Showing papers by "Greta S. Aeby published in 2016"

Mutation of the toxR or mshA genes from Vibrio coralliilyticus strain OCN014 reduces infection of the coral Acropora cytherea

Abstract: Thermal stress increases the incidence of coral disease, which is predicted to become more common with climate change, even on pristine reefs such as those surrounding Palmyra Atoll in the Northern Line Islands that experience minimal anthropogenic stress. Here we describe a strain of Vibrio coralliilyticus, OCN014, which was isolated from Acropora cytherea during an outbreak of Acropora white syndrome (AWS), a tissue loss disease that infected 25% of the A. cytherea population at Palmyra Atoll in 2009. OCN014 recreated signs of disease in experimentally infected corals in a temperature-dependent manner. Genes in OCN014 with expression levels positively correlated with temperature were identified using a transposon-mediated genetic screen. Mutant strains harbouring transposon insertions in two such genes, toxR (a toxin regulator) and mshA (the 11th gene of the 16-gene mannose-sensitive hemagglutinin (MSHA) type IV pilus operon), had reduced infectivity of A. cytherea. Deletion of toxR and the MSHA operon in a second strain of V. coralliilyticus, OCN008, that induces acute Montipora white syndrome in a temperature-independent manner had similarly reduced virulence. This work provides a link between temperature-dependent expression of virulence factors in a pathogen and infection of its coral host.

Emerging coral diseases in Kāne'ohe Bay, O'ahu, Hawai'i (USA): two major disease outbreaks of acute Montipora white syndrome.

Abstract: In March 2010 and January 2012, we documented 2 widespread and severe coral disease outbreaks on reefs throughout Kāne'ohe Bay, Hawai'i (USA). The disease, acute Montipora white syndrome (aMWS), manifested as acute and progressive tissue loss on the common reef coral M. capitata. Rapid visual surveys in 2010 revealed 338 aMWS-affected M. capitata colonies with a disease abundance of (mean ± SE) 0.02 ± 0.01 affected colonies per m of reef surveyed. In 2012, disease abundance was significantly higher (1232 aMWS-affected colonies) with 0.06 ± 0.02 affected colonies m(-1). Prior surveys found few acute tissue loss lesions in M. capitata in Ka¯ne'ohe Bay; thus, the high number of infected colonies found during these outbreaks would classify this as an emerging disease. Disease abundance was highest in the semi-enclosed region of south Kāne'ohe Bay, which has a history of nutrient and sediment impacts from terrestrial runoff and stream discharge. In 2010, tagged colonies showed an average tissue loss of 24% after 1 mo, and 92% of the colonies continued to lose tissue in the subsequent month but at a slower rate (chronic tissue loss). The host-specific nature of this disease (affecting only M. capitata) and the apparent spread of lesions between M. capitata colonies in the field suggest a potential transmissible agent. The synchronous appearance of affected colonies on multiple reefs across Kāne'ohe Bay suggests a common underlying factor. Both outbreaks occurred during the colder, rainy winter months, and thus it is likely that some parameter(s) associated with winter environmental conditions are linked to the emergence of disease outbreaks on these reefs.

Gross and Microscopic Lesions in Corals from Micronesia

Abstract: The authors documented gross and microscopic morphology of lesions in corals on 7 islands spanning western, southern, and eastern Micronesia, sampling 76 colonies comprising 30 species of corals among 18 genera, with Acropora, Porites, and Montipora dominating. Tissue loss comprised the majority of gross lesions sampled (41%), followed by discoloration (30%) and growth anomaly (29%). Of 31 cases of tissue loss, most lesions were subacute (48%), followed by acute and chronic (26% each). Of 23 samples with discoloration, most were dark discoloration (40%), with bleaching and other discoloration each constituting 30%. Of 22 growth anomalies, umbonate growth anomalies composed half, with exophytic, nodular, and rugose growth anomalies composing the remainder. On histopathology, for 9 cases of dark discoloration, fungal infections predominated (77%); for 7 bleached corals, depletion of zooxanthellae from the gastrodermis made up a majority of microscopic diagnoses (57%); and for growth anomalies other than umbonate, hyperplasia of the basal body wall was the most common microscopic finding (63%). For the remainder of the gross lesions, no single microscopic finding constituted >50% of the total. Host response varied with the agent present on histology. Fragmentation of tissues was most often associated with algae (60%), whereas necrosis dominated (53%) for fungi. Two newly documented potentially symbiotic tissue-associated metazoans were seen in Porites and Montipora. Findings of multiple potential etiologies for a given gross lesion highlight the importance of incorporating histopathology in coral disease surveys. This study also expands the range of corals infected with cell-associated microbial aggregates.

Assessing threats from coral and crustose coralline algae disease on the reefs of New Caledonia

Abstract: The present study reports the results of the first quantitative survey of lesions on coral and crustose coralline algae (CCA) on reefs in the lagoon of New Caledonia. Surveys on inshore and offshore reefs were conducted at 13 sites in 2010,with12sitesresurveyedin2013.Thirtycoraldiseasesaffecting15coralgenerawerefound,withlowoveralldisease prevalence (,1%). This study extends the known distribution of growth anomalies to the coral genera Platygyra and Hydnophora, endolithic hypermycosis to Platygyra, Leptoria and Goniastrea and extends the geographic range of three CCA diseases. We found the first trematode infection in Porites outside of Hawaii. Disease prevalence differed among coral genera, with Porites having more lesions, and Acropora and Montipora fewer lesions, than expected on the basis of field abundance. Inshore reefs had a lower coral-colony density, species diversity and reduced CCA cover than did the offshore reefs. Disease prevalence was significantly higher on inshore reefs in 2013 than in 2010, but did not change on offshore reefs. The potential ecological impact of individual coral diseases was assessed using an integrative-scoring and relative-ranking scheme based on average frequency of occurrence, prevalence and estimated degree of virulence. The top-five ranked diseases were all tissue-loss diseases. Additional keywords: CCA disease, coral disease, ecological impact of coral disease, endolithic hypermycosis, growth anomalies, trematode infection, white syndrome.