The widely distributed soft coral Xenia umbellata exhibits high resistance against phosphate enrichment and temperature increase

Abstract

Both global and local factors affect coral reefs worldwide, sometimes simultaneously. An interplay of these factors can lead to phase shifts from hard coral dominance to algae or other invertebrates, particularly soft corals. However, most studies have targeted the effects of single factors, leaving pronounced knowledge gaps regarding the effects of combined factors on soft corals. Here, we investigated the single and combined effects of phosphate enrichment (1, 2, and 8 μM) and seawater temperature increase (26 to 32 °C) on the soft coral Xenia umbellata by quantifying oxygen fluxes, protein content, and stable isotope signatures in a 5-week laboratory experiment. Findings revealed no significant effects of temperature increase, phosphate enrichment, and the combination of both factors on oxygen fluxes. However, regardless of the phosphate treatment, total protein content and carbon stable isotope ratios decreased significantly by 62% and 7% under temperature increase, respectively, suggesting an increased assimilation of their energy reserves. Therefore, we hypothesize that heterotrophic feeding may be important for X. umbellata to sustain their energy reserves under temperature increase, highlighting the advantages of a mixotrophic strategy. Overall, X. umbellata shows a high tolerance towards changes in global and local factors, which may explain their competitive advantage observed at many Indo-Pacific reef locations.

Short-term ocean acidification decreases pulsation and growth of the widespread soft coral Xenia umbellata

“…Stable isotope signatures and CN content. To assess the effects of increased DIC on the isotope signatures and elemental composition of holobiont C and N, six samples from both treatments, i.e., one colony per tank, were taken at the end of the experiment (day 21) and prepared according to Mezger and colleagues [53]. Briefly, colonies were carefully detached from the plug and thoroughly rinsed with distilled water to eliminate any traces of salt.…”

Shifts in dominance of benthic communities along a gradient of water temperature and turbidity in tropical coastal ecosystems

“…Sponges are predicted to become more dominant in tropical reefs due to their resilience to rising sea temperatures, as well as their potential to outcompete certain coral species under changing environmental conditions ( Bell et al, 2013 ; Bell et al, 2018 ; de Bakker et al, 2017 ; Pawlik & McMurray, 2020 ). There has been a possible shift noticed to soft coral dominance in benthic communities in tropical coastal ecosystems in the Indo-Pacific because soft coral may be more resistant to warming temperatures and nutrient enrichment than hard coral ( Baum et al, 2016 ; Mezger et al, 2022 ; Reverter et al, 2022 ). Shifts from coral-dominated reefs to reefs dominated by other taxonomic groups can negatively affect the coral reef ecosystem ( Hughes et al, 2010 ; Tebbett, Connolly & Bellwood, 2023a ), since these shifts can lead to decreases in structural complexity ( Alvarez-filip et al, 2009 ), and a reduction in both habitat availability for various reef species ( Graham & Nash, 2013 ) and ecological functions within the food webs ( Ford et al, 2018 ; Nelson, Kelly & Haas, 2022 ; Mortimer et al, 2023 ).…”

“…Most relevant research to date has focused on the ecological responses of reefs (time scales of several decades and under ambient temperature conditions ( de Bakker et al, 2017 ; Giorgi et al, 2022 ; Caballero-aragón et al, 2023 ) or of selected species within an experimental set up of a coral reef community to increased temperatures over short time scales (weeks/months; Ullah et al, 2018 ; Grottoli et al, 2021 ; Mezger et al, 2022 ), yet little is known about the long-term response of whole communities to changes in temperature and environmental conditions. Marine lakes with high water temperatures and high turbidity may provide insights into potential shifts in dominance of benthic groups in tropical coastal ecosystems ( Hamner & Hamner, 1998 ; Becking et al, 2011 ; Maas et al, 2023 ).…”

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

“…However, whether X. umbellata has a preferred or more dominant feeding mode is unclear. Whilst soft corals are generally considered as more heterotrophic (Pupier et al, 2021), X. umbellata has demonstrated a higher photosynthetic productivity compared to other soft corals, with the ability to sustain its energetic needs by net autotrophy alone (Mezger et al, 2022). Yet, other studies suggest that X. umbellata relies more on heterotrophic suspension feeding because of its morphology and biochemical composition (Al‐Sofyani & Niaz, 2007).…”

“…In another study, Ovabunda macrospiculata (Gohar, 1940) demonstrated a resistance to high pco 2 conditions (Gabay et al, 2014). One species in particular, namely Xenia umbellata (Lamarck, 1816), has displayed resistance to warming (Mezger et al, 2022; Thobor et al, 2022), organic eutrophication (Simancas‐Giraldo et al, 2021; Vollstedt et al, 2020) and phosphate enrichment (Klinke et al, 2022; Mezger et al, 2022), with its success across all these studies attributed to its trophic plasticity.…”