Coral reefs are among the most diverse natural system on Earth and corals are the most important piece of this great mosaic. As we know, they are animals able to create a complex structure which provide food and protection to thousands of other organisms such as fish, mollusks, seastars, and so on. Despite being so simple (actually not so simple as we believe), corals are animals like us, although we are much more complex than corals, we do share many similarities in terms of requiring oxygen for to breathing, food for energy our systems can fail and we get sick.
It is not an uncommon sight when we come across corals that seem to be in distress due to particular diseases or bacteria. A disease can be classified as any deficiency of vital body functions, systems or organs and is a natural aspect of coral populations and also one mechanism in which coral populations are kept place. Coral diseases can be caused by bacteria, viruses or fungi and may cause significant changes in the community structure, species diversity, reproduction and growth rates as well as the abundance of reef-associated organisms. There are several mechanisms and environmental conditions that support disease transmissions such as high coral cover, water quality and certain predators (corallivorous fish, polycheates and gastropods).
Similar to human populations, certain coral colonies with high abundances are also more susceptible to diseases and this is because some diseases spread more rapidly within crowded populations for example the white band disease, a highly contagious disease that affect any healthy coral tissue through direct contact. The band, which ranges between few millimeters to 10 centimeters can work its way from the base of the coral colony to the branching tips at a rate of approximately 5 millimeters per day. The result is a dead bare skeleton which may later be colonized by filamentous algae. Diseases such as white band disease, white pox, aspergillosis and white plague are believed to be caused by known bacterial pathogens whereas some diseases such as black band disease may be caused by a complex association of microbes and may contain up to 50 different bacterial types within the disease.
Another disease which has also been identified on one of the coral frames is skeleton-eroding band disease (SEB) which is a visible as a black or dark grey band that slowly advances over corals, leaving a spotted region in its wake. SEB was first noticed 1988 near Papua New Guinea and then in Great Barrier Reef and also Mauritius in 1990. It was only in 1994 when surveys around the Red Sea regarded this condition as a unique disease and is now considered of the commonest disease of corals in the Indian and Pacific Oceans, especially in warmer more polluted waters. SEB is a progressive disease and they can spread over an infected coral at around 2 millimeters per day in colonies of Acropora.
Many coral diseases have not been thoroughly characterized and the causative agents for many diseases still remain unclear. Understanding the causes and impacts of coral diseases allow managers and conservationists to understand how coral reef management and human impacts affect the spread and severity of these diseases and make informed management decisions. Here at Thudufushi we do our best to inform all visiting guest about the importance of corals and how to behave when in the water during excursions. Our coral conservation project also aim at restoring damaged coral fragments by attaching them onto steel structures which would, given the right conditions, grow into a small coral reef. As unfortunate as it is to see corals fighting against these diseases, there is not much we can do for them in nature. As for the coral frames, we do our best to remove any infected corals before they spread to the healthy corals
Further reading and video:
https://www.aims.gov.au/docs/research/biodiversity-ecology/threats/coral-disease.html
https://www.youtube.com/watch?time_continue=31&v=PxeMPB6DlsYhttps://www.researchgate.net/publication/235409567_Coral_diseases_in_aquaria_and_in_nature
