Validating the use of ROS-scavenging bacteria as probiotics to increase coral resilience to thermal stress

Thermal stress causes the overproduction and toxic accumulation of reactive oxygen species(ROS),which seems to be correlated with coral bleaching and,ultimately,death.The reduction of ROS concentration within the coral holobiont could minimize the effects of thermal stress and support efforts to reduce coral decline globally.In the current study,we explored the physiological responses of Pocillopora damicornis to ROS-scavenging bacteria inoculation as well as the microbiome restructuring that correlates with P.damicornis’s resilience to thermal stress after probiotic inoculation.Inoculation of corals with ROS-scavenging bacteria enhanced coral health and reduced ROS concentration.Furthermore,the enhanced coral thermal resistance promoted by ROS-scavenging bacteria was also correlated with an overall coral microbiome restructuring.In addition,the complex network relationships between bacteria and Symbiodiniaceae in corals after ROS-scavenging bacteria inoculation contributed to corals’resilience to high temperatures.Besides,coral heat tolerance bacterial biomarkers,such as Myxococcota,were enriched in corals with added ROS-scavenging bacteria.Collectively,our findings validate the selected ROS-scavenging bacteria as coral probiotics that could help corals resist thermal stress on a short timescale.Additionally,our data contribute to our understanding of the potential interactions between different members of the coral holobiont and the use of probiotics as tools to aid coral restoration efforts.

Molecular quantification of copepod Acartia erythraea feeding on different algae preys

Quantitative evaluation of the copepod feeding process is critical for understanding the functioning of marine food webs, as this provides a major link between primary producers and higher trophic levels. In this study, a molecular protocol based on quantitative polymerase chain reaction(qPCR) targeting 18S rDNA was developed and used to investigate the feeding and digestion rates of the copepod Acartia erythraea in a laboratory experiment using microalgae Thalassiosira weissflogii, Prorocentrum shikokuense, and Alexandrium catenella as prey. Although offered an equal encounter rate based on biovolume, prey uptake varied substantially among the three algal species, with the ingestion rate(IR) and digestion rate(DR) of A. erythraea differing significantly(P <0.001) based on both cell counting and qPCR detection. Acartia erythraea showed the highest IR(2.79×10~4 cells/(ind.·h)) and DR(2.43×10~4 cells/(ind.·h)) on T. weissflogii, and the lowest amounts of ingested P. shikokuense were detected. The highest assimilation rate(~90.64%, IR/DR) was observed in copepods fed with P. shikokuense. The qPCR method used here can help determine the digestion rate and assimilation rate of copepods by detecting cells remaining in the gut hence providing the possibility to examine trophic links involving key species in the marine ecosystem. Our results indicate that A. erythraea has diet-specific feeding performance in different processes, and a quantitative assessment of copepod feeding is needed to accurately determine its functional role in the energy and matter uptake from marine food webs.

Increased light availability enhances tolerance against ocean acidification-related stress in the calcifying macroalga Halimedaopuntia

Although the adverse impacts of ocean acidification(OA)on marine calcifiers have been investigated extensively,the anti-stress capabilities regulated by increased light availability are unclear.Herein,the interactive effects of three light levels(30μmol photons/(m^(2)·s),150μmol photons/(m^(2)·s),and 240μmol photons/(m^(2)·s)combined with two pCO_(2)concentrations(400 ppmv and 1400 ppmv)on the physiological acclimation of the calcifying macroalga Halimeda opuntia were investigated using a pCO_(2)-light coupling experiment.The OA negatively influenced algal growth,calcification,photosynthesis,and other physiological performances in H.opuntia.The relative growth rate under elevated pCO_(2)conditions significantly declined by 13.14%−41.29%,whereas net calcification rates decreased by nearly three-fold under OA conditions.Notably,increased light availability enhanced stress resistance through the accumulation of soluble organic molecules,especially soluble carbohydrate,soluble protein,and free amino acids,and in combination with metabolic enzyme-driven activities,OA stress was alleviated.The carotenoid content under low light conditions increased markedly,and the rapid light curve of the relative electron transport rate was enhanced significantly by increasing light intensities,indicating that this new organization of the photosynthetic machinery in H.opuntia accommodated light variations and elevated pCO_(2)conditions.Thus,the enhanced metabolic performance of the calcifying macroalga H.opuntia mitigated OA-related stress.