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Ecology of moon jellyfish Aurelia Sp. in southern Tasmania in relation to Atlantic salmon farming

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Willcox, ST (2006) Ecology of moon jellyfish Aurelia Sp. in southern Tasmania in relation to Atlantic salmon farming. PhD thesis, University of Tasmania.

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Abstract

The pattern of occurrence of medusae blooms in south east
Tasmania was linked to both local and global scale environmental
conditions. On average, summer water temperature was over one degree
warmer, local autumn rainfall was less than half, winter salinity was
0.7%o lower, and Southern Oscillation Index (SOI) values in winter,
spring, and summer were 10 - 12 points higher (and positive) in years
where blooms occurred compared to those where they did not. The
amount of local rainfall in autumn and the mean SOI value in winter
were identified as the most useful environmental variables for predicting
which summers will have medusae blooms.
Blooming Aurelia sp. medusae were studied in the Huon Estuary
from early December 2002 to late January 2003. Medusae grew
exponentially and reached a maximum mean diameter of over 150mm in
two months. Maximum mean growth rates of 7.3% body weight day-1
were measured before the pattern of growth broke and all medusae
disappeared at the end of January. The total number of medusae in the
Huon Estuary was estimated to be 169 million, with a total biomass of
over 28 000 tons prior to the population senescing.
Medusae formed into dense aggregations with densities up to 270
individuals m-3. Aggregations occurred in an environment with strong
horizontal current sheer where surface and bottom waters often flowed in
opposing directions and had velocities as high as 105 mm sec-1, yet were
able to maintain their integrity. Observations with underwater cameras and by SCUBA diving revealed a complex structure with coordinated
swimming of individuals within aggregations responsible for aggregation
maintenance.
Scyphistomae colony dynamics were examined in situ in south east
Tasmania. Colonies were perennial and persisted for at least three years.
Strobilation was observed every year in spring, however subsequent
blooms of medusae did not always develop. The density of scyphistomae
in colonies was a function of both the proportion of the substrate covered
by the colony and the density of individuals within discreet colony
patches. These variables were negatively correlated with competition
from other encrusting organisms and local rainfall, and positively
correlated with water temperature.
Laboratory experiments showed that temperature and salinity
affected rates of asexual reproduction. These factors resulted in
numerical increases in colonies up to 150% over a 32 day period. These
experiments also showed there is a trade off between increasing
population size through budding at high temperatures, and increasing
body size, possibly in preparation for strobilation, at low temperatures.

Item Type: Thesis (PhD)
Keywords: Jellyfishes, Atlantic salmon fisheries
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 would be pleased to hear from the copyright owner(s).

Additional Information:

Available for library use only and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2006. Includes bibliographical references

Date Deposited: 04 Feb 2015 23:32
Last Modified: 11 Mar 2016 05:54
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