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Kelp forests in False Bay: urchins vs. macroalgae in South Africa's south-west coast biogeographical transition zone
There is ongoing global concern over unwanted regime shifts in marine systems. Shifts from diverse and productive algal-dominated ecosystems to less productive urchin and coralline-dominated temperate reefs are becoming increasingly common. Kelp forests found along South Africa's south-west coast be...
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| Format: | Thesis |
| Language: | English |
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Department of Biological Sciences
2017
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| _version_ | 1867613215145328640 |
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| access_status_str | Open Access |
| author | Morris, Kathryn |
| author2 | Blamey, Laura K |
| author_browse | Blamey, Laura K Morris, Kathryn |
| author_facet | Blamey, Laura K Morris, Kathryn |
| author_sort | Morris, Kathryn |
| collection | Thesis |
| description | There is ongoing global concern over unwanted regime shifts in marine systems. Shifts from diverse and productive algal-dominated ecosystems to less productive urchin and coralline-dominated temperate reefs are becoming increasingly common. Kelp forests found along South Africa's south-west coast between Cape Point and Cape Agulhas occur in a region of biogeographical overlap. They are commonly referred to as transition zone kelp forests and are dynamic ecosystems that are particularly susceptible to grazing influence from species such as sea urchins. This study (1) explores the uniformity of these transition zone kelp forests along the western side of False Bay, with a focus on macroalgae and urchins, (2) identifies a threshold in urchin density above which algal abundance declines and (3) seeks to identify relationships between attached and drift algal abundance. Twenty replicate quadrats were sampled in six kelp forests along the western side of False Bay. Within each quadrat, urchins (Parechinus angulosus) and kelps (Ecklonia maxima) were counted, percentage covers of various understorey algal species were recorded and drift algae were collected. Although there was significant variability in algal and urchin cover across the six sites, kelps generally increased from north to south, while urchins did the opposite. Urchins were negatively correlated with algal communities, and a localised threshold of 1.43kg/m² (50 urchins/m²) was identified, above which attached kelp density failed to increase above 10/m² and percentage cover of understorey algae usually remained below 20%. Surprisingly, no relationship was discovered between abundance of drift kelp and attached kelp, understorey algae or urchin density. This result was likely distorted by the naturally turbulent conditions of South African waters. Results highlight the complexity of these cool-water environments. To better understand the role of urchins in this system, experimental research into the feeding behaviour and effect of P. angulosus on kelps and understorey seaweeds in the presence/absence of drift algae is advised. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/25072 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:32:36.207Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2017 |
| publishDateRange | 2017 |
| publishDateSort | 2017 |
| publisher | Department of Biological Sciences |
| publisherStr | Department of Biological Sciences |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/25072 Kelp forests in False Bay: urchins vs. macroalgae in South Africa's south-west coast biogeographical transition zone Morris, Kathryn Blamey, Laura K Biological Sciences There is ongoing global concern over unwanted regime shifts in marine systems. Shifts from diverse and productive algal-dominated ecosystems to less productive urchin and coralline-dominated temperate reefs are becoming increasingly common. Kelp forests found along South Africa's south-west coast between Cape Point and Cape Agulhas occur in a region of biogeographical overlap. They are commonly referred to as transition zone kelp forests and are dynamic ecosystems that are particularly susceptible to grazing influence from species such as sea urchins. This study (1) explores the uniformity of these transition zone kelp forests along the western side of False Bay, with a focus on macroalgae and urchins, (2) identifies a threshold in urchin density above which algal abundance declines and (3) seeks to identify relationships between attached and drift algal abundance. Twenty replicate quadrats were sampled in six kelp forests along the western side of False Bay. Within each quadrat, urchins (Parechinus angulosus) and kelps (Ecklonia maxima) were counted, percentage covers of various understorey algal species were recorded and drift algae were collected. Although there was significant variability in algal and urchin cover across the six sites, kelps generally increased from north to south, while urchins did the opposite. Urchins were negatively correlated with algal communities, and a localised threshold of 1.43kg/m² (50 urchins/m²) was identified, above which attached kelp density failed to increase above 10/m² and percentage cover of understorey algae usually remained below 20%. Surprisingly, no relationship was discovered between abundance of drift kelp and attached kelp, understorey algae or urchin density. This result was likely distorted by the naturally turbulent conditions of South African waters. Results highlight the complexity of these cool-water environments. To better understand the role of urchins in this system, experimental research into the feeding behaviour and effect of P. angulosus on kelps and understorey seaweeds in the presence/absence of drift algae is advised. 2017-09-06T07:08:50Z 2017-09-06T07:08:50Z 2017 Master Thesis Masters MSc http://hdl.handle.net/11427/25072 eng application/pdf Department of Biological Sciences Faculty of Science University of Cape Town |
| spellingShingle | Biological Sciences Morris, Kathryn Kelp forests in False Bay: urchins vs. macroalgae in South Africa's south-west coast biogeographical transition zone |
| thesis_degree_str | Master's |
| title | Kelp forests in False Bay: urchins vs. macroalgae in South Africa's south-west coast biogeographical transition zone |
| title_full | Kelp forests in False Bay: urchins vs. macroalgae in South Africa's south-west coast biogeographical transition zone |
| title_fullStr | Kelp forests in False Bay: urchins vs. macroalgae in South Africa's south-west coast biogeographical transition zone |
| title_full_unstemmed | Kelp forests in False Bay: urchins vs. macroalgae in South Africa's south-west coast biogeographical transition zone |
| title_short | Kelp forests in False Bay: urchins vs. macroalgae in South Africa's south-west coast biogeographical transition zone |
| title_sort | kelp forests in false bay urchins vs macroalgae in south africa s south west coast biogeographical transition zone |
| topic | Biological Sciences |
| url | http://hdl.handle.net/11427/25072 |
| work_keys_str_mv | AT morriskathryn kelpforestsinfalsebayurchinsvsmacroalgaeinsouthafricassouthwestcoastbiogeographicaltransitionzone |