Coral diseases can be triggered by abiotic (i.e temperature, sedimentation, and pollution) and biotic factors (ie bacteria, fungi, viruses).  Coral diseases and coral bleaching are commonly studied since researchers are realizing that increased temperatures due to climate change and increased anthropogenic activity may be increasing the presence of outbreaks. Coral bleaching is thought to be caused by increasing warm temperatures which stops the symbioses relationship between zooxanthellae and coral since the algal photosynthesis is disrupted. Sometimes some of the bleaching has been found to be caused by disease and not stress from temperature (Jones, et al and McWilliams, et al.). Finding the affects diseases and bleaching have on coral community structure now can help us understand how warmer Ocean temperatures may affect outbreaks and how even continued development may harm coral reefs. Some of these diseases are difficult to identify so more research is needed to document them. Picture: a brain coral found in Bermuda to have had BBD

It is widely thought that anthropogenic impacts that release pollution and sewage can cause an increase in prevalence of coral disease. Past work has shown that coral disease associates with pollution and that its affects increase as human development increase. Global climate change is causing temperature increase and will continue rising, while sea levels also rise, extreme weather becomes more frequent and more intense, ocean acidification increases, and ocean circulation changes (Bates). Some of the extreme weather that may be caused by climate warming is an increase in hurricane seasons. Hurricanes have been found to have a significant affect on coral health in that it on average reduces coral reefs by about 17% (Gardner, et al.). Garnder found that hurricanes may explain much of the coral reef decline in the 1980s but other stressors in addition to hurricanes have affected reefs in the 1990s.

These changes may be affecting the coral reef health in Bermuda as past studies have shown biodiversity is decreasing as a result of climate change. A monitoring program at the Bermuda Institute of Oceanic Sciences has begun to evaluate multiple long-term changes in temperature, water quality, acidification, dissolved inorganic carbon concentrations, and ecological surveys (Jones). The ecological surveys look at the changes that the coral is exhibiting including mortality. This is a long term project since climate change has a large scale effect on biodiversity so larger temporal scales are needed.

The Black Band Disease was reported in Bermuda in the 1970s but has spread to other locations over the years.  Black band disease affects Scleractinians caused by pathogenic microbial consortium which involves sulfate reducing bacteria (Desulfovibrio  spp.), sulfate oxidizing bacteria (Beggiatoa spp.), and cyanobacteria (Phormidium corallyticum). The black band is a mat that moves a few millimeters per day leaving a bare coral skeleton. The vertical position of the band depends on the photic response of cyanobacterial filaments which is a light intensity-dependent. The color of the band depends on the thickness of the band. This leaves dead coral since the band causes an anoxic, sulfide-rich microenvironment. The rate that the band moves can be between 2 mm/day to 1 cm/day.  

Bermuda has a significant disadvantage compared to other coral reef areas in that it is isolated from other corals so any impact the Bermuda reef is long term. Cold winters also slow down recover from this type of damage so its impacts may be severe (Moore).  The coral does not have high genetic variability so they are less likely to be able to respond to climate change fast enough. So this reef may be more susceptible to damage from BBD triggered by warming and/or anthropogenic activity.

The goal for this project is to conduct a survey on four different locations in Bermuda and see if these areas contain black band disease. The four locations that are studied are North Rock(1), Whalebone Bay(2), John Smith’s Bay(4), and a beach by the Causeway(3) (see map on left). At these sites, a survey of brain corals was conducted. Presence of Black Band Disease (BBD) infection was recorded and if it was active. Water temperature and wave action were collected to record the present conditions of each area. The long-term monitoring data would have been used to see. if there are differences between these sites but this is not available from BIOS at this current time. (Map: BIOS)