Thesis
Kelp gametophytes in a changing ocean: Ecklonia radiata microscopic stages and their role in resilience to climate change
Southern Cross University
Doctor of Philosophy (PhD), Southern Cross University
2023
DOI:
https://doi.org/10.25918/thesis.292
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Abstract
Kelp forests underpin temperate coastlines globally but are declining due to ocean change. To understand effects of ocean change on kelp forests, knowledge on the full life cycle is vital. Kelps alternate between diploid adult sporophytes and haploid microscopic gametophytes. Compared to sporophytes, relatively little is known on gametophytes’ role in the overall resilience of kelp forests to ocean change. In this thesis, aspects of kelps microscopic life stage are studied in the context of ocean change through both field and lab studies, using the main canopy forming kelp of Australia, Ecklonia radiata. A comprehensive literature review (Chapter 2) revealed knowledge gaps pertaining to exact timing of transitions between sporophyte and gametophyte, population specific adaptation, as well as ecological interactions of gametophytes. Chapter 3 found that the transition from sporophyte to gametophyte through release of haploid spores is adapted to local environmental conditions in E. radiata. Spore release was dependent on temperature in cooler, higher latitude populations, while in the warm-adapted population spore release related to stochastic events such as storms. Overall, spore release is not likely to be hampered by future ocean change. Chapter 4 revealed local adaptation is present in the gametophyte stage, and population-specific thermal tolerances were found to be 2-3°C higher than maximum in situ temperatures. Population-specific projections to a 2050 future under RCP8.5 revealed E. radiata gametophytes are likely to be resilient to future ocean warming, with minimal changes (0-30%) in survival throughout its eastern Australian range. However, ocean warming is not the only threat to kelp persistence. Replacement by fast growing turfing algae, as well as overgrazing by urchins contribute to kelp decline. The role of gametophytes in these ecological interactions remains unresolved. Chapter 5 and 6 showed that grazers present in turf algae, as well as juvenile urchins can reduce gametophyte abundance. However, they also facilitated recruitment into sporophytes through ingestion, though not under simulated ocean warming (26°C). This novel interaction indicates there may be a larger role for small grazers in kelp persistence than previously thought. Gametophyte recruitment following ingestion was not facilitated by the range-expanding urchin Centrostephanus rodgersii. This indicates a possible pathway in which C. rodgersii surpresses recruitment of E. radiata. While stage transitions to sporophytes may require certain conditions, including presence of small grazers and winter temperatures, gametophytes of E. radiata are overall likely resilient to ocean change and do not present a bottleneck for kelp forest persistence.
Details
- Title
- Kelp gametophytes in a changing ocean: Ecklonia radiata microscopic stages and their role in resilience to climate change
- Creators
- Rienje J. Veenhof
- Contributors
- Symon Dworjanyn (Supervisor) - Southern Cross UniversityMelinda Coleman (Supervisor) - Southern Cross UniversityCurtis Champion (Supervisor) - Southern Cross University
- Awarding Institution
- Southern Cross University; Doctor of Philosophy (PhD)
- Theses
- Doctor of Philosophy (PhD), Southern Cross University
- Publisher
- Southern Cross University
- Number of pages
- xvii, 229
- Identifiers
- 991013135513802368
- Copyright
- © RJ Veenhof 2023
- Academic Unit
- Faculty of Science and Engineering
- Resource Type
- Thesis