Impacts of polyaromatic hydrocarbons (PAHs) on oligotrophic tropical marine organisms and food-chains

  • Ananya Ashok

Student thesis: Doctoral Thesis


Polyaromatic hydrocarbons (PAHs) are oil derived toxic and persistent pollutants prevalent across the oceans from pelagic waters to coral reefs. The Great Barrier Reef (GBR) in Australia and the Red Sea are important oligotrophic marine ecosystems susceptible to oil contamination. This Ph.D. dissertation aims to advance our understanding on PAH tolerance, accumulation dynamics and trophic transfer in oligotrophic ecosystems where those aspects remain poorly explored. In this dissertation, a new, highly-sensitive method combining stable carbon isotope labelling and cavity ring-down spectroscopy (CRDS) was developed to quantify PAH accumulation and applied in a series of ex situ food chain experiments with two representative PAHs, 13C-phenanthrene and 13C-pyrene. The experiments conducted with Acropora millepora – a common reef-building coral in the GBR, showed faster accumulation of both PAHs by dissolved uptake, although dietary exposure caused more consistent accumulation. Phenanthrene was not toxic to the coral photosystem II in either exposure mode but biomagnification increased with increasing food-chain complexity. In contrary, pyrene led to loss of symbionts accompanied by reduction in photosynthetic efficiency and coral bleaching, especially via dietary uptake. Also, microbial communities and food webs are relevant components of oligotrophic waters. We identified contrasting sensitivities among key autotrophic and heterotrophic microbial populations in the chronically oil exposed Red Sea to a mixture of 16 PAHs recognized as priority pollutants. The differential tolerance pointed towards localized selection for resistant strains in some populations. Some PAH toxicity thresholds approached ambient PAHs concentrations suggesting that any increase in pollution loads will hold consequences for these important microbial groups and their ecological functions.
Date of AwardApr 2022
Original languageEnglish (US)
Awarding Institution
  • Biological, Environmental Sciences and Engineering
SupervisorSusana Agusti (Supervisor)


  • PAH
  • coral
  • food chain
  • bioaccumulation
  • biomagnification
  • oil pollution
  • marine pollution
  • great barrier reef
  • red sea

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