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Abstract

The dinoflagellates Ostreopsis siamensis, Coolia monotis, Prorocentrum lima
and Prorocentrum rhathymum are commonly recognized as tropical, epiphytic species.
The present work reports the occurrence of this assemblage from temperate seagrass
habitat on the east coast of Tasmania, Australia. Molecular genetic sequencing, revealed
little variance (- 0.2 %) within 0. siamensis, P. lima and P. rhathymum strains and high
variance (-25%) within C. monotis strains where 3 major clades were seen, loosely
based on geographical distribution. All species exhibited growth at lower temperature
ranges (10-25 °C) than that described for tropical species (20-30°C). Ostreopsis
siamensis survived 10 °C in the form of a vegetative resting stage. We conclude that this
epiphytic assemblage is most likely indigenous to Tasmania, and not a recent range
extension from tropical Queensland.
Toxins were identified from all epiphytic species. Ostreopsis siamensis
contained 0.011-0.05 pg palytoxin ceir 1, C. monotis extracts (1.5x106 cells) caused death
in mice within 12 hrs, P. lima contained diarrhetic shellfish toxins (25 pg ceir 1 okadaic
acid and 2 pg celr 1 DTX-1) and uncharacterised fast acting toxins were found in P.
rhathymum extracts (1.8 x 107 cells) causing mouse death in 20 mins. Toxicity of P.
rhathymum was further investigated following recognition of an association between
seasonal oyster spat (Crassostrea gigas) mortalities and high (-12 OOO cells L" 1)
P. rhathymum density in a local estuary (Little Swanport). Oyster spat feeding assays
revealed histopathological symptoms similar to those seen in affected field samples
(thin, dilated gut tubules and sloughing of gut cells), however no mortality was
observed. In a comparable incident, an unprecedented mortality of farmed Sydney rock
oysters (Saccostrea glomerate) in New South Wales led to investigation of another
Prorocentrum species (P. minimum) as a possible causative agent. Brine shrimp and
intraperitoneal mouse bioassays were negative for toxic effects. However, oyster spat
bioassays evoked distinctive histopathological symptoms (large focal reactions in the
digestive tubules and gills). These findings add an entirely new dimension to
investigations into harmful Australian microalgae with implications for aquaculture not
in terms ofbiotoxin contamination, but as the cause of major shellfish mortalities.
The little known freshwater Prorocentrum, P. playfairi and P. foveolata, were
successfully cultured for the first time from Tasmanian coastal lagoons to elucidate their
possible toxicity, ecophysiology and genetic affinities with better-known marine
congeneric species. Prorocentrum playfairi only grew in salinities of 0-5 psu, whereas
P. foveolata tolerated salinities of 0-30 psu. Both species were negative for diarrhetic
shellfish toxins such as those found in marine Prorocentrum. Molecular sequencing
suggested that these species are good Prorocentrum but more closely related to toxic
benthic marine Prorocentrum (P. lima, P. cf. belizeanum ), than pelagic marine
Prorocentrum (P. gracile, P. triestinum, P. compressum etc.). We suggest a possible
evolutionary origin from P. lima like dinoflagellates through the isolation of coastal
lagoons and subsequent adaptation to freshwater.

Item Type:	Thesis - PhD
Authors/Creators:	Pearce, Imojen
Keywords:	Dinoflagellates, Dinoflagellates
Copyright Holders:	The Author
Copyright Information:	Copyright 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 would be pleased to hear from copyright owner(s).
Additional Information:	Thesis (Ph.D.)--University of Tasmania, 2004. Includes bibliographical references.
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