Investigating the Driving Mechanisms Behind Differences in Bleaching and Disease Susceptibility Between Two Scleractinian Corals, Pseudodiploria Strigosa and Diploria Labyrinthiformis

Disease and bleaching are two conditions which commonly lead to coral death. Among coral species, susceptibility to disease and bleaching is variable, and Pseudodiploria strigosa tends to be diseased more than Diploria labyrinthiformis, while D. labyrinthiformis bleaches more readily. The focus of this dissertation was to investigate and compare multiple components of these two coral species, and identify how they may relate to disease and bleaching resistance. Compenetnts examined included the surface mucopolysacharide layer (SML) thickness, gene expression, microbial associates, and a white plague aquarium study. The SML thickness decresased with increasing temperature regardless of coral species, indicating that SML thickness does not likely play a role in differences between susceptablities of these two coral species. However, Diploria labyrinthiformis had a lower mortality rate at 31°C, had fewer differentially expressed genes assossiated with stress, and upregulated genes associated with innate immunity in the summer, all of which may contribute to its relative disease resistance. The bacterial associates of each coral species were also monitored. Differences between the two coral species were primarily caused by Clostridia, Gammaproteobacteria, and rare species which may contribute to the relatively higher disease susceptibility of P. strigosa. Lastly, an aquarium study suggested that a potential pathogen of the Roseobacter clade infects both D. labyrinthiformis and P. strigosa, and might be transmitted by the Cryptochiridae gall crab, indicating that potential disease vectors associated with these two coral species may also play a role in disease resistance and resilience

Season, but not symbiont state, drives microbiome structure in the temperate coral Astrangia poculata.

BACKGROUND: Understanding the associations among corals, their photosynthetic zooxanthella symbionts (Symbiodinium), and coral-associated prokaryotic microbiomes is critical for predicting the fidelity and strength of coral symbioses in the face of growing environmental threats. Most coral-microbiome associations are beneficial, yet the mechanisms that determine the composition of the coral microbiome remain largely unknown. Here, we characterized microbiome diversity in the temperate, facultatively symbiotic coral Astrangia poculata at four seasonal time points near the northernmost limit of the species range. The facultative nature of this system allowed us to test seasonal influence and symbiotic state (Symbiodinium density in the coral) on microbiome community composition. RESULTS: Change in season had a strong effect on A. poculata microbiome composition. The seasonal shift was greatest upon the winter to spring transition, during which time A. poculata microbiome composition became more similar among host individuals. Within each of the four seasons, microbiome composition differed significantly from that of surrounding seawater but was surprisingly uniform between symbiotic and aposymbiotic corals, even in summer, when differences in Symbiodinium density between brown and white colonies are the highest, indicating that the observed seasonal shifts are not likely due to fluctuations in Symbiodinium density. CONCLUSIONS: Our results suggest that symbiotic state may not be a primary driver of coral microbial community organization in A. poculata, which is a surprise given the long-held assumption that excess photosynthate is of importance to coral-associated microbes. Rather, other environmental or host factors, in this case, seasonal changes in host physiology associated with winter quiescence, may drive microbiome diversity. Additional studies of A. poculata and other facultatively symbiotic corals will provide important comparisons to studies of reef-building tropical corals and therefore help to identify basic principles of coral microbiome assembly, as well as functional relationships among holobiont members

Stability of temperate coral Astrangia poculata microbiome is reflected across different sequencing methodologies

The microbiome of the temperate coral Astrangia poculata was first described in 2017 using next-generation Illumina sequencing to examine the coral’s bacterial and archaeal associates across seasons and among hosts of differing symbiotic status. To assess the impact of methodology on the detectable diversity of the coral’s microbiome, we obtained near full-length Sanger sequences from clone libraries constructed from a subset of the same A. poculata samples. Eight samples were analyzed: two sets of paired symbiotic (brown) and aposymbiotic (white) colonies collected in the fall (September) and two sets collected in the spring (April). Analysis of the Sanger sequences revealed that the microbiome of A. poculata exhibited a high level of richness; 806 OTUs were identified among 1390 bacterial sequences. While the Illumina study revealed that A. poculata’s microbial communities did not significantly vary according to symbiotic state, but did vary by season, Sanger sequencing did not expose seasonal or symbiotic differences in the microbiomes. Proteobacteria dominated the microbiome, forming the majority (55% to 80%) of classifiable bacteria in every sample, and the five bacterial classes with the highest mean relative portion (5% to 35%) were the same as those determined by prior Illumina sequencing. Sanger sequencing also captured the same core taxa previously identified by next-generation sequencing. Alignment of all sequences and construction of a phylogenetic tree revealed that both sequencing methods provided similar portrayals of the phylogenetic diversity within A. poculata’s bacterial associates. Consistent with previous findings, the results demonstrated that the Astrangia microbiome is stable notwithstanding the choice of sequencing method and the far fewer sequences generated by clone libraries (46 to 326 sequences per sample) compared to next-generation sequencing (3634 to 48481 sequences per sample). Moreover, the near-full length 16S rRNA sequences produced by this study are presented as a resource for the community studying this model system since they provide necessary information for designing primers and probes to further our understanding of this coral’s microbiome

Removal of detritivore sea cucumbers from reefs increases coral disease

Abstract Coral reefs are in global decline with coral diseases playing a significant role. This is especially true for Acroporid corals that represent ~25% of all Pacific coral species and generate much of the topographic complexity supporting reef biodiversity. Coral diseases are commonly sediment-associated and could be exacerbated by overharvest of sea cucumber detritivores that clean reef sediments and may suppress microbial pathogens as they feed. Here we show, via field manipulations in both French Polynesia and Palmyra Atoll, that historically overharvested sea cucumbers strongly suppress disease among corals in contact with benthic sediments. Sea cucumber removal increased tissue mortality of Acropora pulchra by ~370% and colony mortality by ~1500%. Additionally, farmerfish that kill Acropora pulchra bases to culture their algal gardens further suppress disease by separating corals from contact with the disease-causing sediment—functioning as mutualists rather than parasites despite killing coral bases. Historic overharvesting of sea cucumbers increases coral disease and threatens the persistence of tropical reefs. Enhancing sea cucumbers may enhance reef resilience by suppressing disease

Stability of temperate coral astrangia poculata microbiome is reflected across different sequencing methodologies

The microbiome of the temperate coral Astrangia poculata was first described in 2017 using next-generation Illumina sequencing to examine the coral’s bacterial and archaeal associates across seasons and among hosts of differing symbiotic status. To assess the impact of methodology on the detectable diversity of the coral’s microbiome, we obtained near full-length Sanger sequences from clone libraries constructed from a subset of the same A. poculata samples. Eight samples were analyzed: two sets of paired symbiotic (brown) and aposymbiotic (white) colonies collected in the fall (September) and two sets collected in the spring (April). Analysis of the Sanger sequences revealed that the microbiome of A. poculata exhibited a high level of richness; 806 OTUs were identified among 1390 bacterial sequences. While the Illumina study revealed that A. poculata’s microbial communities did not significantly vary according to symbiotic state, but did vary by season, Sanger sequencing did not expose seasonal or symbiotic differences in the microbiomes. Proteobacteria dominated the microbiome, forming the majority (55% to 80%) of classifiable bacteria in every sample, and the five bacterial classes with the highest mean relative portion (5% to 35%) were the same as those determined by prior Illumina sequencing. Sanger sequencing also captured the same core taxa previously identified by next-generation sequencing. Alignment of all sequences and construction of a phylogenetic tree revealed that both sequencing methods provided similar portrayals of the phylogenetic diversity within A. poculata’s bacterial associates. Consistent with previous findings, the results demonstrated that the Astrangia microbiome is stable notwithstanding the choice of sequencing method and the far fewer sequences generated by clone libraries (46 to 326 sequences per sample) compared to next-generation sequencing (3634 to 48481 sequences per sample). Moreover, the near-full length 16S rRNA sequences produced by this study are presented as a resource for the community studying this model system since they provide necessary information for designing primers and probes to further our understanding of this coral’s microbiome

The microbiome of African penguins (Spheniscus demersus) under managed care resembles that of wild marine mammals and birds

Abstract Animals under managed care in zoos and aquariums are ideal surrogate study subjects for endangered species that are difficult to obtain in the wild. We compared the fecal and oral microbiomes of healthy, managed African penguins (Spheniscus demersus) to those of other domestic and wild vertebrate hosts to determine how host identity, diet, and environment shape the penguin microbiome. The African penguin oral microbiome was more similar to that of piscivorous marine mammals, suggesting that diet and a marine environment together play a strong role in shaping the oral microbiome. Conversely, the penguin cloaca/fecal microbiome was more similar to that of other birds, suggesting that host phylogeny plays a significant role in shaping the gut microbiome. Although the penguins were born under managed care, they had a gut microbiome more similar to that of wild bird species compared to domesticated (factory-farmed) birds, suggesting that the managed care environment and diet resemble those experienced by wild birds. Finally, the microbiome composition at external body sites was broadly similar to that of the habitat, suggesting sharing of microbes between animals and their environment. Future studies should link these results to microbial functional capacity and host health, which will help inform conservation efforts

Season, but not symbiont state, drives microbiome structure in the temperate coral Astrangia poculata

Abstract Background Understanding the associations among corals, their photosynthetic zooxanthella symbionts (Symbiodinium), and coral-associated prokaryotic microbiomes is critical for predicting the fidelity and strength of coral symbioses in the face of growing environmental threats. Most coral-microbiome associations are beneficial, yet the mechanisms that determine the composition of the coral microbiome remain largely unknown. Here, we characterized microbiome diversity in the temperate, facultatively symbiotic coral Astrangia poculata at four seasonal time points near the northernmost limit of the species range. The facultative nature of this system allowed us to test seasonal influence and symbiotic state (Symbiodinium density in the coral) on microbiome community composition. Results Change in season had a strong effect on A. poculata microbiome composition. The seasonal shift was greatest upon the winter to spring transition, during which time A. poculata microbiome composition became more similar among host individuals. Within each of the four seasons, microbiome composition differed significantly from that of surrounding seawater but was surprisingly uniform between symbiotic and aposymbiotic corals, even in summer, when differences in Symbiodinium density between brown and white colonies are the highest, indicating that the observed seasonal shifts are not likely due to fluctuations in Symbiodinium density. Conclusions Our results suggest that symbiotic state may not be a primary driver of coral microbial community organization in A. poculata, which is a surprise given the long-held assumption that excess photosynthate is of importance to coral-associated microbes. Rather, other environmental or host factors, in this case, seasonal changes in host physiology associated with winter quiescence, may drive microbiome diversity. Additional studies of A. poculata and other facultatively symbiotic corals will provide important comparisons to studies of reef-building tropical corals and therefore help to identify basic principles of coral microbiome assembly, as well as functional relationships among holobiont members