Most reef aquarists are familiar with coral’s symbiotic relationship with zooxanthellae algae. These tiny algae are responsible for providing corals with nutrition, in the form of sucrose which is over-produced during photosynthesis. Scientists have uncovered that coral’s have another (possible equally as important) organism living with them. In keeping in line with my recent posts on marine microbes, I thought it pertinent to discuss the relationship between corals and various species of marine bacteria. Many aquarists don’t realize the extent of this relationship. Various bacteria actually produce antibiotic which helps heal coral infections, and establish networks of bacterial communication, literally serving as coral’s microscopic caretakers. Since we are just beginning to understand the importance of microbes in the marine ecosystem, it’s also vital to understand how remarkably crucial earth’s tiniest organisms are to living corals. Coral/bacteria relationship:
At MOTE: the marine laboratory and aquarium in Sarasota Florida, researchers set out to understand how microbes and corals interact. They first assessed a baseline of microbial communities within both threatened and healthy coral species. The goal was to understand what role microbes play in health and disease, and what benefits they provide to overall resistance and antibiotic production. Researchers paid careful attention to bacterial associations with coral that produced antibiotics, and other beneficial compounds. What they found, is that microbes literally communicate with the host coral, ordering events to take place at the coral’s surface. This complex symbiosis occurs between marine microbes, the host coral and zooanthellae algae. An entire network of communication and care provided by a multitude of organisms, including the host coral itself. Researchers learned that corals harbor specific microbes that shift pathogen dominance when temperatures increase. The Symbiodinium sp. species of coral was host to large colonies of Roseobacterials. The bacteria was found to increase symbiodinium growth rates, while producing quorum sensing (bacterial communication) compounds that aided in coral larvae settlement rates. Bacteria was literally aiding and accelerating coral growth, while helping larvae settle in appropriate conditions. 
A bacterium was also found to produce gene transfer agents (GTA) which facilitate rapid acclimation to environmental change. This means that bacteria can aid new coral larvae in acquiring the genes required to adapt to a changing climate, or acclimate to a new set of environmental conditions. MOTE along with the University of South Florida’s Marine Science department have completely sequenced the genes of some of these highly beneficial coral bacteria.… More:
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