Disease

Instances of coral disease have been increasing (Richardson, 1988). Disease is a serious threat for corals, with up to 2cm of coral destroyed per day in Florida during a recent outbreak (Richardson et al., 1998). One of the first major instance of coral disease was witnessed in the Caribbean in the 1980s, this dramatically reduced the presence of Acropora (Harvell et al., 1999). There have been many more outbreaks of coral disease since, such as in Puerto Rico in 1996, where 60-90% of each colony was killed (Bruckner and Bruckner, 1997). In 1997 during an outbreak in St. Lucia, disease affected 17 coral species and killed 3.6% of living coral (Nugues, 2002), showing that the effects of disease are highly variable.

Disease outbreaks are more likely to occur after a change in environmental conditions, possibly due to climate change or anthropogenic activities (Harvell et al., 1999). For instance disease outbreaks often occur after bleaching events, such as in the US Virgin Islands where disease caused a 60% decrease in coral cover, after 90% of coral had shown signs of bleaching (Miller et al., 2009). Increases in nutrient concentrations can lead to increases in the severity of the disease (Bruno et al., 2003) and high surface temperatures possibly lead to higher frequencies of certain diseases (Bruno et al., 2007). Anthropogenic activities and climate change also reduce the resilience of the coral meaning that they are more likely to be susceptible to disease (Hughes et al., 2003). With the increases in global temperatures corals are much more likely to bleach and, as disease is often associated with bleaching, disease outbreaks are more likely to occur (Jones et al., 2004).

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