Developing sustainable seaweed aquaculture of the native kelp Ecklonia radiata in New Zealand
Permanent link to Research Commons versionhttps://hdl.handle.net/10289/15928
The native kelp Ecklonia radiata is a target species for seaweed aquaculture in New Zealand because of its broad distribution and desirable biomass profile (e.g., alginate, fucoidan, and phlorotannins). However, commercial farming practices for E. radiata are not yet developed. The objective of this thesis was therefore to create foundations for sustainable seaweed aquaculture of E. radiata in New Zealand by filling key knowledge gaps regarding patterns of genetic structure (Chapter 2), spatial and temporal variation in biomass composition (Chapter 3), the development of high-throughput methods for biomass grading (Chapter 4), and marine farm design (Chapter 5). The development of specialised cultivars is central for optimising key commercial traits for seaweed aquaculture; however, the introduction of genotypes from significantly different genetic sub-populations can reduce genetic diversity and genetic structure of wild populations. Analysis of molecular variance in populations of E. radiata in the North Island of New Zealand revealed significant differences at all three hierarchical levels of genetic structure that were analysed. The highest regional differentiation occurred between Wellington and other regions and was supported by Bayesian and redundancy models showing a high degree of genetic clustering among regions. Furthermore, pairwise Fₛₜ (genetic differentiation) revealed significant differences between most sites showing strong genetic structure and low connectivity also at a local level. These findings indicate that cultivars of E. radiata should not be translocated outside their area of origin, to prevent introducing genotypes from significantly different genetic sub-populations to wild sub-populations. Most analysed biomass components of E. radiata showed high spatial variation between sites, including alginate, glucose, and phlorotannins. However, there was no clear pattern in biomass composition among regions, indicating that these differences in biomass content are unlikely to be caused by genetic differences (i.e., Wellington samples did not stand out). Conversely, a strong seasonal pattern was detected with significant temporal variation detected for half of the quantified components. These results indicate that environmental variation is a key driver for the biomass composition of E. radiata and that the high spatial variation was due to do site-specific environmental conditions. In general, the biomass composition of E. radiata was comparable to that of commercially grown northern hemisphere species and could be a suitable southern hemisphere alternative for a wide range of commercial applications. The large spatial and temporal variation in biomass composition creates a need for high-throughput grading of raw biomass. Highly accurate models were built for estimating biomass concentration of glucose, alginate, phlorotannins, and carbon using mid-infrared (MIR) and near-infrared (NIR) spectroscopy. NIR models generally demonstrated higher accuracy and lower sensitivity to outliers than MIR models. Furthermore, samples from the Wellington region could consistently be identified based on the NIR data, demonstrating strong phenotypic differences between regions. These results show that NIR and MIR are valuable tools for high-throughput grading of raw seaweed biomass samples and can be used to establish provenance. Finally, farming trials quantified the effect of vertical and horizontal line configurations and farming depth on survival and growth of E. radiata at a commercial New Zealand green-lipped mussel (Perna canaliculus) marine farm. Only seaweed growing on vertical lines survived four months after deployment, and juvenile growth by elongation and maximum average individual weight was markedly higher on vertical lines compared to horizontal lines. Survival rates on vertical lines decreased at shallow depths, likely influenced by a combination of light and temperature stress. Similarly, the overall high mortality observed during the experiment was likely correlated to the prolonged marine heatwave of the summer of 2021/22 at the farm location. Conclusively, these results support vertical lines rather than horizontal line for farming of E. radiata. In summary, this thesis has significant scientific implications for regulatory (i.e., cultivar translocation), commercial (i.e., harvesting timing, biomass grading, and source tracing), and practical farming aspects (i.e., line configuration and a first proof on concept) of aquaculture of E. radiata in New Zealand and provides directions for future research and development.
The University of Waikato
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