Polysiphonia brodiei is a dark reddish brown macroalga, typically 4 to 12cm in height, but occasionally reaching 40cm. Many soft, filamentous branches arise from one or several main stems which grow from a holdfast of numerous small rhizoids. Delicate forked hairs (trichoblasts) are abundant and present on each branch. Tetrasporangia (reproductive structures) are round to oval in shape and are spirally arranged in the ends of the upper branches of the tetrasporophyte. Spermatangia (reproductive structures) develop from one branch of a trichoblast on male plants. Stalked cystocarps (reproductive structures) are round to oval in shape and are present on female plants (NIMPIS 2002).

There are no known consumers of P. brodiei, but fish, crabs and small crustaceans are known to feed on other Polysiphonia spp. (NIMPIS 2002). It has been discovered that the growth of the sporelings (young individuals developed from spores) of P. brodiei can be markedly influenced by coumarin, a common compound found in plants (Boney 1967).

Polysiphonia brodiei has a complicated three-stage life cycle. The macroscopic tetrasporophyte plant bears many tetrasporangia . These each release 4 microscopic spores that settle to form macroscopic male and female gametophyte plants. Male gametes are called spermatia (plural) or spermatium (singular) – fusion with the carpogonia (reproductive structures of the female plant) takes place via a trichogyne – hair like receptive surface. The resultant zygote develops into a cystocarp (borne on the female plant) that produces and releases carpospores which settle and develop into tetrasporophyte plants (Wendy Nelson., pers.comm., 2007; NIMPIS 2002).

Polysiphonia brodiei is usually found in the subtidal zone just below low tide level. This species colonises wooden structures such as jetties and pylons, floating structures such as ropes, buoys and vessels and other species such as mussels Mytilus edulis. P. brodiei seems to prefer moderately exposed localities. In Australia, New Zealand and California, specimens have been mostly collected from port environments (NIMPIS 2002).

In Victoria (Australia) and Newfoundland (Canada) P. brodiei reproduces in summer (NIMPIS 2002).

Polysiphonia brodiei is a primary producer or an autotroph. It creates its own food by fixing carbon through photosynthesis (NIMPIS 2002).

In California and New Zealand Polysiphonia brodiei is frequently found as hull fouling organism on slow moving vessels, such as barges. It is also fouls ropes and buoys and harbour structures such as pylons and boat ramps (NIMPIS 2002).

Preventative measures: A two year study was undertaken for the Department of Environment and Heritage (Australia) by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) to identify and rank introduced marine species found within Australian waters and those not found within Australian waters.
All of the non-native potential target species identified in this report are ranked as high, medium and low priority, based on their invasion potential and impact potential. Polysiphonia brodiei is identified as one of ten most damaging potential domestic target species, based on overall impact potential (economic and environmental). A hazard ranking of potential domestic target species based on invasion potential from infected to uninfected bioregions identifies P. brodiei as a 'medium priority species' - these species have a reasonably high impact/or invasion potential.
For more details, please see Hayes et al. 2005.
The rankings determined in Hayes et al. 2005 will be used by the National Introduced Marine Pest Coordinating Group in Australia to assist in the development of national control plans which could include options for control, eradication and/or long term management.