and flaccid when young, becoming firmer and flexible when older. There are several main percurrent axes that are generally 0.6-0.9 mm in diameter, and which bear numerous, spirally arranged laterals. The lower axes are heavily corticated by several layers of small cells. Only the new growth of the upper axes are ecorticate, with well-defined segments visible. There are (6)7-8 pericentral cells. Trichoblasts or scar cells are on every segment, and the trichoblasts are slender and 2-4 times furcate. Branches are formed in the axils of the trichoblasts. Plants are dioecious.

Cystocarps have short stalks, and are urceolate with the ostiolar cells slightly inflated. The spermatangial branches develop as a branch of a trichoblast, and are cylindrical with a rounded to pointed apex. Tetrasporangia are formed in long spiral series, with a divergence of 1/6 to 1/7. When mature, the tetrasporangia occupy about half the segment width resulting in a slight distortion of the segments. Maggs and Hommersand (1993) noted that the morphology of this species varies greatly with environmental conditions. Plants found on lower intertidal shores or floating structures are elongate and flaccid with a cylindrical outline to the laterals, whereas in upper shore pools the plants are densely tufted and have a pyramidal outline.
 

P. brodiei was first reported in Australia in 1979 as a species that had probably been introduced via shipping (Womersley, 1979), based on specimens collected from 1940 onwards. In New Zealand P. brodiei was reported for the first time by Adams (1983) based on a specimen collected in 1940 from Wellington Harbour, (North Island). This species has been subsequently reported from sites in the North, South and Stewart Islands, primarily in busy ports growing on harbour structures (Adams, 1991; Nelson, 1999). However, the record of Harvey (1855:230) of Conferva brodiaei Dillwyn from Port Pegasus, Stewart Island, New Zealand, was incorrect and based on material of P. muelleriana. J.Agardh (Adams, 1991:423).

It appears to increasing in abundance even in its native range. In a study comparing the macroalgal vegetation of the Swedish Skagerrak coast in 1960-61 with the flora present in 1997, it was found that P. brodiei increased in abundance, and this was considered to be a response to increased eutrophication at the study sites (Johansson et al., 1998).

It may be considered possible, if not likely, that P. brodiei is spread at least locally by tides and currents.

There are no recorded instances of spread via biotic agents.

P. brodiei is considered to have been introduced to Australia, New Zealand, North America and Japan through shipping/vessel movements. As a small filamentous species, with a broad natural distribution range both geographically and ecologically, as well as the capacity to grow on a wide range of substrata, P. brodiei is an “ideal” fouling species. This species can be distributed long distances through vessel-hull fouling involving large and small commercial vessels as well as recreational craft. In addition this species can be translocated shorter distances via vessels as well as contaminated marine equipment, e.g. ropes, pontoons and marine farming equipment.

There is no known example of intentional introduction of this species.

In a study conducted in Australia to identify and rank introduced marine species found within Australian waters, P. brodiei was considered to be a “medium priority species” based on its invasion potential from infected to uninfected bioregions. Based on its impact potential, both economic and environmental, P. brodiei was identified as one of the 10 most damaging potential domestic target species in Australia (Hayes et al., 2005). However, the nature of the impacts caused by P. brodiei are not clear. P. brodiei may have impacts on the settlement of other marine species as it may be able to colonise surfaces more effectively/competitively than native species. There is no information on either the palatability of this species or its nutritional value for grazers, relative to other equivalent filamentous/turfing red algae.

• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Highly adaptable to different environments
• Is a habitat generalist
• Has high reproductive potential

• Modification of natural benthic communities
• Negatively impacts aquaculture/fisheries
• Reduced amenity values

• Competition - shading
• Competition - smothering
• Competition (unspecified)
• Fouling

• Highly likely to be transported internationally accidentally
• Difficult to identify/detect in the field