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Sea anemones of the Southern Ocean : ecology, phylogenetic relationships, life history, and population genomics
thesisposted on 2023-05-27, 10:42 authored by Leslie WatsonLeslie Watson
The overall aim of this study was to understand the distribution, abundance and diversity of sea anemones from the Southern Ocean. Diversity and abundance of sea anemones in the Southern ocean is poorly studied with little information since their first discovery in the early 1900s. Understanding the species and the roles they play in the Southern Ocean can help assess their impact on other species and the impacts of environmental stress and disturbances on the Southern Ocean system. Sea anemone distribution and their relationship to their environment was surveyed with the use of a Remote Operated Vehicle (ROV) and photoquadrats from three Antarctic regions, Dumont d'Urville, Casey, and Davis Station. Through the use of an ROV at Dumont d'Urville Station, hundreds of metres of the benthic environment were covered in a short time frame allowing connections to be made between sea anemones and their environment at depths greater than can be reached diving. A positive association between sea anemones distribution and ecological engineers was found. Bryozoans and ascidians are ecological engineers that create vast ranges of habitat in this region allowing for increased biodiversity through substrate attachment for sea anemones and other benthic organisms. At Casey and Davis Station, photoquadrat surveys were used to establish fine-scale sea anemone habitat preferences and community relationships along with understanding the impacts of human disturbance on sea anemone distribution. Through the use of fine-scale photoquadrat studies, sea anemone characteristics (burrowing versus non-burrowing species) were linked to distribution and habitat preferences. Two distinct sea anemone types were found in this study; large sea anemones that require substrate attachment and smaller burrowing sea anemones that prefer muddy sediment. The large sea anemones that require substrate attachment were generally found in rocky regions, with the exception of some sedimentary habitats where ecological engineers, ascidians, were used as attachments. The large sea anemones were associated with habitats that contained higher diversity of species, which was related to the availability of substrate attachment and the protection the rocky habitats provide. The burrowing sea anemones were positively associated with other burrowing species and species that did not require substrate attachment. At Casey Station, there was greater sea anemone abundance at human impacted sites, but the cause for this greater abundance is unknown. The use of both ROV and photoquadrat surveys are important tools in understanding environmental connections to species distribution and abundance. Another important step in understanding connections between a species and its environment is being able to correctly identify species. Biodiversity in the Southern Ocean is poorly understood with many of the species being identified taxonomically in the early 1900s, leaving many species to be incorrectly identified or grouped together as one species. Sea anemones in the Southern Ocean are an important predator and prey species in the ecosystem, and our current knowledge on Antarctic anthozoan biodiversity is less than 50%. A more modern approach using genetic techniques could help resolve some of these discrepancies, such as DNA sequencing. The mitochondrial regions CO1 and 16S along with the nuclear region ITS and ITS2 were used to test their potential as barcoding regions for Antarctic sea anemones. A total of 381 individual sea anemones were collected from the Continental shelf region and Macquarie Island tidal pools, and 9 different species were distinguished from these samples using the consensus sequences from combined CO1 and 16S regions. A total of 12 species were distinguished using the ITS2 region. The full ITS region was only obtained for the Macquarie Island species and a total of 5 species were distinguished. However, these regions could not resolve discrepancies at genus or higher levels. This study showed that with the use of DNA sequencing, sea anemones from the Southern Ocean can be identified using these methods and they have potential to resolve some of the taxonomic discrepancies at a species level, increasing our knowledge of Southern Ocean sea anemone biodiversity. Sea anemone reproductive strategies were also examined to understand a species life history and verify reproductive modes of a species. A small seasonal collection of Isotealia antarctica over the austral summer in West Antarctica found that this species was gonochoric with individuals having well developed sperm or oocyte throughout the summer. This suggests that reproductive cycle of I. antarctica is not dependent on the increased food supply generally associated with polar summers. The oocytes are relatively large, also suggesting the potential for lecitotrophism. Two of the samples obtained from the end of the austral summer were identified as Urticinopsis antarctica. These two samples were also gonochoric and gametic tissues were also well developed with oocytes being similarly large suggesting that U. antarctica may have a similar reproductive strategy as I. antarctica. More histological work throughout the year from more individuals and from multiple populations can help narrow down the reproductive cycles and mode of these species. Molecular techniques are also beneficial in understanding the phylogeography of a species. Many species in the Southern Ocean have circumpolar distributions. Genotype by Sequencing is a new Next Generation Sequencing tool that can be utilized to help determine if there is gene flow amongst species' circumpolar populations or detect cryptic speciation. Urticinopsis antarctica is a species that has a circumpolar distribution and four different populations of U. antarctica were examined for circumpolar relationships (three East Antarctic locations, one West Antarctic location). The three East Antarctic locations were panmictic with gene flow occurring amongst the regions, whereas the West Antarctic was genetically differentiated from the other three regions. This suggests that there is isolation by distance, which may eventually lead to speciation. Also, fine-scale population structure was examined within the Casey Station region. Small genetic differentiation was found between sites that were impacted by anthropogenic stressors, such as sewage outfalls, waste dumps, and heavy traffic areas (Wharf), versus non-impacted sites. This suggests the potential for anthropogenic activity does have an effect on U. antarctica. However, the impacted sites are also found within the same embayment and there is potential that local geographical and hydrological barriers may also be causing an isolation of this population from other populations, which may lead to potential speciation. This study is first to examine distribution, abundance, diversity, and population genomics of sea anemones from the Southern Ocean at a large and fine-scale levels. I used multiple techniques to begin to build bridges between different aspects of Southern Ocean sea anemone ecology. Obtaining a baseline for the different species of sea anemones and their abundance and distribution helps us to understand future changes in the Southern Ocean benthic ecosystem, which is already seeing the effects from environmental stress, disturbances and climate change.
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