Marine Pollution as a Trigger of Discoloration Phenomenon in The Hard Coral, Pocillopora Species at The Gulf of Aqaba, Red Sea, Egypt: Pathological and Molecular Evidences

Hard corals are precious marine creatures that comprise a complex form of symbiosis between symbiont algae and coral holobiont. For decades, corals have been challenged by disastrous events of climatic and anthropogenic etiologies. Such complex interactions have resulted in devastating disease episodes among coral populations worldwide. There is a scarcity of information about diseases of hard corals in the Gulf of Aqaba, Red Sea, Egypt. Therefore, the current study aims to investigate various diseases of hard corals in this pristine habitat within the Red Sea. Whitening and dark green dots were the most noticeable morphopathology among hard coral samples collected from Gulf of Aqaba. Some human-based pathogens, such as Rothia kristinae, Cupriavidus pauculus, and Delftia acidovorans, were isolated from some of the examined coral tissues, while the Burkholderia cepacia group was isolated from the nearby sediment. The final identities of the above-mentioned bacterial isolates have been molecularly confirmed using 16S RNA sequence analysis. Pathologically, diseased corals have been observed with changes such as some forms of tissue losses, degenerative changes, and eosinophilic granular amoebocytes/agranular cells infiltration. The frequent detection of some microbial pathogens of human origin could suggest deleterious forms of environmental pollution of anthropogenic origin. Ultimately, the entire existence of hard coral populations is mostly threatened by swiftly erupting climatic changes as well as environmental aquatic pollution. Thus, the current study concludes the real need for extensive ecological, biological, pathological, and immunological studies to determine the eminent threats and propose possible control means for better/sustainable hard coral populations.