Algae as Reservoirs for Coral Pathogens

Abstract

Benthic algae are associated with coral death in the form of stress and disease. It's been proposed that they release exudates, which facilitate invasion of potentially pathogenic microbes at the coral-algal interface, resulting in coral disease. However, the original source of these pathogens remains unknown. This study examined the ability of benthic algae to act as reservoirs of coral pathogens by characterizing surface associated microbes associated with major Caribbean and Indo-Pacific algal species/types and by comparing them to potential pathogens of two dominant coral diseases: White Syndrome (WS) in the Indo-Pacific and Yellow Band Disease (YBD) in the Caribbean. Coral and algal sampling was conducted simultaneously at the same sites to avoid spatial effects. Potential pathogens were defined as those absent or rare in healthy corals, increasing in abundance in healthy tissues adjacent to a disease lesion, and dominant in disease lesions. Potentially pathogenic bacteria were detected in both WS and YBD and were also present within the majority of algal species/types (54 and 100% for WS and YBD respectively). Pathogenic ciliates were associated only with WS and not YBD lesions and these were also present in 36% of the Indo-Pacific algal species. Although potential pathogens were associated with many algal species, their presence was inconsistent among replicate algal samples and detection rates were relatively low, suggestive of low density and occurrence. At the community level, coral-associated microbes irrespective of the health of their host differed from algal-associated microbes, supporting that algae and corals have distinctive microbial communities associated with their tissue. We conclude that benthic algae are common reservoirs for a variety of different potential coral pathogens. However, algal-associated microbes alone are unlikely to cause coral death. Initial damage or stress to the coral via other competitive mechanisms is most likely a prerequisite to potential transmission of these pathogens.

Farming behaviour of reef fishes increases the prevalence of coral disease associated microbes and black band disease

“…Intensive territorial grazers cultivate turf algae and detritus as food resources [16], which appear to harbour potential pathogens linked to BBD and may act as a coral disease pathogen reservoir. Turf algae have previously been shown to harbour pathogens that are associated with coral disease [30,36]. However, fish behaviour has not previously been directly linked to reservoirs of potential pathogens that may cause coral disease or the actual increased prevalence of coral disease.…”

Responses of Coral-Associated Bacterial Communities to Local and Global Stressors

“…These authors also proposed that fleshy algae can alter reefs by increasing both bacterial respiration and pathogenic invasion (Barott et al, 2012). Moreover, algae may act as reservoirs for coral pathogens (Sweet et al, 2013) and thus enhance disease events. Algae harbor distinctly different microbial communities than corals (Barott et al, 2011;Vega Thurber et al, 2012) and produce more carbon exudate that can stimulate heterotrophic microbial growth in reef waters (Haas et al, 2011).…”

Evidence for rapid, tide-related shifts in the microbiome of the coral Coelastrea aspera

“…All collections were made in an area *20 m 9 20 m at a similar tidal height. Interactions with other organisms and sediment have been shown to cause the onset of coral disease (Nugues et al 2004;Carlos et al 2013;Sweet et al 2013), and sediments have even been proposed as a potential 'seed bank' for certain microbial associates of corals (Carlos et al 2013). With this in mind, we carefully selected colonies to avoid potential contamination from these sources.…”