Advisor: Professor Susana Agusti
Polyaromatic hydrocarbons (PAHs) are oil-derived toxic, bioaccumulative 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 tropical marine environments characterized by the presence of complex microbial food-chains and vulnerable coral reefs. Due to human activity, both these regions are susceptible to oil, and therefore PAH contamination. This Ph.D. dissertation aims to advance our understanding on PAH tolerance, accumulation dynamics and trophic transfer in these two 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 stable carbon isotope labelled 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 uptake provided more consistent accumulation. Phenanthrene was not toxic to the coral photosystem II in either exposure mode although biomagnification increased with increasing food-chain complexity. In contrary, the four ring PAH, pyrene, led to loss of symbionts accompanied by reduction in photosynthetic efficiency and coral bleaching, especially via dietary uptake. Also, microbial communities 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.
Ananya Ashok is a Ph.D. candidate under the supervision of Professor Susana Agusti in the Biological Oceanography Lab at the Red Sea Research Center, KAUST. Previously, she completed her Masters in Fisheries Sciences with a specialization in Aquatic Environmental Management from the Central Institute of Fisheries Education in Mumbai, India. She has been the recipient of a Junior Research Fellowship (2013 – 15) from the Indian Council of Agricultural Research as well as recognitions such as the Best Fisheries Graduate of India (2014) and International Climate Champion with the British Council in India (2011 – 13). In her doctoral research, she answers key questions on the impacts of oil-derived pollution in the marine environment.