Biodiversity refers to the variety of life forms, including species diversity, genetic diversity, and ecosystem diversity. The Great Barrier Reef is a biodiversity hotspot, ranging over 9000 known species. However, since the 1950’s half of the living corals on the Great Barrier Reef have died, and coral reef-associated biodiversity has declined by sixty three percent. Only an estimated twenty five percent of these species have been formally discovered, leaving a substantial proportion yet to be scientifically classified.  We are no doubt losing species we have yet to identify in the wake of a shifting climate.  
Reduced levels of aragonite, as a result of ocean acidification, continues to be one of the Great Barrier Reef's biggest threats. Healthy reefs support thousands of different corals, fish and marine mammals, but bleached reefs lose their ability to support and sustain life. Coral structural formations create complex habitats critical for providing shelter, breeding grounds, and food sources for numerous marine organisms, including fish, invertebrates, and microorganisms. In turn, corals depend on reef fish and other organisms to clean and regulate algae levels, provide nutrients for coral growth, and keep pests in check. Coral reefs and the species they host have dynamic symbiotic relationships.    
Ocean acidification can also indirectly affect any organism, having reduced growth rates, decreased reproductive capacity, increased susceptibility to disease, and elevated mortality rates.  Bleaching events trigger homogenization of coral composition and losses of structural complexity which can be detrimental to reef fish and other organisms that depend on branching coral for breeding and shelter.  This decrease in ecosystem diversity has direct effects on species diversity.