Metagenomic sequencing reveals altered bacterial abundance during coral-sponge interaction: Insights into the invasive process of coral-killing sponge Terpios hoshinota.

The coral-killing invasive sponge, Terpios hoshinota, causes extensive mortality to live corals and is a potential threat to reefs at different geographical locations. However, to date, the invasive mechanism remains largely unknown. In this study, we aimed to understand the bacterial competition between sponge and coral hosted bacteria when sponge outcompetes corals. We analysed the bacterial community of Terpios-invaded coral tissue, and the adjacent healthy tissue of sponge-invaded Favites colonies from Palk bay reef (South East Asia) of the Indian Ocean by using next-generation sequencing. Comparative analysis revealed similar bacterial diversity in both healthy and sponge covered coral tissues. However, relative abundance found to be differed between the groups. Terpios covered coral tissue had higher bacterial abundance than the healthy coral tissue. Bacterial phyla such as Bacteroidetes, Proteobacteria, Firmicutes, Actinobacteria, and Verrucomicrobia live both in sponge covered and healthy coral tissue. Notably, many of the lower abundant bacteria in healthy coral tissue (abundance <1%) became the most abundant in sponge-invaded tissue. In particular, the genus Neisseria, Bacteroides, and members of Pseudoalteromonas predominant in sponge-invaded tissue. Similar bacterial diversity between normal and and sponge-invaded coral tissues suggest that bacteria follow an exploitative competition, which might favoured sponge growth over corals.

Differential bleaching and recovery pattern of southeast Indian coral reef to 2016 global mass bleaching event: Occurrence of stress-tolerant symbiont Durusdinium (Clade D) in corals of Palk Bay.

Information about coral community response to bleaching on Indian reefs is much more limited compared with Indo-Pacific reefs, with no understanding of algal symbionts. We investigated a reef in Palk Bay to understand the coral community response to 2016 bleaching event and to reveal dominant symbiont type association in four common coral genera. Out of 508 colonies surveyed, we found 20.9% (106) mortality in 53.8% (n = 290) of bleached corals. We found differential bleaching and recovery pattern among coral genera. Bleaching was most prevalent in Acropora (86.36%), followed by Porites (65.45%), while moderate to no bleaching was recorded in Favites 5.88%, Symphyllia 51.11% and Favia 55.77%, Platygyra 41.67%, Goniastrea 41.83%. Pre-bleaching and post bleaching samplings revealed changes in dominant symbiont type following bleaching only in Acropora (Cladocopium, Clade C to Durusdinium Clade D) while no such changes were found in other coral genera hosted Clade D. This is the first observation of coral symbiont diversity in the Indian reef.

Emergence of a multi host biofilm forming opportunistic pathogen Staphylococcus sciuri D26 in coral Favites abdita.

Corals are hotspots of ocean microbial diversity and imbalance in the composition of coral associated microbes has been mostly correlated with the emergence of climate change driven diseases which affect the overall stability of the reef ecosystem. Coral sampling was performed by SCUBA diving at Palk Bay (latitude 9.271580, longitude 79.132203) south Indian coast. Among the 54 bacterial isolates, an isolate MGL-D26 showed comparatively high biofilm formation and was identified as Staphylococcus sciuri based on phylogenetic analysis. The production of exopolysaccharide (EPS) confirmed the formation of a slimy EPS matrix associated with the biofilm. The biofilm formation in S. sciuri D26 was induced significantly by UV exposure followed by other stress factors including pollution, agitation, and salinity. The strain inhibited innate immune factors of corals such as melanin synthesis and phenoloxidase. Challenge experiments in a model organism Aiptasia sp. showed pathogenicity of S. sciuri. Histopathological analysis revealed tissue invasion by S. sciuri which was a predisposing factor leading to mortality in challenged Aiptasia sp. However, specific disease condition of corals infected by S. sciuri requires continuous field monitoring and further investigation. Based on the findings, S. sciuri was a first reported multi-host opportunistic pathogen which has emerged in corals under environmental stress.

Outbreaks of Acropora white syndrome and Terpios sponge overgrowth combined with coral mortality in Palk Bay, southeast coast of India.

Acropora white syndrome (AWS) and Terpios sponge overgrowth (TSO) are serious threats to coral communities in various regions; however, information on these 2 lesions in the Indian Ocean is much more limited than in the Indo-Pacific. The present study revealed the impact of these lesions on the Palk Bay reef, India, and covered an area of 7 km2. In total, 1930 colonies were permanently monitored to assess incidences of AWS and TSO and consequent mortality for a period of 1 yr. TSO affected 5 coral genera and caused 20.7% mortality; overall prevalence increased from 1.3% (n = 25) to 25.5% (n = 492). In contrast, AWS only affected Acropora colonies and caused a mortality of 8%; overall prevalence increased from 0.9% (n = 17) to 12.9% (n = 249). Year-round monitoring revealed an increasing trend of both AWS and TSO, followed by temperature rise. These results add to the known geographic distribution of these coral diseases and reveal the impacts of AWS and TSO on coral reefs in the Indian Ocean.

Variation in black and white band disease progression in corals of the Gulf of Mannar and Palk Bay, Southeastern India.

Information on the progression of coral diseases and transmission to live corals is scarce despite the fact that coral disease poses one of the most lethal threats to the survival of coral reefs. In this study, in situ progression rates of lesions similar to black band disease (BBD) and white band disease (WBD) were measured in different species of corals from the Gulf of Mannar (GoM) and Palk Bay, southeastern India, during the period between January and December of 2009. Maximum progression rates of 3 and 1.6 cm mo-1 for BBD and WBD, respectively, were observed during May, when the temperature exceeded 30°C. The annual progression rate was 10.9 and 4.9 cm yr-1 for BBD at GoM and Palk Bay, respectively. Significant variation in the progression rate (p < 0.001) was observed between months in all the examined species. Significant correlation between temperature and disease progression rates for BBD (R2 = 0.875, p ≤ 0.001) and WBD (R2 = 0.776, p ≤ 0.001) was recorded. Rates of disease progression were higher in Palk Bay than in GoM. This could be attributed to the higher temperature coupled with higher anthropogenic activities in Palk Bay. Severe mortality was observed due to both BBD and WBD. No sign of recovery was noticed in the disease-affected colonies at either study site. Anthropogenic activities should be checked, and further research on both the transmission and progression rate and role of the diseases in reef dynamics should be carried out to understand the causal factors in reef degradation and generate a plan to manage the reef properly.

Coral diseases are major contributors to coral mortality in Shingle Island, Gulf of Mannar, southeastern India.

The present study reports coral mortality, driven primarily by coral diseases, around Shingle Island, Gulf of Mannar (GOM), Indian Ocean. In total, 2910 colonies were permanently monitored to assess the incidence of coral diseases and consequent mortality for 2 yr. Four types of lesions consistent with white band disease (WBD), black disease (BD), white plaque disease (WPD), and pink spot disease (PSD) were recorded from 4 coral genera: Montipora, Pocillopora, Acropora, and Porites. Porites were affected by 2 disease types, while the other 3 genera were affected by only 1 disease type. Overall disease prevalence increased from 8% (n = 233 colonies) to 41.9% (n = 1219) over the 2 yr study period. BD caused an unprecedented 100% mortality in Pocillopora, followed by 20.4 and 13.1% mortality from WBD in Montipora and Acropora, respectively. Mean disease progression rates of 0.8 ± 1.0 and 0.6 ± 0.5 cm mo-1 over live coral colonies were observed for BD and WBD. Significant correlations between temperature and disease progression were observed for BD (r = 0.86, R2 = 0.75, p < 0.001) and WBD (R2 = 0.76, p < 0.001). This study revealed the increasing trend of disease prevalence and progression of disease over live coral in a relatively limited study area; further study should investigate the status of the entire coral reef in the GOM and the role of diseases in reef dynamics.