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Oligotrophic (sub-)tropical oceans receive intense incident ultraviolet radiation (UV, 280–400 nm) and their water columns are highly transparent due to their nutrient-deficient state. This combination suggests a high potential for adverse effects on organisms, yet only few reports describe the UV exposures received in these waters and the associated impacts on marine biota. Here, we aimed to investigate the UV bio-optics of various open ocean locations and, using the Red Sea as a representative oligotrophic environment, we investigated the pattern of UV attenuation over a wide latitudinal range, quantified UV exposures in the water column, and determined impacts of UVB (280–320 nm) on indigenous phytoplankton and scleractinian corals. Globally, the lowest average downwelling diffuse attenuation coefficients (Kd) in the UV spectrum were recorded in the ultra-oligotrophic Indian Ocean Subtropical Gyre (Kd(313nm): 0.110 m-1) and South Pacific Gyre (Kd(313nm): 0.098 m-1), while aCDOM(λ) was ~1–2 orders of magnitude higher than ap(λ), In the Red Sea, UV attenuation mirrored the prevailing latitudinal gradient in nutrients, with the lowest and highest Kd(313) of 0.130 m-1 and 0.357 m-1 measured in the far north and in the south of the basin, respectively. Central Red Sea waters were most transparent to UV in late summer, i.e., a few weeks after incident irradiances and SSTs reach their annual maximum. Although, the projected increase of SST due to climate change means that extreme UV exposure and temperatures could coincide in the near future. This finding is of particular relevance since we found that Red Sea diatom species such as C. closterium are highly sensitive to UVB-induced photoinhibition and cell decay (LRD50: 11.4 kJ). Water temperature also governed the UVB sensitivity of Synechococcus sp., although this group exhibited a high resistance overall (LRD50: 57 kJ to non-detectable). For corals, we found that UVB-removal generally had little impact on the oxidative stress levels and photophysiology of S. pistillata and P. verrucosa from shallow waters, but considerably accelerated the acclimation of upward transplanted corals, which highlights that UVB is a crucial stressor that governs the photoacclimation capacity of Red Sea corals.

Coral reefs are the most diverse marine ecosystems of significant ecological and economic importance, globally. Increasing environmental stress imposed by global warming, ocean acidification and pollution has led to the continuous decline of coral reefs. For reefs to thrive and survive, they rely on the stable endosymbiosis between coral animal and photosynthetic algae. The fragile symbiotic relationship is dependent on a balanced metabolic exchange, which is easily disturbed by stress, consequently leading to the loss of the endosymbiotic algae - a process known as bleaching. Since corals energetically rely on the algae, the breakdown of symbiosis can have fatal consequences. However, the underlying molecular and cellular mechanisms of this symbiosis are thus far poorly understood. The small sea anemone Aiptasia has provided an experimentally tractable model organism, furthering our understanding on the function of symbiosis and hence, coral susceptibility and resilience to stress. Nonetheless, this model organism is comparatively young and therefore, requires innovative approaches as well as establishment and optimization of protocols. In this thesis, we applied transcriptomic, proteomic and epigenomic tools in Aiptasia, with the aim to assess the dynamics of symbiosis and thermotolerance. Heat stress studies, on Aiptasia's originating from geographically distinct regions, provided insight into the cnidarian-algae symbiosis mechanisms and the role of metabolic compatibility in symbiosis. Furthermore, findings elucidated that associating with thermotolerant algae can improve the cnidarian host's tolerance, potentially acting as a form of local adaptation. Finally, the role of epigenetic mechanisms in cnidarian symbiosis was investigated, by optimizing Chromatin Immunoprecipitation (ChIP) and establishing the genomic landscape of histone 3 lysine 9 acetylation (H3K9ac) in Aiptasia. These new results will enable progressing Aiptasia further as a model organism and thus, advance our understanding on the complex mechanisms of coral symbiosis.

Corals are critical to marine biodiversity and human welfare. Coral reefs cover <1% of the seafloor but support ~1/3 of all marine species. Approximately 1.5 billion people live within 100 km of coral reefs, relying upon them for food, income from tourism, and protection from storms. Their economic value has been estimated at $375 billion annually. The foundation of coral reefs is the intracellular symbiosis between corals and photosynthetic dinoflagellates of the family Symbiodiniaceae. Tropical corals satisfy up to 95% of their nutritional requirements through photosynthesis, and their ability to construct reefs is biochemically coupled to photosynthesis. While permitting corals to thrive, photosymbiosis also increases their exposure to environmental stressors and vulnerability to climate change. Reliance on photosynthesis restricts reef-building corals to shallow, clear, tropical waters, where they experience higher temperatures and UV exposure. The generation of reactive oxygen species by the symbiont also exposes corals to greater oxidative stress. The symbiosis is particularly sensitive to climate change: all of the mass coral bleaching events have occurred since 1982, driven by elevated ocean temperatures. Molecular cross-talk between host and symbiont impacts resilience of the coral holobiont and resistance to bleaching. Unfortunately, we know little about how photosymbiosis impacts expression or activity of coral genes. Tropical corals engage in an obligate symbiosis with Symbiodiniaceae, so we cannot study their gene expression in a stable aposymbiotic state. However, the northern star coral, Astrangia poculata, engages in a facultative symbiosis with Symbiodiniaceae. I used RNA sequencing to investigate how symbiosis impacts gene expression in A. poculata, focusing on genes implicated in photosymbiosis: antioxidant enzymes (specifically superoxide dismutases) and the NF-κB signaling pathway. From an improved transcriptome assembly, I recovered core elements of a primitively simple NF-κB signaling pathway and a rich complement of SOD proteins. 273 coral transcripts—many associated with protein metabolism and vesicle-mediated transport— were differentially expressed in symbiotic versus aposymbiotic corals. Unlike in the facultatively symbiotic sea anemone Exaiptasia, symbiosis was not associated with depressed NF-κB transcript levels. IKKε, a potential positive regulator of NF-κB activity, was strongly up-regulated, as was one particular superoxide dismutase.

Plastic pollution has become of public concern recently and only in the last decades the need of quantifying loads of plastic in the marine environment and identifying their ultimate destination has been urged as a mean to point at where interventions should concentrate. The Arabian seas (Red Sea and Arabian Gulf) have oceanographic features that candidate them as accumulation zones for marine plastics, but, especially the Red Sea, are largely unexplored. The dissertation here presented provides significant advances in the understanding of the marine plastic distribution in the two basins. Despite the initial hypothesis, the Red Sea was found to hold a remarkably low abundance of plastic particles in its surface waters. Similarly, previous assessments have reported the same in the Arabian Gulf. In line with the global estimates, only a small portion of the plastic that is discarded yearly in the marine environment is found in its surface waters, implying the presence of removal processes. However, the unexpectedly low loads of floating plastics in the Arabian seas indicate that sinks are likely more significant here than elsewhere. In the Red Sea, an extensive survey of macroplastic stranded on shores, globally considered a major sink of marine plastic, has indicated that Avicennia marina mangrove forests, through the mesh created by their pneumatophores, contribute significantly more than unvegetated shores in retaining plastics. Loads of plastic in the Arabian Gulf mangrove stands, more impacted by coastal development than stands in the Red Sea, are even larger. The role of mangroves as significant sinks of plastics is further corroborated by the finding that the burial rates of plastic in their sediments follow an exponential increase in line with the global plastic production increase, ultimately demonstrating that plastic is likely sequestered there permanently. Mangrove forests alone are, however, not enough to justify the mismatch between plastic inputs and loads in surface waters. The experimental finding showed here that coral structures can passively trap substantial loads of microplastics and the large extension of reefs, especially in the Red Sea, suggest that reefs might constitute a missing sink of marine plastic in the basin worth exploring.

Understanding the past sensitivity of ice sheets and sea level rise in a warmer climate is essential to future coastal planning under the threat of climate change, as accurately modeling impending scenarios depends primarily on data from the past. Extreme warm events during the Quaternary and Neogene periods hold much of the information needed to predict future global climate conditions due to anthropogenic and natural forcings, and may provide unique glimpses of how much future sea level rise can be expected on both short- and long-term timescales. Constraining global mean sea level (GMSL) during past warm periods becomes increasingly difficult the further back in time one goes, especially as precise dating of globally distributed paleoshorelines, along with long-term vertical displacement rates, is essential for establishing GMSL and ice volume history. However, placing chronological constraints on shorelines beyond the limit of U-series radiometric dating (~600 kyr), or at high latitude sites lacking coral, has remained elusive. Even relatively recent warm periods, such as the Last Interglacial (~117-129 ka) has proved challenging for reconstructing GMSL, primarily due to uncertainties in long-term vertical deformation rates and timing of when the highstand occurred. The first two chapters of this thesis address the dating of carbonate shorelines older than ~500 kyr through refinement of the strontium isotope stratigraphy dating methodology. I apply these techniques to a well-known location with numerous uplifted fossil shorelines (Cape Range, Western Australia) to provide the first geochemically derived ages on three fossil shorelines spanning the Pleistocene to the Miocene. Accurate dating and mapping at this location allows correction of long-term vertical displacement. In the last chapter, I use these rates of uplift, in conjunction with twenty new 230Th/U-ages on corals from Western Australia, to refine the timing and peak elevation of the Last Interglacial sea level highstand. Chapter 1 re-evaluates strontium isotope stratigraphy dating techniques for chronologically constraining fossil shorelines from ~0.5 to >30 Ma. Using marine terraces from South Africa, Western Australia, and the Eastern United States as examples, this chapter presents a refined sampling and dating methodology to overcome limitations on diagenetically altered samples, which are ubiquitous in older carbonate shorelines. Discussion on best practices for constraining maximum or minimum ages includes a novel scoring methodology for alteration and a sequential leaching procedure that is specifically suited for shallow-water biogenic carbonate fauna. In Chapter 2, I apply the revised strontium isotope stratigraphy dating methodology to three previously unknown aged terraces in Cape Range, Western Australia. The results obtained show Late-Miocene, Late-Pliocene and Mid-Pleistocene shorelines, which I then use to reconstruct the vertical uplift history of the anticlinal structure and relative rates of deformation. This study is the first to directly date the three terraces, and provides the deformation history necessary for constraining Last Interglacial sea level at Cape Range. In addition, we are able to place maximum relative sea level constraints on all three of these older shorelines. Chapter 3 builds upon the previous chapter by focusing on the Last Interglacial sea level history along ~300 km of coastline in Western Australia (Cape Range and Quobba). This chapter presents new U-series ages on multiple coral heads that are among the highest in-situ corals ever dated in Western Australia, with ages spanning from ~125.3 – 122.6 ka. Detailed geomorphic analysis, particularly at Cape Range, constrains the relative sea level highstand to 6.9 ± 0.4 m. When glacial isostatic adjustment models are applied to the age and elevation data, the resulting Eemian GMSL highstand occurred between 125.5-123.0 ka and reached an elevation between 4.9 and 6.7 m. This is later in the Interglacial and lower in elevation than many recent studies suggest. This dissertation focuses on refining sea level highstands from the Last Interglacial to the Late Miocene in a relatively small (but historically important) region of Western Australia. However, the methodologies presented here provide a powerful multi-proxy dating and mapping approach, which, when applied to regions with multiple marine terraces, can greatly improve the reliability of younger shoreline elevations by reducing neotectonic and dynamic topography uncertainties. The carbonate screening techniques and 87Sr/86Sr stratigraphy dating described here are applicable to a wide range of marine carbonates, with the ability to place accurate chronologic constraints on shorelines from 0.5 to >30 Ma. As I show in chapter 3, when combined with 230Th/U-dating on Late Pleistocene coral in places where multiple marine terraces exist, valuable long-term vertical deformation constraints can allow for far more accurate analysis of sea level in younger paleo shorelines (i.e. Last Interglacial).

In the present study the species boundaries of the scleractinian coral genus Goniopora from the Saudi Arabian Red Sea were investigated. An integrated morpho-molecular approach was used to better clarify the complex scenario derived from traditional classification efforts based on skeletal morphology. Traditional taxonomy of this genus considers skeletal morphology first and polyp morphology as a secondary discriminating character. This leads to potential complication due to plasticity in skeletal features within a species. To address this issue, molecular analyses of evolutionary relationships between nine traditional morphospecies of Goniopora from the Red Sea were performed and were used to re-evaluate the informativeness of macromorphological and micromorphological features. Between four and six putative molecular lineages were identified within Goniopora samples from the Saudi Arabian Red Sea on the basis of four molecular markers: the mitochondrial intergenic spacer between Cytochrome b and the NADH dehydrogenase subunit 2, the entire nuclear ribosomal internal transcribed spacer region, the ATP synthase subunit β gene, and a portion of the Calmodulin gene. The results were strongly corroborated by three distinct analyses of species delimitation. Subsequent analyses of micromorphological and microstructural skeletal features identified the presence of distinctive characters in each of the molecular clades. Unique in vivo morphologies were associated with the genetic-delimited lineages, further supporting the molecular findings. The proposed re-organization of Goniopora will resolve several taxonomic problems in this genus while reconciling molecular and morphological evidence. Reliable species-level identification of Goniopora spp. can be achieved with polyp morphology under the proposed revision.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18102号 / 理博第3980号 / 新制||理||1574(附属図書館) / 30960 / 京都大学大学院理学研究科生物科学専攻 / (主査)講師 宮崎 勝己, 教授 朝倉 彰, 教授 疋田 努 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Coral reefs are "constructional physiographic features of tropical seas consisting fundamentally of a rigid calcareous framework made up mainly of the interlocked and encrusting skeletons of reef-building (hermatypic) corals (Wells,1957). The principal organisms responsible for the construction of modern day coral reefs, the stony corals, comprise the cnidarian order Scleractinia, which is closely allied to the sea anemones (Actinaria). Individual polyps secrete a calcium carbonate skeletal cup (calyx) beneath the basal epidermis. In most coral species the polyps remain connected by living tissue forming a colony and calcium carbonate is deposited beneath the basal epidermis of the entire colony, thereby constructing a three-dimensional mass of calcium carbonate which increases in size with the passage of time. The living tissues of reef building corals are packed with unicellular symbiotic dinoflagellates termed zooxanthellae which have been shown to be of Importance in both the calcification of the skeleton and in production of organic material on the reef.

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