Soft Coral Activity Change Under Acute Temperature Stress And Hyperspectral Image Analysis

Coral reef ecosystems are rich in biodiversity and are important homes for marine life to survive.However,under the influence of global warming,the stable and healthy development of coral reef ecology is seriously threatened,and the degradation of coral reefs is obvious on a global scale.According to the survey,the increase of global average coral cover from 2002 to 2009 and 2019 indicates that many coral reefs in the world still have the ability to heal themselves and can recover under suitable environment.Temperature,as the main cause of coral bleaching,has not been reported on the response mechanism of soft corals to different temperature stresses combined with hyperspectral images.In this study,we intend to investigate the response of corals to warming and low temperature stress by conducting short-term acute temperature stress simulation experiments on soft corals.At the same time,underwater hyperspectral imaging was used to collect the spectral images of corals under different ambient temperatures to investigate the changes of coral spectra under temperature stress and provide important information support for coral reef ecosystem monitoring and conservation.In this study,the coral species in the experiment was identified as Sinularia leptoclados by DNA extraction,molecular sequencing and morphology,and the coral chlorophyll content and its response to temperature change were analyzed by conducting temperature stress simulation experiments on soft corals in the laboratory.The changes of coral superoxide dismutase(SOD),catalase(CAT),alkaline phosphatase(AKP)and glutathione S-transferase(GST)enzyme activities were used to determine the changes of coral growth status of soft corals after short-term acute temperature stress,and to provide data basis for coral reef ecosystem monitoring and protection.Through the analysis of coral physiological indexes,the response mechanism of corals when subjected to temperature stress may be: the increase of temperature leads to coral de-algae and the freeing of Cordyceps to the environment,resulting in the decrease of chlorophyll content in corals.Due to the increase in temperature and loss of Cordyceps,the content of reactive oxygen species(ROS)in coral cells increased.The increase in the content of reactive oxygen species further activated the secretion of antioxidant enzymes,which led to the increase in the activities of SOD and CAT enzymes.the expression of GST was related to the change in temperature,with the increase in GST activity when the temperature increased and the decrease in GST activity when the temperature decreased.The AKP activity increased significantly in increasing temperature stress;in cooling stress,there was no significant change in AKP activity,probably due to the small temperature reduction.From the analysis of the spectra,it was obtained that the coral had obvious double peaks at 580 nm and 605 nm,while after 690 nm,there was an obvious red-edge effect and a sharp increase in reflectance spectra.The loss of Cordyceps caused the coral cells to become lighter in color,and the correlation between spectral changes and coral health status was studied by combining the analysis of reflectance spectra with physiological indicators.Based on the analysis of the characteristic wavelengths,the reflectance changes at 580 nm,605 nm and 675 nm in the coral spectra were compared,and the judgment of whether the coral is in the non-healthy state of algae loss was obtained,which provides the basis for the judgment of coral health state by underwater hyperspectral technology in the field of marine monitoring.