The pulsating soft coral Xenia umbellata shows high resistance to warming when nitrate concentrations are low

Thobor, Bianca; Tilstra, Arjen; Bourne, David G.; Springer, Karin; Mezger, Selma D.; Struck, Ulrich; Bockelmann, Franziska; Zimmermann, Lisa; Suárez, Ana Belén Yánez; Klinke, Annabell; Wild, Christian

doi:10.1038/s41598-022-21110-w

Cited by 9 publications

(22 citation statements)

References 80 publications

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“…Wiedenmann et al (2013), for instance, observed that corals previously incubated at high N:P ratios (< 5 weeks) displayed signs of bleaching within 10 days when exposed to a stepwise increase in heat (up to 30°C) and light (up to 160 mmol m ¬2 s ¬1 ) stress due to phosphate starvation. Supporting results were observed by Thobor et al (2022), who found a higher susceptibility of X. umbellata to ocean warming when previously exposed to nitrate enrichment (37 µM) for two weeks followed by a combined treatment of nitrate enrichment and a stepwise temperature increase from 26 to 32°C in three weeks. However, X. umbellata colonies in the present study were not exposed to high N:P ratios and thus should not suffer from phosphate starvation.…”

Section: Phosphate Enrichment Did Not Affect Symbiotic Symbiodiniaceaesupporting

confidence: 75%

“…Recently, Vollstedt et al (2020) observed that the pulsating soft coral Xenia umbellata benefits from organic eutrophication (in form of glucose), resulting in an increased resilience to warming. In contrast, inorganic eutrophication (in form of nitrate) decreased the resilience of X. umbellata to warming (Thobor et al, 2022) supporting the finding of Wiedenmann et al (2013): high N:P ratios can decrease the resilience of corals to warming, possibly due to a destabilized symbiosis between the coral host and its Symbiodiniaceae following phosphate starvation. Phosphate generally plays an important role during thermal stress in corals by maintaining Symbiodiniaceae density and photosynthetic rates (Ezzat et al, 2016).…”

Section: Introductionsupporting

confidence: 70%

“…Afterwards, the tower system was disconnected from the main system and tanks were separated at the start of the experiment (day 0) to ensure equal starting water conditions across treatments. Further, the temperature in each tank was increased to ~26°C (1°C per day) to commensurate experimental conditions of previous studies (Vollstedt et al, 2020;Thobor et al, 2022). 10% of the artificial seawater was replaced daily to maintain a high water renewal rate in each tank.…”

Section: Experimental Design and Conditionsmentioning

confidence: 99%

“…This procedure was repeated until the final water temperature of 32°C was reached. The selected temperature treatment was based on the experimental design of previous studies investigating the combined effect of organic/ inorganic eutrophication and ocean warming on X. umbellata (Vollstedt et al, 2020;Thobor et al, 2022).…”

Section: Experimental Phosphate and Temperature Treatmentsmentioning

confidence: 99%

“…The pulsating soft coral X. umbellata was used as a study organism because it is a common species in the Indo-Pacific region (Benayahu, 1990;Fabricius and Klumpp, 1995;Fox et al, 2003;Janes, 2013). We hypothesize that phosphate, in contrast to nitrate, will increase the resilience of X. umbellata to warming because its Symbiodiniaceae will not suffer from phosphate starvation (Wiedenmann et al, 2013;Rädecker et al, 2015;Thobor et al, 2022). We tested our hypothesis in a five-week laboratory experiment with two phases.…”

Section: Introductionmentioning

confidence: 99%

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Phosphate enrichment increases the resilience of the pulsating soft coral Xenia umbellata to warming

et al. 2022

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Hard corals are in decline as a result of the simultaneous occurrence of global (e.g., ocean warming) and local (e.g., inorganic eutrophication) factors, facilitating phase shifts towards soft coral dominated reefs. Yet, related knowledge about soft coral responses to anthropogenic factors remains scarce. We thus investigated the ecophysiological response of the pulsating soft coral Xenia umbellata to individual and combined effects of phosphate enrichment (1, 2, and 8 μM) and ocean warming (26 to 32°C) over 35 days. Throughout the experiment, we assessed pulsation, mortality, Symbiodiniaceae density, and cellular chlorophyll a content. Simulated ocean warming up to 30°C led to a significant increase in polyp pulsation and by the end of the experiment to a significant increase in Symbiodiniaceae density, whereas cellular chlorophyll a content significantly decreased with warming, regardless of the phosphate treatment. The combination of phosphate enrichment and simulated ocean warming increased pulsation significantly by 41 – 44%. Warming alone and phosphate enrichment alone did not affect any of the investigated response parameters. Overall, X. umbellata displayed a high resilience towards ocean warming with no mortality in all treatments. Phosphate enrichment enabled soft corals to significantly increase their pulsation under increasing temperatures which may enhance their resilience towards ocean warming. This, in turn, could further facilitate their dominance over hard corals on future reefs.

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Section: Phosphate Enrichment Did Not Affect Symbiotic Symbiodiniaceaesupporting

confidence: 75%

Section: Introductionsupporting

confidence: 70%

Section: Experimental Design and Conditionsmentioning

confidence: 99%

Section: Experimental Phosphate and Temperature Treatmentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Phosphate enrichment increases the resilience of the pulsating soft coral Xenia umbellata to warming

et al. 2022

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Physiology of the widespread pulsating soft coralXenia umbellatais affected by food sources, but not by water flow

Hill,

Abbass,

Caporale

et al. 2023

Ecology and Evolution

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Coral energy and nutrient acquisition strategies are complex and sensitive to environmental conditions such as water flow. While high water flow can enhance feeding in hard corals, knowledge about the effects of water flow on the feeding of soft corals, particularly those pulsating, is still limited. In this study, we thus investigated the effects of feeding and water flow on the physiology of the pulsating soft coral Xenia umbellata. We crossed three feeding treatments: (i) no feeding, (ii) particulate organic matter (POM) in the form of phytoplankton and (iii) dissolved organic carbon (DOC) in the form of glucose, with four water volume exchange rates (200, 350, 500 and 650 L h−1) over 15 days. Various ecophysiological parameters were assessed including pulsation rate, growth rate, isotopic and elemental ratios of carbon (C) and nitrogen (N) as well as photo‐physiological parameters of the Symbiodiniaceae (cell density, chlorophyll‐a and mitotic index). Water flow had no significant effect but feeding had a substantial impact on the physiology of the X. umbellata holobiont. In the absence of food, corals exhibited significantly lower pulsation rates, lower Symbiodiniaceae cell density and lower mitotic indices compared to the fed treatments, yet significantly higher chlorophyll‐a per cell and total N content. Differences were also observed between the two feeding treatments, with significantly higher pulsation rates and lower chlorophyll‐a per cell in the DOC treatment, but higher C and N content in the POM treatment. Our findings suggest that the X. umbellata holobiont can be viable under different trophic strategies, though favouring mixotrophy. Additionally, the physiology of the X. umbellata may be regulated through its own pulsating behaviour without any positive or negative effects from different water flow. Therefore, this study contributes to our understanding of soft coral ecology, particularly regarding the competitive success and widespread distribution of X. umbellata.

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Excess particulate organic matter negatively affects the ecophysiology of the widespread soft coral Xenia umbellata

Hill,

Rücker,

Eichhorn

et al. 2024

Mar Biol

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Coastal coral reefs are experiencing rising concentrations of organic matter. While dissolved organic matter (DOM), rather than particulate organic matter (POM), may negatively impact hard corals, the impact on soft corals remains unclear. We examined the physiological effect of 20 mg L−1 of organic carbon (C) addition on the widespread Indo-Pacific soft coral Xenia umbellata in a series of tank experiments over 28 days. We supplied DOM as glucose, and two POM sources as phytoplankton (2–5 μm length) and zooplankton (150–200 μm length). We comparatively assessed coral morphology, pulsation, colouration, algal symbiont densities, chlorophyll a, oxygen fluxes, and mortality. Corals in the control and DOM enrichment treatments exhibited no morphological or physiological changes, whereas, excess phyto- and zooplankton caused disfigurement of the polyp tentacles and shortening of its pinnules. This coincided with a mortality of 11 and 14%, respectively, a 35% reduction in pulsation rates, and darkening of the polyps (with excess zooplankton), while other assessed response variables remained stable. This suggests that in contrast to many hard corals, the soft coral X. umbellata is vulnerable to excess POM rather than DOM, with amplified effects upon exposure to larger particles. Our results suggest that excess POM may damage the delicate feeding apparatus of X. umbellata, thereby reducing pulsation and lowering gas exchange. In turn, this can cause nutritional, and ultimately, energy deficiencies by directly affecting heterotrophic and autotrophic feeding. Our findings indicate that the global-change-resilient soft coral X. umbellata is vulnerable to local eutrophication, particularly high concentrations of POM.

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The pulsating soft coral Xenia umbellata shows high resistance to warming when nitrate concentrations are low

Cited by 9 publications

References 80 publications

Phosphate enrichment increases the resilience of the pulsating soft coral Xenia umbellata to warming

Phosphate enrichment increases the resilience of the pulsating soft coral Xenia umbellata to warming

Physiology of the widespread pulsating soft coralXenia umbellatais affected by food sources, but not by water flow

Excess particulate organic matter negatively affects the ecophysiology of the widespread soft coral Xenia umbellata

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