Viruses in coral reef ecosystems : implications for nutrient cycling and coral health

Nicole Louise Patten

Viruses are abundant and ubiquitous across aquatic ecosystems; they infect organisms ranging in size from bacteria to whales, and have important roles in biogeochemical processes. However, one ecosystem where information regarding viral ecology is limited is in coral reefs. Consequently, the main objective of this thesis was to increase our understanding of the presence and roles of viruses in coral reef ecosystems. Virus-like particle (VLP) abundances and distributions were quantified in reef waters, carbonate reef sediments and coral reef micro-habitats, using flow cytometry. In addition, transmission electron microscopy (TEM) was used to determine the presence, and to document the morphologies of VLPs within the coral-surface microlayer (CSM), and within scleractinan coral tissues. VLPs were shown to be abundant members of the coral reef planktonic and benthic microbial community, and were directly and indirectly influenced by the release of coral spawn. VLP abundances in sediments, which exceeded reef water VLP abundances by up to two orders of magnitude, were significantly correlated with bacterial abundances, suggesting bacteria were the dominant hosts for VLPs. Between different coral reef micro-habitats, VLP abundances varied by up to 16-fold, with highest VLP abundances co-occurring with highest bacterial abundances within the coral-surface microlayer (CSM) of Acropora muricata. Viral production rates in the CSM of Favia lizardensis exceeded those in overlying waters by 5-fold, further suggesting strong viral pressure occurs within the CSM micro-habitat. VLPs within the CSM of A. muricata and Porites spp. were morphologically diverse and generally distinct from VLPs within overlying reef water. The similarity of many VLPs to known viruses infecting bacteria, archaea, fungi and microalgae, suggest that a range of potential VLPs hosts occur within the CSM. VLPs were also shown to occur within tissues from A. muricata coral colonies. The most common viral morphotype exhibited icosahedral symmetry and was 120 – 150 nm in diameter. However, other VLP morphotypes were also observed, suggesting that different viruses are infecting different organisms within the coral holobiont, or that one host is susceptible to infection from more than one type of virus. The implications for viral infections in coral reef ecosystems are that viral lysis may alleviate nutrient limitation and contribute to the known high productivity rates that occur in these systems. Furthermore, viral associations with corals are likely to have important implications for coral health. The findings of this thesis provide novel information regarding distributions and potential roles that viruses have in coral reef trophodynamics.

Viruses in coral reef ecosystems : implications for nutrient cycling and coral health

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Viruses in coral reef ecosystems : implications for nutrient cycling and coral health

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