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Morphotaxonomy, genetic affinities and ecology of Australian and Antarctic populations of the potentially fish killing, heterotrophic dinoflagellates Cryptoperidiniopsis brodyi and Pfiesteria piscicida

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Park, Tae-Gyu 2006 , 'Morphotaxonomy, genetic affinities and ecology of Australian and Antarctic populations of the potentially fish killing, heterotrophic dinoflagellates Cryptoperidiniopsis brodyi and Pfiesteria piscicida', PhD thesis, University of Tasmania.

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Abstract

The heterotrophic dinoflagellate Cryptoperidiniopsis brodyi and closely related
species were investigated from Australia-wide marine environments with regard to
their morphology, phylogenetic relationships, interactions with shellfish larvae, and
natural abundance. Nine isolates of C. brodyi and two isolates of Pfiesteria piscicida
were collected and cultured from Australia and ballast water originating from
Indonesia. Scanning electron microscopy (SEM) and molecular sequence analyses of
SSU, LSU, ITS, and 5.8S rDNA regions revealed that Australian C. brodyi strains
have identical morphological features but include two different genetic variants.
Isolates of C. brodyi from Australia, comprised the two ITS genotypes A and B which
diverged 16.2% and 6.6%, respectively, of the ITS genotype from the U.S. type
locality. Genotype A was widespread whereas genotype B thus far has only been
found in Tasmania. Pfiesteria piscicida was cultured from ballast water indicating a
potential inflow of foreign harmful algae into Australian waters. Previous studies
using PCR-based assays claimed a wide distribution of Pseudopfiesteria shumwayae
in Australia including in Brunswick River in Western Australia. However, isolates
from the Brunswick River samples were identified in the present work as C. brodyi.
Nonspecific reactions from P. shumwayae SSU rDNA-based primers were confirmed
with Australian C. brodyi. This suggests that P. shumwayae presence in Australia has
been overestimated by previous molecular detection methods.
A species-specific real-time PCR assay using the TaqMan® probe system was
developed for rapid detection and quantification of C. brodyi in environmental
samples. Specific PCR primer-probes for C. brodyi were designed against the ITS2
rDNA regions and tested for selectivity, specificity and sensitivity of detection. The
assay was able to detect the presence of less than 1 cell per PCR reaction, did not
respond to non-target species, and accurately quantified C. brodyi in natural water
samples. This assay was used together with previously reported P. piscicida- and P.
shumwayae-specific real-time PCR assays to investigate the temporal variation in C.
brodyi, P. piscicida, and P. shumwayae in the Derwent estuary, Tasmania from
November 2004 until April 2006. Cryptoperidiniopsis brodyi occurred throughout
the years at very low abundances (below 112 cells L-1), while P. piscicida was detected
only once and P. shumwayae was never detected during the 18 month survey (36
sampling dates). A further 8 cultures established from the Chapman River, Western
Australia, during September 2005 were also all confirmed as C. brodyi. The species
specific real-time assays were also used to examine Ace Lake water samples collected
from Antarctica. Pfiesteria piscicida cells were detected and confirmed by partial
DNA sequences of the PCR amplicons.
Feeding behaviour and interactions of C. brodyi and P. piscicida with Pacific
oyster (Crassostrea gigas) larvae and brine shrimp (Artemia salina) nauplii were
examined in a micro-scale bioassay format. The zoospores became active and showed
aggressive feeding response toward oyster larvae. Micropredation resulted in deaths
of planktonic oyster larvae (below Imm size), but zoospores were less attracted to
brine shrimp and no deaths of brine shrimp were observed. Given the very low
abundances of C. brodyi and P. piscicida in the Derwent estuary, adverse effects from
micropredatory feeding by these dinoflagellates on planktonic larvae may rarely occur
in this environment.
This study demonstrates the geographic and temporal variations in C. brodyi, P.
piscicida and P. shumwayae by using species-specific real-time PCR, microscopy and
sequence analyses. Continued studies of additional isolates and field samples over a
range of temporal and spatial scales would allow a better understanding of
phylogeographic and ecological aspects of C. brodyi, Pfiesteria and Pseudopfiesteria
species.

Item Type: Thesis - PhD
Authors/Creators:Park, Tae-Gyu
Keywords: Dinoflagellates, Dinoflagellates, Shellfish, Oysters
Copyright Holders: The Author
Copyright Information:

Copyright 2006 the author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
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Additional Information:

Available for library use only but NOT for copying until 30 September 2008. After that date, available for use in the Library and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2007. Includes bibliographical references

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