Diseases, pathogens and parasites of Undaria pinnatifida

al. 2003; Hubbard et al. 2004). One of the potential threats of Undaria pinnatifida to New
Zealand native kelps may consist of competition with other kelp gametophytes as endophytes.
III: FUTURE STRATEGY FOR SCREENING POPULATIONS AND INCREASING
KNOWLEDGE OF RISK POSED BY DISEASES/PARASITES/PATHOGENS TO NEW
ZEALAND MACROALGAE AND COASTAL COMMUNITIES
None of the known pathogens of Undaria have so far been observed in/on U. pinnatifida in
New Zealand, however, populations of U. pinnatifida around New Zealand have not been
screened for the presence of diseases, pathogens and parasites. Given that there is evidence
that New Zealand has received at least 10 separate introduction events of Undaria pinnatifida
(Uwai et al. 2006), it would be important to construct a sampling regime that reflected this
known genetic diversity within New Zealand populations of Undaria.
Correa (1997) recommends an operational approach to the study of infectious diseases in
seaweeds:
1. field and laboratory observations aiming to individualize a potential pathogen and to
describe the lesions associated with the presence of that organism,
2. laboratory experiments and observations to establish causality i.e. applying Koch’s
postulates (Andrews & Goff 1984), as well as manipulative experiments to understand
aspects of the host-pathogen relationship and thus develop methods to manage the
disease, e.g. in marine cultures
3. epidemiology to “evaluate... the population segment ...affected..., the severity of the
disease and the occurrence of seasonal and spatial patterns of disease expression”, which
includes the study of the reproduction, mortality and physiological performance of the
host population and individuals.
From the research conducted by Heesch (2005) it is clear that it is necessary to identify host
populations and look for disease symptoms both intra- and inter-annually, with seasonal
sampling occurring ca. quarterly. Given the range of environments, water temperatures, and
photoperiods experienced through the New Zealand region, the sampling would need to be
stratified and targeted on priority taxa. Depending on the biology of the target taxa the
sampling regime would need to incorporate considerations of the species life history (i.e.
whether the species has isomorphic or heteromorphic alternation of generations or direct
development; if life history phases have differing cell wall chemistry as found for example in
isomorphic phases of members of the Gigartinales), ecology and distribution (light, depth,
exposure/shelter, substrate). Causality between disease and symptoms requires both field and
detailed laboratory investigations.
A number of authors point to the importance of considering diseases, pathogens and parasites
in the wider context, testing hypotheses about the roles they may play in shaping population
and community structure (Correa 1997; Prenter et al. 2004; Tompkins & Poulin 2006).
32 • Diseases, pathogens and parasites of Undaria pinnatifida MAF Biosecurity New Zealand