A Characterization of the Organism Known as Didymo. and What Makes It a Pest in New Zealand.

Didymosphenia geminata (Lyngbye) M. Schmidt (1899)5 otherwise known as Didymo, is an unwanted organism in New Zealand8.   It has been causing significant invasive blooms in New Zealand’s South Island Rivers and streams since its initial discovery in 2004. Its bloom of large slimy mat like structures made of copious amounts of extracellular stalk, can coat the river floors with a benthic mat of siliceous slime, coating the riverbeds stones, and causing an eyesore to our highly valued, picturesque rivers. It competes in the same ecosystem as our native periphyton but the question is, what characteristics, compared with other members of the same taxonomic group, make Didymo a pest in New Zealand.   The unwanted invasive algae was first spotted during a routine periphyton inspection of the Waiau river in Southland late October 20044.   Despite large scale attempts to restrict its spread through national awareness and decontamination programs, it has since spread far and wide over the South island. Its rapid spread is very disheartening, especially for the people that use the rivers for recreation whether that be for fishing, boating, or swimming. These recreational pursuits have all been involved in containment attempts through vigorous cleaning regimes and restrictions of movements between waterways, but in vain.   It would seem that this unwanted algae is very difficult to eliminate6.
Didymosphenia geminata is a microscopic unicellular algae called a diatom (Bacillariophyta).   Diatoms are unique for their distinctive siliceous cell walls, which make them very hardy. D. geminata, a Pennate diatom1 (bilaterally symmetrical), often possess a raphe system which consist of slits along the valve of the cell that secrete a mucous for motility and, sometimes stalk growth. In the case of didymo, apical pore fields also allow the secretion of mucilage pads and stalks.   As I will discuss later, these stalks and the large cell structure compared to other species amongst the... [continues]

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