| Summary: | Typescript Thesis (PhD) -- University of Melbourne, Faculty of Science, 2006 Includes bibliographical references (leaves 178-189) The morphology of Antarctic krill, Euphausia superba, has traditionally been described using measures of size, such as total length, carapace length, and uropod length, or weight, or a combination of these. These measures are then used to derive other biological parameters such as growth rate, recruitment size, and biomass. Despite well- established protocols for deriving parameters from linear measurements, this practise can be problematic because krill can shrink. There is therefore a need to develop new methods that do not rely on length measurements for studying krill population structure and this thesis describes such work. Geometric morphometrics (GM) provides a possible alternative to using linear measurements for describing body morphology, and to date has not been used to study krill populations. One of the GM methods uses landmarks to capture the geometry of morphological structures independently of size and this allows size to be compared to shape, rather than shape being described using size measures. Differences in shape can then be described within- and between- groups of specimens. A series of freeware programs enable a trained operator to facilitate the shape analysis process. In this study, live and preserved krill specimens were gathered from various locations around Antarctica. The lateral aspect of the carapace was photographed and six landmarks were digitised to capture the geometry of the carapace. Traditional size variables were measured during the GM analysis so that the relative success of the GM method against existing methods could be reported. The specimens selected for the GM analysis were compared to the sampled population using the relationship between carapace length and total length for different maturity stages. This relationship was similar between female maturity stages, whereas male krill displayed carapace dimorphism between maturity stages. ...
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