Conservation of deep-sea benthic invertebrates

  • Elin A. Thomas

Student thesis: Doctoral ThesisDoctor of Philosophy


The deep sea is a vast, remote, and relatively unexplored environment that is increasingly viewed as an opportunity for industrial exploitation. Scientists have been calling for the conservation of the deep sea for decades, to preserve the unique benthic habitats and species that thrive in this extreme environment. Conservation efforts continue to be impeded by a severe lack of baseline data such that current records on deep-sea habitats and their associated faunas are inadequate to inform appropriate management and conservation strategies. As anthropogenic threats escalate at an unprecedented rate, the balance between the conflicting forces of conservation need and lack of baseline data increasingly require a precautionary approach. This thesis therefore aimed to combat this conservation impediment, first by addressing the need for improved fundamental knowledge about the systematics, distributions, and relationships of deep-sea benthic invertebrates by contributing new data for understudied taxa, and then by exploring how deep-sea conservation may be achieved with the limited data that are already available. I used phylogenetic analyses, including novel sequence data for holothurians, to better understand species identity and distributions at deep-sea benthic habitats. This understudied group provided a case study to examine how issues of species connectivity, whether locally endemic or globally widespread, are crucial for developing effective conservation measures. Deep-sea holothurians of the genera Elpidia Théel, 1882 and Chiridota Eschscholtz, 1829 were found to have minimal intraspecific genetic variation, despite having widespread geographic distributions, suggestive of sustained connectivity even across environmental barriers. Using deep-sea gastropods, I further established a proof of principle for the application of proteomic analyses as an emerging molecular tool to explore the physiological relationships that underpin the ecology of species at chemosynthetic environments. This provided an important foundation to further our understanding of the complex interactions at insular deep-sea habitats. These analyses suggested that the Antarctic vent gastropod Gigantopelta chessoia C. Chen, Linse, Roterman, Copley & Rogers, 2015 hosts its sulfur-oxidising bacterial endosymbionts exclusively within the specialised trophosome organ, as opposed to the more commonly observed gill-based symbioses, with no evidence of a dual symbiosis. Finally, given the advancing development of the deep-sea mining industry, I demonstrated how a universally known conservation tool, the IUCN Red List of Threatened Species, can be robustly applied to even the most understudied deep-sea taxa in a habitat entirely new to the red-listing process. Using molluscs, I provided the first global assessment of extinction risk for an entire taxonomic group at hydrothermal vents, exemplifying how taxonomy-driven tools can be utilised to support deep-sea conservation and providing a precedent for the application of the Red List across diverse deep-sea species and habitats. This revealed that 62% of all known vent-endemic mollusc species are currently threatened by deep-sea mining and that seabed management and mining regulation have the greatest impact on these extinction risk assessment outcomes. Given the complexities and uncertainties surrounding deep-sea conservation, this thesis summarises how we can utilise and build on existing data to ensure the conservation of deep-sea benthic invertebrates.

Date of AwardDec 2022
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsQueen's University Belfast
SupervisorJulia Sigwart (Supervisor) & Sarah Helyar (Supervisor)


  • Deep sea
  • conservation
  • holothurians
  • molluscs
  • IUCN Red List
  • proteomics
  • phylogenetics

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