Coral Health and Disease in the Pacific: Vision for Action

Where are these pathogens coming from?External sources of pathogens that have been proposed include terrestrial runoff(Aspergillus), sewage (Serratia marcescens), and African dust events (Aspergillus).Pathogens may also already be present in the marine environment. Reservoirs of P.corallyticum (along with other cyanobacteria) occurred as biofilms on the surface ofsediment patches present in depressions on healthy M. annularis, M. cavernosa and C.natans colonies (Richardson, 1996). These may be dispersed via movement of watermasses, especially during storms (Bruckner and Bruckner, 1997), and transmitted throughvarious vectors like damselfish, parrotfish, fireworms and coral-eating snails (Williamsand Miller, 2005; Aeby and Santavy, 2006).Bacteria also occur on corals in a non-infectious state. Coral mucus is a richprotein-carbohydrate complex that harbors a diverse community of bacteria and othermicrobiota, and these communities are known to be distinct from the surrounding water(Rohwer and Kelley, 2004). Bacterial diversity varies between healthy corals, healthyparts of diseased corals, and diseased tissue (Rohwer et al., 2002; Pantos et al., 2003).Environmental changes can affect the physiological equilibrium between bacteriaassociated with the corals and their hosts, or stimulate the growth of other bacteria(Pantos et al., 2003). The coral-microbe relationship can be disrupted by nutrient andorganic carbon loading by overstimulating the growth of these microbes, which mayresult in coral mortality (Kuntz et al., 2005). Under stressful conditions one or more ofthese microbes may become virulent or affect the resistance of the host, and subsequentlytrigger onset of an infectious disease.Are disease outbreaks associated with changing environmental conditions?Diseases may be infectious (produced by parasites and pathogens) or noninfectious(genetic mutations, produced by environmental factors). The frequency andseverity of infectious diseases may affected by changing environmental conditions(elevated SST, declining water quality), human induced alterations of the marineenvironment (e.g., input of land-based pollutants; dredging, coastal development), andhurricanes and other natural disturbances. Increased temperatures may causephysiological stress and/or trigger the development of pathogenic agents that otherwisewould remain non virulent.Increased abundance and virulence of at least five diseases (BBD, WPX, DSD,ASP and YBD) has been associated with elevated seawater temperatures, with declines inthese conditions reported during winter months (Kuta and Richardson, 2002, Alker et al.,2001; Patterson et al., 2002, Gil-Agudelo and Garzón-Ferreira, 1999 and Weil, 2004).Disease outbreaks may also be more severe during or immediately following bleachingevents due to a lower resistance of host corals. Widespread and severe outbreaks of WP-II were observed in Puerto Rico, USVI and the eastern Caribbean following the 2005Caribbean bleaching events (J. Miller, coral list posting; Weil, 2006). Other naturalfactors, such as habitat characteristics, composition, cover and abundance of susceptiblecorals, the amount of macroalgae, and presence/absence of certain key indicator speciessuch as Diadema may also influence the occurrence and severity of coral diseases.Patterns of disease distribution obtained from the Global Coral Disease Database haveshown that 97% of the areas affected by disease in the Caribbean prior to 2000 correlate147