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Large aggregations of sylasterid corals have been identified throughout the offshore waters of the Antarctic, Sub-Antarctic and South America. These biodiverse regions are interspersed by deep trenches, channels, sedimentary plains and isolated rocky habitat, which may facilitate or inhibit dispersal over evolutionary and ecological time scales. Deep-sea sampling has increased exponentially, across these benthic habitats, due to collaborative projects such as the Census of Antarctic Marine Life (CAML). Consequently, it is now possible to attempt to combine genetic and taxonomic expertise, explore evolutionary relationships and assess this data in relation to environmental change ‚Äö- both past and future. The biogeographic distribution of stylasterid corals is representative of population isolation, based on the discovery of dissimilar species aggregations throughout sampled regions. To further investigate this biogeographic pattern, I sampled all 33 of the known stylasterid species documented from the Antarctic, Sub-Antarctic, South West Atlantic and Patagonian fiord regions across depths (~10 m - > 2000 m), geographic spatial scales (~10 km ‚Äö- 10, 000 km), and habitat types (shelf, slope, seamount and fiords). Genetic relationships were investigated using DNA sequence data from multiple gene regions including: The mitochondrial ribosomal subunit (16S), cytochrome c oxidase subunit 1 (CO1), and the nuclear Internal Transcribed Spacer (ITS). This data was assigned to four research components to determine 1) the biogeographic distribution of Antarctic and Sub-Antarctic stylasterids (n = 33 species, 14 genera). 2) Phylogenetic relationships based on morphology and genetics (n = 12 species, 8 genera). 3) Phylogenetic relationships incorporating the fossil record, to assess the evolutionary history of stylasterid populations in the Drake Passage (n = 7 species, 6 genera), and lastly, 4) genetic and demographic connectivity between populations to inform conservation management regimes (n = 7 species, 4 genera). Morphological taxonomy combined with mitochondrial DNA sequence data produced a well aligned phylogenetic cladogram. The genetic variability seen in stylasterid 16S and CO1 sequences was comparatively higher than other coral and hydrozoan studies, offering potential for these gene regions in DNA barcoding. This has practical implications including the discovery of new species, cataloguing of Antarctic biodiversity and identification of specimens that are impossible to determine by taxonomic means. However, phylogenetic and taxonomic alignment was only achieved through the incorporation of systematic expertise in species identification, and inter-species relationships remain unresolved when compared to the nuclear ITS gene region. Therefore, the incorporation of more gene regions for study, and the use of molecular taxonomy as a complementary tool, rather than a replacement for traditional systematics is recommended for future studies. When the mitochondrial phylogeny was calibrated with the fossil record, phylogenetic topology represented an evolutionary scenario in which stylasterid ancestors' speciated in the Drake Passage during the Eocene/Oligocene transition boundary from calcite to aragonite sea conditions (~ 34 MYA). The phylogeny also suggests that skeletal bi-mineralogy may have played a central role in the speciation process. The presence of calcite in some genera and literature on the utility of either calcite or aragonite through oceanic time suggest a successional progression toward aragonite mineralogy in response to modern oceanic conditions (Oligocene => modern). Further research in this area may lead to the identification of acclimation states in stylasterid corals, and information on their ability to buffer impending ocean acidification, as the chemical state of the Southern Ocean shifts towards calcite sea conditions in the near future. When investigating genetic population connectivity in the Sub-Antarctic, and across the Polar Front into South America, estimates demonstrate limited to no gene-flow across spatial scales of 300 - > 1000 km. Large scale comparisons were clearly subdivided, and genetic subdivision was evident both among populations either side of, and north of the Polar Front based on CO1 data. However, disparate gene-flow estimates derieved from 16S signify that populations were connected through evolutionary linkages, and connectivity south of the Polar Front may be amplified by the presence of the Antarctic Circumpolar Current (ACC). For fine scale comparision, local estimates of connectivity (~ 200 km) between two Errina spp. fiord populations in Patagonia, Chile, showed no evidence of genetic subdivision (FST = 0, p = 0.6). Similarly, Errina spp in East Antarctica also showed no evidence of genetic subdivision (ITS-1 FST = 0.03 P = 0.165 and ITS-2 FST = 0.002, P = 0.27). However, despite a lack of genetic differentiation in ITS Errina population comparisons, haplotype networks typify a pattern of adaptive radiation from a common ancestor, and upon comparing nucleotide polymorphism in CO1 (˜ìvÑ =0.012 ‚Äö- 0.11), 16S (˜ìvÑ =0 ‚Äö- 0.05), ITS-1 (˜ìvÑ 0 - 0.002) and ITS-2 (˜ìvÑ 0.02 ‚Äö- 0.03) it was determined that relative variability in 16S and ITS represented historic connections, whilst CO1 being more variable, may also be more recent. Taken together, results suggest that a multitude of factors influence stylasterid coral populations, and temporal variation is particularly important in the context of this study. It is recommended that researchers focus on contemporary measures of connectivity, preserve specimens with genetic research in mind (> 90% ethanol preservation at the time of collection), and incorporate more loci to test connectivity across multiple spatial scales and species. The potential use of CO1 or 16S as barcoding genes will help in this process. However, until funding towards more deep-sea Antarctic sampling and molecular information emerges, the data presented in this thesis has ascribed a measure of localised geographic segregation, historic isolation and a limited capacity to recover following benthic disturbance. Substantiating that stylasterid corals congregate in diminutive and isolated populations. Therefore, to preempt anthropogenic damage to coral ecosystems, patterns of geographic isolation need to be incorporated into the design of Antarctic Marine Protected Areas (MPAs) - to preserve essential habitat, buffer climate change, mitigate the effects of ocean acidification, and combat localised impacts such as destructive fisheries which pose a direct threat to coral populations, and their associated taxa.

International audience; Marine biodiversity is a fundamental characteristic of our planet that depends on and influences climate, water quality, and many ocean state variables. It is also at the core of ecosystem services that can make or break economic development in any region. Our purpose is to highlight the need for marine biological observations to inform science and conservation management and to support the blue economy. We provide ten recommenda-tions, applicable now, to measure and forecast biological Essential Ocean Variables (EOVs) as part of economic monitoring efforts. The UN Decade of Ocean Science for Sustainable Development (2021–2030) provides a timely opportunity to implement these recommendations to benefit humanity and enable the USD 3 trillion global ocean economy expected by 2030.

Development of global ocean observing capacity for the biological EOVs is on the cusp of a step-change. Current capacity to automate data collection and processing and to integrate the resulting data streams with complementary data, openly available as FAIR data, is certain to dramatically increase the amount and quality of information and knowledge available to scientists and decision makers into the future. There is little doubt that scientists will continue to expand their understanding of what lives in the ocean, where it lives and how it is changing. However, whether this expanding information stream will inform policy and management or be incorporated into indicators for national reporting is more uncertain. Coordinated data collection including open sharing of data will help produce the consistent evidence-based messages that are valued by managers. The GODS Biology and Ecosystems Panel is working with other global initiatives to assist this coordination by defining and implementing Essential Ocean Variables. The biological EOVs have been defined, are being updated following community feedback, and their implementation is underway. In 2019, the coverage and precision of a global ocean observing system capable of addressing key questions for the next decade will be quantified, and its potential to support the goals of the UN Decade of Ocean Science for Sustainable Development identified. Developing a global ocean observing system for biology and ecosystems requires parallel efforts in improving evidence-based monitoring of progress against international agreements and the open data, reporting and governance structures that would facilitate the uptake of improved information by decision makers.