- Title
- Morphological and genetic analysis of the green alga Caulerpa taxifolia (Vahl) C. Agardh (Bryopsidales) in New South Wales, Australia.
- Creator
- Bohórquez Rueda, Carlos Alberto
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2013
- Description
- Masters Research - Master of Science (M.Sc)
- Description
- Caulerpa taxifolia (Vahl) C. Agardh (Bryopsidales) is a very common green marine alga in tropical waters of the world, including northern Australia. It is also found in subtropical Australian waters and in temperate shallow sea waters, usually in the protected estuaries and bays of New South Wales (NSW) and South Australia (SA), where it was recorded for the first time in 2000. C. taxifolia has been one of the top seaweed invaders in the Mediterranean Sea during the last decade, and for this reason its presence in temperate environments in South east Australia, outside its acknowledged natural range, is considered as an environmental threat. During the last decade, plans for its control, monitoring and risk assessment have been developed in both NSW and SA. Extensive research by universities and other scientific and management institutions has been conducted on a wide range of aspects of biology and management. Previous studies have usually focused on some specific aspect, such as morphology or genetics, using a range of techniques. The results however, are complex and contradictory and the question of the origin and identity of C. taxifolia strains in South Eastern Australia has not been resolved. The connections and sources of C. taxifolia populations in NSW estuaries still are not clearly understood and require integrating both morphological and genetic analysis. This study established morphological differences in C. taxifolia from different estuarine locations of New South Wales, set up experiments in the laboratory to study short-term morphological responses to different irradiances and completed a genetic analysis, using microsatellites, to identify genetic differences among populations. A large number of morphological characters (21) were recorded in this study, but only 11 showed no correlation and thus were selected to be used in the analysis. The morphology of C. taxifolia in NSW showed remarkable variability. Significant morphological differences were detected among populations in the estuaries, which varied according to the morphological character. At spatial scales greater than 100 km, significant variability was only detected in stolon diameter, ratio between fronds and rhizoids and, in distance between rhizoids (with the exception in one population). C. taxifolia in the estuarine locations in Southern New South Wales has morphology characterised by large and compacted thallus, while in Metropolitan Sydney the thallus is small, branched and slightly compacted. Based on overall morphology, a separation of two distinct geographical areas emerged, named the embayments and estuaries around Sydney (referred to as Metropolitan Sydney Area) and the coastal lakes in the south of the state (referred to as Southern NSW). In addition, the populations in Metropolitan Sydney were more similar to each other, than the populations within Southern NSW. In this area morphological characters showed a wider range of variability than those observed within Metropolitan Sydney. The more stable morphological characters, with the low coefficient of variation, were rachis width and distance between pinnules. The most variable was third frond followed by stipe length, frond length without stipe, distance between rhizoids and ratio between number of fronds and number of rhizoids. Southern NSW had higher mean values for 9 of 11 morphological characters compared to Metropolitan Sydney. The Metropolitan Sydney area has a typical marine environment while the Southern NSW is more variable environment (typical brackish). There were significant differences in irradiance and salinity, but no differences in temperature, dissolved oxygen and total nitrogen. A significant correlation was found between the environmental factor irradiance and stolon diameter, frond distance and rhizoid distance; between salinity and frond distance; and between dissolved oxygen and frond length without stipe. Analysis of all environmental variables showed that estuaries in geographical proximity had similar environmental characteristics (except Lake Conjola and Gunnamatta Bay). In the laboratory experiment, C. taxifolia exhibited a short-time morphological response to different irradiances, and it was not uniform for all morphological characters. After 31 days, in laboratory conditions, a significant difference was found in the response to irradiance treatments in six morphological characters: stolon diameter, pinnule length, rhizoid length, stipe length, distance between fronds and ratio between numbers of fronds and rhizoids. The other morphological characters (frond length without stipe, distance between pinnules, rachis width and distance between rhizoids) were similar under the different irradiance treatments. Distance between fronds was the only morphological character that was longer in the experimental algae than in the algae sampled in the field. The results of this experiment were consistent with the hypothesis that the response of the morphological characters (stolon diameter, ratio between numbers of fronds and rhizoids and distance between rhizoids) to different irradiances was limit within a certain range, similar to range found in the field for the populations in the same area (Metropolitan Sydney), and smaller compared to the range of values for the populations in the other area (Southern NSW). Genetic analysis based on seven microsatellite loci of the population of C. taxifolia in NSW, showed the presence of two clusters geographically linked. These are Metropolitan Sydney Area and Southern NSW. This clustering pattern was consistent with the differences found in the morphological analysis. Historical evidence of the invasion of C. taxifolia also indicates two centres of spreading out: Lake Conjola and Pittwater. These two historical dispersion centres match with the genetic clusters identified in this study. A high level of coincidence emerged in an integrative examination of the clustering pattern of geographic, morphology and genetic distances, among the different populations of C. taxifolia in NSW. This examination enables this study to conclude that there are two populations, differentiated morphologically and genetically, one in the Metropolitan Sydney and the other in Southern NSW.
- Subject
- Caulerpa taxifolia; morphology; environmental variables; genetics; NSW
- Identifier
- http://hdl.handle.net/1959.13/1043132
- Identifier
- uon:14169
- Rights
- Copyright 2013 Carlos Alberto Bohórquez Rueda
- Language
- eng
- Full Text
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