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Veenhof RJ, Champion C, Dworjanyn SA, Schwoerbel J, Visch W, Coleman MA. Projecting kelp (Ecklonia radiata) gametophyte thermal adaptation and persistence under climate change. ANNALS OF BOTANY 2024; 133:153-168. [PMID: 37665952 PMCID: PMC10921825 DOI: 10.1093/aob/mcad132] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Accepted: 09/01/2023] [Indexed: 09/06/2023]
Abstract
BACKGROUND AND AIMS Kelp forests underpin temperate marine ecosystems but are declining due to ocean warming, causing loss of associated ecosystem services. Projections suggest significant future decline but often only consider the persistence of adult sporophytes. Kelps have a biphasic life cycle, and the haploid gametophyte can be more thermally tolerant than the sporophyte. Therefore, projections may be altered when considering the thermal tolerance of gametophytes. METHODS We undertook thermal tolerance experiments to quantify the effect of temperature on gametophyte survival, relative growth rate (RGR) and sex ratio for three genetically distinct populations of Ecklonia radiata gametophytes from comparatively high, mid- and low latitudes (43°, 33° and 30°S). We then used these data to project the likely consequences of climate-induced thermal change on gametophyte persistence and performance across its eastern Australian range, using generalized additive and linear models. KEY RESULTS All populations were adapted to local temperatures and their thermal maximum was 2-3 °C above current maximum in situ temperatures. The lowest latitude population was most thermally tolerant (~70 % survival up to 27 °C), while survival and RGR decreased beyond 25.5 and 20.5 °C for the mid- and low-latitude populations, respectively. Sex ratios were skewed towards females with increased temperature in the low- and high-latitude populations. Spatially explicit model projections under future ocean warming (2050-centred) revealed a minimal decline in survival (0-30 %) across populations, relative to present-day predictions. RGRs were also projected to decline minimally (0-2 % d-1). CONCLUSIONS Our results contrast with projections for the sporophyte stage of E. radiata, which suggest a 257-km range contraction concurrent with loss of the low-latitude population by 2100. Thermal adaptation in E. radiata gametophytes suggests this life stage is likely resilient to future ocean warming and is unlikely to be a bottleneck for the future persistence of kelp.
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Affiliation(s)
- R J Veenhof
- National Marine Science Centre, Faculty of Science and Engineering, Southern Cross University, Coffs Harbour, NSW, Australia
| | - C Champion
- National Marine Science Centre, Faculty of Science and Engineering, Southern Cross University, Coffs Harbour, NSW, Australia
- Fisheries Research, NSW Department of Primary Industries, National Marine Science Centre, Coffs Harbour, NSW, Australia
| | - S A Dworjanyn
- National Marine Science Centre, Faculty of Science and Engineering, Southern Cross University, Coffs Harbour, NSW, Australia
| | - J Schwoerbel
- Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
| | - W Visch
- Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
| | - M A Coleman
- National Marine Science Centre, Faculty of Science and Engineering, Southern Cross University, Coffs Harbour, NSW, Australia
- Fisheries Research, NSW Department of Primary Industries, National Marine Science Centre, Coffs Harbour, NSW, Australia
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Schwoerbel J, Visch W, Wright JT, Bellgrove A, Sanderson JC, Hurd CL. Thermal performance curves identify seasonal and site-specific variation in the development of Ecklonia radiata (Phaeophyceae) gametophytes and sporophytes. JOURNAL OF PHYCOLOGY 2024; 60:83-101. [PMID: 37897074 DOI: 10.1111/jpy.13406] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2023] [Revised: 08/25/2023] [Accepted: 09/26/2023] [Indexed: 10/29/2023]
Abstract
Rapid ocean warming is affecting kelp forests globally. While the sporophyte life stage has been well studied for many species, the microscopic life stages of laminarian kelps have been understudied, particularly regarding spatial and temporal variations in thermal tolerance and their interaction. We investigated the thermal tolerance of growth, survival, development, and fertilization of Ecklonia radiata gametophytes, derived from zoospores sampled from two sites in Tasmania, Australia, throughout a year, over a temperature gradient (3-30°C). For growth we found a relatively stable thermal optimum at ~20.5°C and stable thermal maxima (25.3-27.7°C). The magnitude of growth was highly variable and depended on season and site, with no consistent spatial pattern for growth and gametophyte size. Survival also had a relatively stable thermal optimum of ~17°C, 3°C below the optimum for growth. Gametophytes grew to single cells between 5 and 25°C, but sporophytes were only observed between 10 and 20°C, indicating reproductive failure outside this range. The results reveal complex effects of source population and season of collection on gametophyte performance in E. radiata, with implications when comparing results from material collected at different localities and times. In Tasmania, gametophytes grow considerably below the estimated thermal maxima and thermal optima that are currently only reached during summer heatwaves, whereas optima for survival (~17°C) are frequently reached and surpassed during heatwaves, which may affect the persistence and recruitment of E. radiata in a warmer climate.
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Affiliation(s)
- Jakop Schwoerbel
- Institute for Marine and Antarctic Studies, Battery Point, Tasmania, Australia
| | - Wouter Visch
- Institute for Marine and Antarctic Studies, Battery Point, Tasmania, Australia
| | - Jeffrey T Wright
- Institute for Marine and Antarctic Studies, Battery Point, Tasmania, Australia
| | - Alecia Bellgrove
- School of Life and Environmental Sciences, Centre for Marine Science, Deakin University, Warrnambool, Victoria, Australia
| | | | - Catriona L Hurd
- Institute for Marine and Antarctic Studies, Battery Point, Tasmania, Australia
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Supratya VP, Martone PT. Kelps on demand: Closed-system protocols for culturing large bull kelp sporophytes for research and restoration. JOURNAL OF PHYCOLOGY 2024; 60:73-82. [PMID: 38102853 DOI: 10.1111/jpy.13413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2023] [Revised: 11/06/2023] [Accepted: 11/07/2023] [Indexed: 12/17/2023]
Abstract
Culturing kelps for commercial, conservation, and scientific purposes is becoming increasingly widespread. However, kelp aquaculture methods are typically designed for ocean-based farms, and these methods may not be applicable for smaller scale cultivation efforts common in research and restoration. Growing kelps in closed, recirculating culture systems may address many of these constraints, yet closed system approaches have remained largely undescribed. Extensive declines of the bull kelp (Nereocystis luetkeana), an ecologically important canopy species in the Northeast Pacific, have received widespread attention and prompted numerous research and conservation initiatives. Here, we detail two approaches for cultivating N. luetkeana sporophytes in closed recirculating systems. Nereocystis luetkeana were reared as attached thalli in custom seaweed growth flumes and also free-floating in tumble culture tanks. Careful control of stocking density, water motion, aeration, and nutrient levels allowed for rapid growth and normal morphogenesis of laboratory-grown kelp. Culture systems reached up to 3 kg · m-3 , and individual thalli attained lengths of up to 6 m before the trials were terminated. Our results demonstrate the potential of recirculating, closed culture systems to overcome limitations associated with traditional culture methods. Recirculating systems enable the precise control of culture conditions, improving biosecurity and facilitating cultivar development and other research. Kelps can be grown away from the ocean or outside their native ranges, and seasonal or annual species can be produced year-round without seasonal constraints.
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Affiliation(s)
- Varoon P Supratya
- Department of Botany and Beaty Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada
| | - Patrick T Martone
- Department of Botany and Beaty Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada
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Britton D, Layton C, Mundy CN, Brewer EA, Gaitán-Espitia JD, Beardall J, Raven JA, Hurd CL. Cool-edge populations of the kelp Ecklonia radiata under global ocean change scenarios: strong sensitivity to ocean warming but little effect of ocean acidification. Proc Biol Sci 2024; 291:20232253. [PMID: 38228502 DOI: 10.1098/rspb.2023.2253] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Accepted: 12/04/2023] [Indexed: 01/18/2024] Open
Abstract
Kelp forests are threatened by ocean warming, yet effects of co-occurring drivers such as CO2 are rarely considered when predicting their performance in the future. In Australia, the kelp Ecklonia radiata forms extensive forests across seawater temperatures of approximately 7-26°C. Cool-edge populations are typically considered more thermally tolerant than their warm-edge counterparts but this ignores the possibility of local adaptation. Moreover, it is unknown whether elevated CO2 can mitigate negative effects of warming. To identify whether elevated CO2 could improve thermal performance of a cool-edge population of E. radiata, we constructed thermal performance curves for growth and photosynthesis, under both current and elevated CO2 (approx. 400 and 1000 µatm). We then modelled annual performance under warming scenarios to highlight thermal susceptibility. Elevated CO2 had minimal effect on growth but increased photosynthesis around the thermal optimum. Thermal optima were approximately 16°C for growth and approximately 18°C for photosynthesis, and modelled performance indicated cool-edge populations may be vulnerable in the future. Our findings demonstrate that elevated CO2 is unlikely to offset negative effects of ocean warming on the kelp E. radiata and highlight the potential susceptibility of cool-edge populations to ocean warming.
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Affiliation(s)
- Damon Britton
- Institute for Marine and Antarctic Studies, University of Tasmania, 20 Castray Esplanade, Battery Point, Hobart, Tasmania 7004, Australia
| | - Cayne Layton
- Institute for Marine and Antarctic Studies, University of Tasmania, 20 Castray Esplanade, Battery Point, Hobart, Tasmania 7004, Australia
| | - Craig N Mundy
- Institute for Marine and Antarctic Studies, University of Tasmania, 20 Castray Esplanade, Battery Point, Hobart, Tasmania 7004, Australia
| | | | - Juan Diego Gaitán-Espitia
- School of Biological Sciences and the SWIRE Institute of Marine Sciences, The University of Hong-Kong, Hong Kong, People's Republic of China
| | - John Beardall
- School of Biological Sciences, Monash University, Clayton, Victoria 3800, Australia
| | - John A Raven
- Division of Plant Science, University of Dundee at the James Hutton Institute, Invergowrie, Dundee DD2 5DA, UK
- School of Biological Sciences, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia
- Climate Change Cluster, University of Technology, Sydney, Ultimo, New South Wales 2007, Australia
| | - Catriona L Hurd
- Institute for Marine and Antarctic Studies, University of Tasmania, 20 Castray Esplanade, Battery Point, Hobart, Tasmania 7004, Australia
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Weigel BL, Small SL, Berry HD, Dethier MN. Effects of temperature and nutrients on microscopic stages of the bull kelp (Nereocystis luetkeana, Phaeophyceae). JOURNAL OF PHYCOLOGY 2023; 59:893-907. [PMID: 37497792 DOI: 10.1111/jpy.13366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Revised: 06/23/2023] [Accepted: 06/27/2023] [Indexed: 07/28/2023]
Abstract
Warming ocean temperatures have been linked to kelp forest declines worldwide, and elevated temperatures can act synergistically with other local stressors to exacerbate kelp loss. The bull kelp Nereocystis luetkeana is the primary canopy-forming kelp species in the Salish Sea, where it is declining in areas with elevated summer water temperatures and low nutrient concentrations. To determine the interactive effects of these two stressors on microscopic stages of N. luetkeana, we cultured gametophytes and microscopic sporophytes from seven different Salish Sea populations across seven different temperatures (10-22°C) and two nitrogen concentrations. The thermal tolerance of microscopic gametophytes and sporophytes was similar across populations, and high temperatures were more stressful than low nitrogen levels. Additional nitrogen did not improve gametophyte or sporophyte survival at high temperatures. Gametophyte densities were highest between 10 and 16°C and declined sharply at 18°C, and temperatures of 20 and 22°C were lethal. The window for successful sporophyte production was narrower, peaking at 10-14°C. Across all populations, the warmest temperature at which sporophytes were produced was 16 or 18°C, but sporophyte densities were 78% lower at 16°C and 95% lower at 18°C compared to cooler temperatures. In the field, bottom temperatures revealed that the thermal limits of gametophyte growth (18°C) and sporophyte production (16-18°C) were reached during the summer at multiple sites. Prolonged exposure of bull kelp gametophytes to temperatures of 16°C and above could limit reproduction, and therefore recruitment, of adult kelp sporophytes.
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Affiliation(s)
- Brooke L Weigel
- Friday Harbor Labs, University of Washington, Friday Harbor, Washington, USA
| | - Sadie L Small
- Friday Harbor Labs, University of Washington, Friday Harbor, Washington, USA
| | - Helen D Berry
- Washington State Department of Natural Resources, Olympia, Washington, USA
| | - Megan N Dethier
- Friday Harbor Labs, University of Washington, Friday Harbor, Washington, USA
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