Catastrophic loss of tropical seagrass habitats at the Cocos (Keeling) Islands due to multiple stressors

Buckee, Joanna; Hetzel, Yasha; Nyegaard, Marianne; Evans, Scott N.; Whiting, Scott D.; Scott, Sarah; Ayvazian, Suzanne G.; Keulen, M. van; Verduin, Jennifer

doi:10.1016/j.marpolbul.2021.112602

Cited by 8 publications

(4 citation statements)

References 35 publications

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“…The relatively low abundance of herbivores imposing comparatively low grazing pressure, and the rapid recovery of this seagrass suggests that these meadows are resilient to grazing now and into the future. This is unlikely to be the case for other ecosystems with high and/or dense herbivore populations and slower-growing seagrass species (Buckee et al, 2021;Gangal et al, 2021).…”

Section: Discussionmentioning

confidence: 95%

“…Increased grazing pressure can occur as a result of increased herbivore populations ( Choney et al, 2014 ; Kollars et al, 2017 ; Fourqurean et al, 2019 ; Buckee et al, 2021 ), and is already occurring as a result of climate change ( Traill et al, 2009 ). Examples of this include the extension of herbivore distribution ranges due to tropicalisation ( Hyndes et al, 2016 ) or concentration of populations in remaining suitable habitat in drying climates ( Chambers, 2008 ).…”

Section: Discussionmentioning

confidence: 99%

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Increased extent of waterfowl grazing lengthens the recovery time of a colonizing seagrass (Halophila ovalis) with implications for seagrass resilience

et al. 2022

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Herbivore distributions and abundance are shifting because of climate change, leading to intensified grazing pressure on foundation species such as seagrasses. This, combined with rapidly increasing magnitudes of change in estuarine ecosystems, may affect seagrass resilience. While the overall resilience of seagrasses is generally well-studied, the timeframes of recovery has received comparatively little attention, particularly in temperate estuaries. We investigated how the recovery time (RT) of seagrass is affected by simulated grazing in a southwestern Australian estuary. Whilst excluding swans, we simulated different grazing intensities (25, 50, 75, and 100% removal from 1 m2 plots) at four locations in the Swan-Canning Estuary, Western Australia during summer and tracked the recovery of seagrass over 3 months, using seagrass cover as the main measure of recovery. We found that seagrass recovered within 4–6 weeks from the lower grazing intensities (25 and 50%) and 7–19 weeks from the higher grazing intensities (75 and 100%) across the estuary. Increased grazing intensity led to not only longer recovery times (RTs), but also greater variability in the RT among experimental locations. The RT from the higher grazing intensities at one location in particular was more than double other locations. Seagrass recovery was through vegetative mechanisms and not through sexual reproduction. There was a significant grazing treatment effect on seagrass meadow characteristics, particularly belowground biomass which had not recovered 3 months following grazing. As the pressure of climate change on estuarine environments increases, these quantified RTs for seagrass provide a baseline for understanding grazing pressure as a singular disturbance. Future work can now examine how grazing and other potentially interacting pressures in our changing climate could impact seagrass recovery even further.

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Section: Discussionmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 99%

Increased extent of waterfowl grazing lengthens the recovery time of a colonizing seagrass (Halophila ovalis) with implications for seagrass resilience

et al. 2022

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“…Although seagrasses and macroalgae can withstand a wide range of increasing temperature, a rapid deleterious effect was observed when the testing temperature reached 42 • C, implying that the irregular warming events, in which temperature rises above 40 • C, though uncommon and brief, will put immense pressure on intertidal seagrasses and macroalgae, thereby affecting productivity and leading to mortality. Although the seagrass and macroalgal dieoff as a result of warming event was never reported in Thailand, it has been recorded in other locations in the tropical bioregions (Carlson et al, 2018;Buckee et al, 2021).…”

Section: Differences In Sensitivity To Warming Among Important Groups Of Tropical Marine Organisms and Species And Its Ecological Relevanmentioning

confidence: 90%

Experimental Assessment of Vulnerability to Warming in Tropical Shallow-Water Marine Organisms

et al. 2021

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Tropical shallow-water habitats represent the marine environments with the greatest biodiversity; however, these habitats are the most vulnerable to climate warming. Corals, seagrasses, and macroalgae play a crucial role in the structure, functions, and processes of the coastal ecosystems. Understanding their growth and physiological responses to elevated temperature and interspecific sensitivity is a necessary step to predict the fate of future coastal community. Six species representatives, including Pocillopora acuta, Porites lutea, Halophila ovalis, Thalassia hemprichii, Padina boryana, and Ulva intestinalis, collected from Phuket, Thailand, were subjected to stress manipulation for 5 days. Corals were tested at 27, 29.5, 32, and 34.5°C, while seagrasses and macroalgae were tested at 27, 32, 37, and 42°C. After the stress period, the species were allowed to recover for 5 days at 27°C for corals and 32°C for seagrasses and macroalgae. Non-destructive evaluation of photosynthetic parameters (Fv/Fm, Fv/F0, ϕPSII and rapid light curves) was carried out on days 0, 3, 5, 6, 8, and 10. Chlorophyll contents and growth rates were quantified at the end of stress, and recovery periods. An integrated biomarker response (IBR) approach was adopted to integrate the candidate responses (Fv/Fm, chlorophyll content, and growth rate) and quantify the overall temperature effects. Elevated temperatures were found to affect photosynthesis, chlorophyll content, and growth rates of all species. Lethal effects were detected at 34.5°C in corals, whereas adverse but recoverable effects were detected at 32°C. Seagrasses and macroalgae displayed a rapid decline in photosynthesis and lethal effects at 42°C. In some species, sublethal stress manifested as slower growth and lower chlorophyll content at 37°C, while photosynthesis remained unaffected. Among all, T. hemprichii displayed the highest thermotolerance. IBR provided evidence that elevated temperature affected the overall performance of all tested species, depending on temperature level. Our findings show a sensitivity that differs among important groups of tropical marine organisms inhabiting the same shallow-water environments and highlights the importance of integrating biomarkers across biological levels to assess their vulnerability to climate warming.

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“…Relative to terrestrial systems, our understanding of interactions between below-ground micro-organisms and marine plants is limited, although emerging evidence suggests that microbially mediated below-ground processes can have a critical role in influencing marine plant performance (Gribben et al, 2017(Gribben et al, , 2018. Marine plants are vulnerable to environmental change and many critical habitatforming seagrass species are already experiencing catastrophic declines (Buckee et al, 2021;Evans et al, 2018;Green et al, 2021;Strydom et al, 2020). Several local and global stressors are contributing to seagrass declines; however, eutrophication driven by anthropogenic nitrogen loading is a major stressor in coastal systems inhabited by seagrasses (Burkholder et al, 2007;Mvungi & Pillay, 2019;Orth et al, 2006;Schmidt et al, 2012;Waycott et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Experimental evidence root‐associated microbes mediate seagrass response to environmental stress

2023

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1. Below-ground microbiota play an important role in mediating environmental conditions with important consequences for plant performance. Micro-organisms involved in plant-soil interactions may be associated with roots or bulk soil; however, the relative influence of these below-ground microbial assemblages on plant performance is poorly known, particularly for marine plants.2. We separately manipulated the root and sediment microbial assemblages of the seagrass Zostera muelleri in a fully factorial experiment to determine how these assemblages determined plant response (e.g. growth) to nutrient enrichment, a major stressor in marine systems.3. Under ambient nutrient conditions, seagrass growth was maintained regardless of root microbial assemblage disruption. Under high nutrient stress, however, seagrasses with disrupted root microbiota had reduced growth, whereas growth was maintained in seagrasses with an intact root microbiota. Disruption of bulksediment microbiota did not affect seagrass growth. Nutrient elevation was correlated with enhanced abundances of several putatively beneficial microbial taxa (e.g. sulphide-oxidising Beggiatoaceae and denitrifying Geofilum rubicundum) associated with roots. 4. Synthesis. Our results suggest that under ambient nutrient conditions microorganisms play a reduced role in influencing plant performance, but under more stressful conditions positive plant-root micro-organism interactions strengthened. These results are among the first to experimentally determine that interactions between marine plants and the root-associated microbiota are key drivers of seagrass performance under human-induced environmental changes. This suggests that as in terrestrial systems, marine plant resilience depends on the stress-mitigating functions of their root-associated microbiota and disturbance to those plant-microbiota interactions can be deleterious for plant performance.Improving our understanding of these plant-micro-organism interactions may be critical for understanding the functioning and resilience of threatened marine plants and developing more effective restoration strategies for them.

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Catastrophic loss of tropical seagrass habitats at the Cocos (Keeling) Islands due to multiple stressors

Cited by 8 publications

References 35 publications

Increased extent of waterfowl grazing lengthens the recovery time of a colonizing seagrass (Halophila ovalis) with implications for seagrass resilience

Increased extent of waterfowl grazing lengthens the recovery time of a colonizing seagrass (Halophila ovalis) with implications for seagrass resilience

Experimental Assessment of Vulnerability to Warming in Tropical Shallow-Water Marine Organisms

Experimental evidence root‐associated microbes mediate seagrass response to environmental stress

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