Diseases, pathogens and parasites of Undaria pinnatifida

identification. Often, they are not fertile when observed, making the correct identification
difficult.
Host symptoms are not always a good character for identifying pathogens/ parasites either, as
these may depend on the susceptibility of a host species to a specific agent. Susceptibility can
vary between generations of the same host species e.g. the sporophyte of the red alga
Chondrus crispus is susceptible to infections of the green endophyte Acrochaete operculata,
while the host gametophyte shows some resistance (Correa & McLachlan 1991). Life stages
of pathogens may also display different morphologies e.g. nauplii of harpacticoid copepoda
burrowing in kelp stipes may have to be reared to adult stages in order to correctly identify
them by morphology. Most references describe a disease by the symptoms expressed in the
host, but fall short of demonstrating causality, meaning for example, more obvious secondary
invaders could be mistakenly attributed as the primary cause of a disease. There is almost no
work that has examined more complex pathogen/host systems.
Information on diseases, pathogens and parasites occurring in New Zealand is scant.
Generally the publications available reflect the activities of a few overseas workers who have
visited or received specimens and have published on particular agents (e.g. Kohlmeyer).
There have been no focused studies incorporating field and laboratory investigations other
than the work of Heesch (2005) on endophytes of brown algae in New Zealand, completed as
research for a Ph.D. at the University of Otago.
II: ASSESSMENT OF THREATS BY PATHOGENS OF UNDARIA TO NEW ZEALAND
NATIVE MARINE FLORA
The only disease reported in Undaria from its introduced range is the infection of thalli with
the pigmented endophytic brown alga Laminariocolax aecidioides, both in Spain (Veiga et al.
1997) and in Argentina (Gauna et al. personal communication). It is not clear whether this
endophyte originates from Japanese populations introduced with the host or from European or
Argentinian populations respectively. Laminariocolax aecidioides is known from other,
native European kelps such as Laminaria hyperborea in the German Bight and Norway, and
Saccharina latissima in the Western Baltic Sea (Lein et al. 1991; Ellerstdottir & Peters 1995,
1997; Peters & Schaffelke 1996), but it has not been reported from southern Europe. It also
occurs in the native range of U. pinnatifida, in Japan (Yoshida & Akiyama 1978). Genetic
studies may determine the origin of the Spanish and Argentinean populations and thus shed
some light on whether endophytes were or can be transmitted with host sporophytes (or other
disease agents).
In the Western Baltic, thalli of Saccharina latissima infected with Laminariocolax aecidioides
show more severe symptoms in shallow water, due to the endophyte growth being accelerated
in better light conditions. Increased severity of infection symptoms prevent host thalli
surviving in water depths of 2 m, in contrast to deeper water where growth of the endophyte is
light limited (Schaffelke et al. 1996). In New Zealand, Laminariocolax macrocystis, a closely
related species in this genus, infects native kelps, such as Macrocystis pyrifera and Ecklonia
radiata, and in severe cases this leads to crippled thalli (M. pyrifera) and/or stunted growth
(E. radiata) (Heesch 2005). It is not known if this endophyte species has an influence on the
depth distribution of its hosts. Further, it is not known if L. aecidioides would be able to infect
New Zealand native kelps, and if so, what the consequences would be for native kelp
populations.
Reports in the international literature have highlighted the occurrence of kelp gametophytes as
endophytes in a range of hosts (e.g. Garbary et al. 1999a, b; Garbary & Kim 2000; Sasaki et
MAF Biosecurity New Zealand Diseases, pathogens and parasites of Undaria pinnatifida • 31