Exhibition of Bleaching Resistance Via Adaptive Bleaching Pattern by Coral Reefs of the Gulf of Mannar during Massive Bleaching Event 2019

Coral reefs in the Gulf of Mannar(GoM)and Palk Bay regions are facing potential threats from climate change,sedimentation and anthropogenic activities.Considerably,coral reefs in these two regions are highly damaged due to frequent bleaching events caused by increased sea surface temperature(SST)recorded over the past two decades.Recently,during February to May 2019,mass bleaching event of corals was documented again in GoM and Palk Bay regions due to increased sea surface temperatures ranged between 32°C to 36°C.Despite of completely bleached corals,some coral colonies of the same bleached coral species have displayed adaptive bleaching pattern(ABP)for survival.This incidence is displayed by the symbiotic zooxanthellae to protect coral polyps from environmental stress such as elevated temperatures.These observations infer that coral colonies with preferential bleaching pattern ability would serve as environmental stress resisting coral colonies which can be used for restoration activities and cryopreservation.Further studies are needed to explain the potential mechanisms or specific environmental drivers responsible for ABP.

Expression analyses of stress‑responsive genes in the hermatypic coral Acropora tenuis and its symbiotic dinofagellates after exposure to the herbicide Diuron

Diuron is one of the most frequently applied herbicides in sugarcane farming in southern Japan,and Australia.In addition,it is used as a booster substance in copper-based antifouling paints.Due to these various uses,Diuron is released into the marine environment;however,little information is available on gene expression in corals and their symbiotic algae exposed to Diuron.We investigated the efects of Diuron on stress-responsive gene expression in the hermatypic coral Acropora tenuis and its symbiotic dinofagellates.After seven days of exposure to 1µg/L and 10µg/L Diuron,no signifcant changes in the body colour of corals were observed.However,quantitative reverse transcription-polymerase chain reaction analyses revealed that the expression levels of stress-responsive genes,such as heat shock protein 90(HSP90),HSP70,and calreticulin(CALR),were signifcantly downregulated in corals exposed to 10µg/L of Diuron for seven days.Moreover,aquaglyceroporin was signifcantly downregulated in corals exposed to environmentally relevant concentrations of 1µg/L Diuron.In contrast,no such efects were observed on the expression levels of other stress-responsive genes,such as oxidative stress-responsive proteins,methionine adenosyltransferase,and green/red fuorescent proteins.Diuron exposure had no signifcant efect on the expression levels of HSP90,HSP70,or HSP40 in the symbiotic dinofagellates.These results suggest that stress-responsive genes,such as HSPs,respond diferently to Diuron in corals and their symbiotic dinofagellates and that A.tenuis HSPs and CALRs may be useful molecular biomarkers for predicting stress responses induced by the herbicide Diuron.