Short Term Exposure to Heat and Sediment Triggers Changes in Coral Gene Expression and Photo-Physiological Performance

Corals, together with their endosymbiotic Symbiodiniaceae, are known to exhibit a suite of mechanisms for survival under stressful conditions. However, exactly how the host animal responds to varying environmental conditions remains unclear. In this study, we tested two relevant environmental factors that can have deleterious effects on corals: heat and sediment. We examined among-genotype responses of Pocillopora acuta to these factors with RNA-Seq in concert with widely-used tools for assessing the physiological conditions of corals. Heat and sediment treatments were applied in a 2 × 2 crossed experimental design: (1) ∼30°C without sediment (control, “C”), (2) ∼30°C with sediment (sediment-only, “S”), (3) ∼32°C without sediment (heat-only, “H”), (4) ∼32°C with sediment (heat + sediment, “H+S”) over four consecutive days (3-h daily exposure) in ex situ aquarium conditions. A clear differentiation in gene expression patterns was observed in corals exposed to heat alone and to heat with sediment, relative to the control treatment. Few transcripts (∼3) were found to be differentially expressed for corals exposed to sediment only. The greater impact of heat was supported by photo-physiological measurements that showed significant effects on maximum quantum yield and average symbiont density among genotypes of P. acuta. The combined effect of heat and sediment caused a greater reduction in average symbiont density than the effect of sediment alone. Furthermore, “H+S” disrupted the ability of corals to maintain processes involving assembly and disassembly of cilium which suggests a synergistic effect between the two factors. We also found that host-specific genes which were expressed differentially may not be related to their interactions with algal symbionts. Rather, these genes are involved in a variety of biological functions including, but not limited to, cilium biogenesis and degradation, cilia motility, innate and adaptive immune responses, cell adhesion and bone mineralization, and processes involved in the cell cycle. These results reflect the complex response of the host alone. Overall, our findings indicate that acute heat stress in tandem with sediment can depress photo-physiological performance and trigger considerable changes in host gene expression

ACCLIMATIZATION MECHANISMS OF THE CORAL HOLOBIONT TO CHANGING ENVIRONMENTS

Ph.DDOCTOR OF PHILOSOPH

Genome-wide analysis to uncover how Pocillopora acuta survives the challenging intertidal environment

Abstract Characterisation of genomic variation among corals can help uncover variants underlying trait differences and contribute towards genotype prioritisation in coastal restoration projects. For example, there is growing interest in identifying resilient genotypes for transplantation, and to better understand the genetic processes that allow some individuals to survive in specific conditions better than others. The coral species Pocillopora acuta is known to survive in a wide range of habitats, from reefs artificial coastal defences, suggesting its potential use as a starter species for ecological engineering efforts involving coral transplantation onto intertidal seawalls. However, the intertidal section of coastal armour is a challenging environment for corals, with conditions during periods of emersion being particularly stressful. Here, we scanned the entire genome of P. acuta corals to identify the regions harbouring single nucleotide polymorphisms (SNPs) and copy number variations (CNVs) that separate intertidal colonies (n = 18) from those found in subtidal areas (n = 21). Findings revealed 74,391 high quality SNPs distributed across 386 regions of the P. acuta genome. While the majority of the detected SNPs were in non-coding regions, 12% were identified in exons (i.e. coding regions). Functional SNPs that were significantly associated with intertidal colonies were found in overrepresented genomic regions linked to cellular homeostasis, metabolism, and signalling processes, which may represent local environmental adaptation in the intertidal. Interestingly, regions that exhibited CNVs were also associated with metabolic and signalling processes, suggesting P. acuta corals living in the intertidal have a high capacity to perform biological functions critical for survival in extreme environments

Plastic responses in the coral Pocillopora acuta to extreme low light conditions with and without food provision

10.1007/s00227-021-03900-4Marine Biology16811

Emersion?associated responses of an intertidal coral and its suitability for transplantation to ecologically engineer seawalls

10.3390/jmse9101096Journal of Marine Science and Engineering910109

Among-genotype responses of the coral Pocillopora acuta to emersion: implications for the ecological engineering of artificial coastal defences

10.1016/j.marenvres.2021.10531216810531

The Association of Waminoa with Reef Corals in Singapore and Its Impact on Putative Immune- and Stress-Response Genes

Waminoa spp. are acoel flatworms mainly found as ectosymbionts on scleractinian corals. Although Waminoa could potentially represent a threat to their hosts, not enough information is available yet regarding their ecology and effect on the coral. Here, the Waminoa sp.–coral association was analyzed in Singapore reefs to determine the prevalence, host range, and preference, as well as the flatworm abundance on the coral surface. Moreover, the impact of Waminoa sp. on the expression of putative immune- and stress-response genes (C-type lectin, C3, Hsp70 and Actin) was examined in the coral Lobophyllia radians. The association prevalence was high (10.4%), especially in sites with lower sedimentation and turbidity. Waminoa sp. showed a wide host range, being found on 17 coral genera, many of which are new association records. However, only few coral genera, mostly characterized by massive or laminar morphologies appeared to be preferred hosts. Waminoa sp. individuals displayed variable patterns of coral surface coverage and an unequal distribution among different host taxa, possibly related to the different coral growth forms. A down-regulation of the expression of all the analyzed genes was recorded in L. radians portions colonized by Waminoa individuals compared to those without. This indicated that Waminoa sp. could affect components of the immune system and the cellular homeostasis of the coral, also inhibiting its growth. Therefore, Waminoa sp. could represent a potential further threat for coral communities already subjected to multiple stressors

Re-fragmentation of the Coral Echinopora lamellosa (Esper 1795) for Mariculture

Proceedings of The Asian Conference on Sustainability, Energy & the Environment 20199-19Japa

Differential Response of Coral Assemblages to Thermal Stress Underscores the Complexity in Predicting Bleaching Susceptibility.

Coral bleaching events have been predicted to occur more frequently in the coming decades with global warming. The susceptibility of corals to bleaching during thermal stress episodes is dependent on many factors and an understanding of these underlying drivers is crucial for conservation management. In 2013, a mild bleaching episode ensued in response to elevated sea temperature on the sediment-burdened reefs in Singapore. Surveys of seven sites highlighted variable bleaching susceptibility among coral genera-Pachyseris and Podabacia were the most impacted (31% of colonies of both genera bleached). The most susceptible genera such as Acropora and Pocillopora, which were expected to bleach, did not. Susceptibility varied between less than 6% and more than 11% of the corals bleached, at four and three sites respectively. Analysis of four of the most bleached genera revealed that a statistical model that included a combination of the factors (genus, colony size and site) provided a better explanation of the observed bleaching patterns than any single factor alone. This underscored the complexity in predicting the coral susceptibility to future thermal stress events and the importance of monitoring coral bleaching episodes to facilitate more effective management of coral reefs under climate change