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

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.

The effects of an obesogenic diet on behavior and cognition in zebrafish (Danio rerio): Trait average, variability, repeatability, and behavioral syndromes.

The obesity epidemic, largely driven by the accessibility of ultra-processed high-energy foods, is one of the most pressing public health challenges of the 21st century. Consequently, there is increasing concern about the impacts of diet-induced obesity on behavior and cognition. While research on this matter continues, to date, no study has explicitly investigated the effect of obesogenic diet on variance and covariance (correlation) in behavioral traits. Here, we examined how an obesogenic versus control diet impacts means and (co-)variances of traits associated with body condition, behavior, and cognition in a laboratory population of ~160 adult zebrafish (Danio rerio). Overall, an obesogenic diet increased variation in several zebrafish traits. Zebrafish on an obesogenic diet were significantly heavier and displayed higher body weight variability; fasting blood glucose levels were similar between control and treatment zebrafish. During behavioral assays, zebrafish on the obesogenic diet displayed more exploratory behavior and were less reactive to video stimuli with conspecifics during a personality test, but these significant differences were sex-specific. Zebrafish on an obesogenic diet also displayed repeatable responses in aversive learning tests whereas control zebrafish did not, suggesting an obesogenic diet resulted in more consistent, yet impaired, behavioral responses. Where behavioral syndromes existed (inter-class correlations between personality traits), they did not differ between obesogenic and control zebrafish groups. By integrating a multifaceted, holistic approach that incorporates components of (co-)variances, future studies will greatly benefit by quantifying neglected dimensions of obesogenic diets on behavioral changes.

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

The resistance of hard corals to warming can be negatively affected by nitrate eutrophication, but related knowledge for soft corals is scarce. We thus investigated the ecophysiological response of the pulsating soft coral Xenia umbellata to different levels of nitrate eutrophication (control = 0.6, medium = 6, high = 37 µM nitrate) in a laboratory experiment, with additional warming (27.7 to 32.8 °C) from days 17 to 37. High nitrate eutrophication enhanced cellular chlorophyll a content of Symbiodiniaceae by 168%, while it reduced gross photosynthesis by 56%. After additional warming, polyp pulsation rate was reduced by 100% in both nitrate eutrophication treatments, and additional polyp loss of 7% d-1 and total fragment mortality of 26% was observed in the high nitrate eutrophication treatment. Warming alone did not affect any of the investigated response parameters. These results suggest that X. umbellata exhibits resistance to warming, which may facilitate ecological dominance over some hard corals as ocean temperatures warm, though a clear negative physiological response occurs when combined with nitrate eutrophication. This study thus confirms the importance of investigating combinations of global and local factors to understand and manage changing coral reefs.