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Ecology and ecophysiology of Katelysia scalarina (Bivalvia: Veneridae), a commercially exploited clam


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Bellchambers, LM 1998 , 'Ecology and ecophysiology of Katelysia scalarina (Bivalvia: Veneridae), a commercially exploited clam', PhD thesis, University of Tasmania.

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The general aim of this study was to increase knowledge of Katelysia scalarina an
intertidal suspension feeding bivalve common in many of the sheltered bays and
estuaries of southern Australia. Specifically, attention has been focused on the
factors that may determine the distribution and abundance of natural populations.
Secondly, information was gathered to help ensure effective management of
natural populations to prevent over-exploitation and provide a basis for future
aquaculture developments.
The effects of density and tidal level on the survival, growth and meat ratio of K.
scalarina were examined using a series of caged manipulation trials. Both density
(171.5-686.1 clams/m2) and tidal position had significant effects on the survival
and growth of K scalarina with a decrease in survival and growth evident with
increasing distance from the low tide mark. Shell growth at high tidal positions
was approximately half of that lower on the shore, which may be due to the
depletion of food resources. In contrast, meat ratio displayed a direct relationship
with tidal position, as a result of suppressed shell growth at high tidal positions.
In contrast to the above trial, the effects of stocking density were much smaller
than that of tidal level. None of the measured parameters displayed a significant
response to density manipulations of K scalarina grown at a single tidal position.
The failure of K scalarina to respond to density treatments up to thirty times that
of the natural population may in part be due to the location of the experimental
treatments. Experimental cages situated low in the intertidal zone may provide
suspension feeders access to a very abundant food source, negating the effects of
artificially enhanced densities.
The salinity tolerance of adult and juveniles was investigated using a series of acute
(21d) toxicity trials (5-550/oo). Results indicate that adults are intolerant of low salinities
(<250/00), while juveniles have a wide salinity tolerance range. Despite differences in
the salinity tolerance of adults and juveniles, there were no significant differences in
their ability to osmoregulate. K. scalarina is essentially an osmo- and ionic-conformer,
with the possible exception of r, that relies on the mechanism of shell valve closure to
isolate the body tissues from unfavourable salinities. Results indicate that K scalarina
relies on regulation of the free amino acid pool to cope with fluctuations in the external
medium. Although K scalarina is capable of surviving a salinity range of 25-500/oo, the
zone for optimal growth may be a narrower band within this range. Respiration
and algal clearance trials were conducted to determine whether irregular valve
closure patterns limit oxygen consumption and algal clearance which may in turn
limit growth potential. Oxygen consumption was depressed in salinities outside
350/0o even though these salinities were within the tolerance range. However,
evidence from algal clearance trails was not so clear cut. Juveniles display a
decrease in algal consumption in salinities > 45Voo and < 300/oo.
The potential for K. scalarina to be grown as a by-crop on existing oyster farms in
Tasmania promoted the investigation of the natural food sources of the species.
Besides using the existing infrastructure of established marine farms these areas
offer a number of additional food sources due to organic enrichment from
pseudofaeces and biodeposition. The stomach contents of clams situated both
below existing oyster racks and away from oyster racks indicated that K scalarina
is a suspension feeder that relies primarily on phytoplankton present in the water
column for nutrition. This indicates that potential exists for competition for food
resources if K scalarina is grown in oyster growing areas in southern Australia.
However, K scalarina exhibited poor survival in cages when grown on several
commercial oyster leases.
Despite commercial exploitation of K scalarina, this study is the first
comprehensive investigation of the species and therefore provides a valuable
resouce for the management of wild populations and future aquaculture ventures.
Finally, this study contributes significantly to the existing knowledge of a
dominant component of the southern Australian estuarine fauna.

Item Type: Thesis - PhD
Authors/Creators:Bellchambers, LM
Keywords: Clams
Copyright Holders: The Author
Copyright Information:

Copyright 1998 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:

Thesis (Ph.D)--University of Tasmania, 1999. Includes bibliographical references

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