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Faculty of Graduate Studies

Eva MacLennan

  • BSc Hons. (University of Victoria, 2017)
Notice of the Final Oral Examination for the Degree of Master of Science

Topic

Community composition, biodiversity, and elemental content in novel urban intertidal communities

Department of Biology

Date & location

  • Friday, October 24, 2025
  • 9:00 A.M.
  • Clearihue Building, Room B007

Examining Committee

Supervisory Committee

  • Dr. Rana El-Sabaawi, Department of Biology, University of Victoria (Supervisor)
  • Dr. Amanda Bates, Department of Biology, UVic (Member)
  • Dr. Hugh MacIntosh, Collections Manager, Invertebrate Zoology, Royal BC Museum (Outside Member)

External Examiner

  • Dr. Sarah Dudas, Department of Biology, UVic

Chair of Oral Examination

  • Dr. Maycira Costa, Department of Geography, UVic

Abstract

As populations increase and cities grow, so will the impacts of marine urbanization and the proliferation of artificial structures along urban coastlines. The majority of research on marine artificial structures has focussed on seawalls or breakwaters and is concentrated in a few harbours; dock and pier pilings, prolific structures on urbanized coastlines, are underrepresented. We examined differences in community composition, biodiversity, functional diversity, and phosphorus content between artificial piling habitats and natural rocky reefs in an urban estuary in Victoria, British Columbia. Community composition and diversity differed significantly between natural reefs and artificial piling structures, and differences were driven dominantly by the most abundant taxa. Many taxa were unique to one substrate type, but exclusion of rare taxa did not affect differences between habitat types. There were more algae species and more abundant grazers in natural reef habitats, and more non-indigenous species in piling habitats. Natural sites had higher community phosphorus than artificial sites. There was considerable variation in phosphorus content among intertidal organisms. Mollusc soft tissues were enriched in phosphorus, but when their shells were included, algae were more phosphorus-rich. The patterns in biodiversity and non-indigenous species abundance seen here align with findings from other studies on seawalls and breakwaters, suggesting that eco-engineering interventions for seawalls may be applicable to pilings as well. We were also able to extend these observations to the northeast Pacific Ocean, a region that remains underrepresented in the literature. More uniquely, incorporating elemental analysis offers a novel stoichiometric perspective and highlights potential effects of urban structures on nutrient cycling. These approaches lay the foundation for future research identifying the drivers of these patterns and developing engineering solutions to address them.

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