Diseases, pathogens and parasites of Undaria pinnatifida

Biological invasions are understood to pose a significant threat to biodiversity, and parasites
are considered to play a role in determining the outcomes of invasions. Transmission of
parasites to native species from the invading species can influence the fitness of native taxa,
mediating competitive interactions. Introduced diseases may have catastrophic impacts or
may result in persistent and sub-lethal effects on natives and consequent impacts on
community structure (Prenter et al. 2004). Introduced hosts may also play a role as reservoirs
for native diseases, pathogens and parasites from which potentially deleterious “spillback” of
infection to native hosts may occur (Prenter et al. 2004; Tompkins & Poulin 2006). Tompkins
& Poulin (2006) observe that although many parasites are apparently lost from hosts when
they are introduced to a new environment, the introduced hosts tend to acquire generalist
parasites from the native biota. Impacts of disease are often dependent on the context, with
multiple abiotic and biotic factors implicated in the emergence of parasites, invasion
processes, and the impacts experienced by native biota (Blaustein & Kiesecker 2002). Factors
which increase host susceptibility to infection, including a range of stressors such as habitat
alteration and degradation, may make them more prone to introduced parasites. Artificial
rearing and aquaculture increase the potential for disease transmission as well as increasing
potential host susceptibility in crowded or sub-optimal growth conditions. Correa (1997)
considers that long term strategies for disease control in macroalgal farms will only succeed if
the genetics of disease resistance in the host and virulence in the pathogen are understood.
The risks that diseases, pathogens and parasites of Undaria pose to the New Zealand marine
environment have yet to be quantified. To fully understand Undaria’s impacts and to
effectively implement control or management options, diseases, pathogens and parasites
associated with this species as well as with other macroalgae need to be documented, both
internationally and nationally.
In this study the status of known diseases, pathogens and parasites of Undaria was
determined (Objective 1) and literature was reviewed for reports of these diseases, pathogens
and parasites in Undaria populations in New Zealand (Objective 3). Diseases, pathogens and
parasites of other macroalgae known internationally were summarised (Objective 2), as was
information relating to those present in macroalgal populations in New Zealand (Objective 4).
Within a wider consideration of diseases, pathogens and parasites of macroalgae there are
difficulties in confirming a causal role of specific organisms that have been implicated in
disease or infection. The confirmation of Koch’s postulates is the exception rather than the rule.
Thus, the database developed in this proposal has considered all organisms that have been
associated with infection/disease/pathology with a clear indication of the evidence linking
specific organisms to disease states/symptomology.
4 • Diseases, pathogens and parasites of Undaria pinnatifida MAF Biosecurity New Zealand