Giulia Marchioro - AIMS@JCU

Giulia Marchioro

mail-marchioro93@gmail.com

Masters by research
CCMAR, University of Algarve, Faro, Portugal

Giulia Marchioro

mail-marchioro93@gmail.com

Masters by research
CCMAR, University of Algarve, Faro, Portugal
Coupling compositional shifts in coral microbiome to environmental fluctuations and changes in coral host physiology

Giulia Marchioro, a MSc student at the University of Algarve in Portugal, will be at AIMS doing an internship as part of her MSc thesis focusing on the diagnostic potential of coral microbiomes to indicate coral health.

Coupling compositional shifts in coral microbiome to environmental fluctuations and changes in coral host physiology

2018 to 2019

Project Description

Over the last decade, studies focusing on the coral microbiome have revealed the importance of microbial communities to the homeostasis and health of their hosts. In this context, microbial genetic diversity has been investigated across a variety of environmental gradients and the occurrence of both stable and transient microbial lineages has become apparent. Because microbial communities constantly adjust to their environment and available resources, shifts in community composition have been proposed to provide an early indication of coral reef health. Coral microbiomes also vary significantly between distinct animal compartment, with coral tissue and coral surface mucus exhibiting distinct microbial communities. Whereas the tissue-associated community has been hypothesised to more directly respond to variation in the physiology of the coral animal and its associated photosymbionts (the zooxanthellae), the community inhabiting the surface mucus is in more direct contact with the surrounding seawater and is therefore suggested to change in response to environmental fluctuations. However, no direct evidence for these hypotheses has so far been reported.

Here, we aim at investigating, in parallel:

1) seasonal changes in host physiology for two distinct coral species inhabiting the Great Barrier Reef (Acropora tenuis and Acropora millepora);

2) seasonal changes in the composition of both tissue- and mucus- associated microbial communities for both A. tenuis and A. millepora;


3) seasonal changes in biophysical properties of the surrounding seawater environment.
Combining these three datasets will allow answering the question: Do microbial communities associated with different coral holobiont compartments respond differently to seasonal fluctuations in host physiology and in the external environment? Results will also provide insights into the use of particular microbial lineages as indicators of coral host health and/or environmental variation in coral reefs.

Project Importance

Validated microbial indicators can subsequently be incorporated into monitoring programs, reef report cards and health indices. Microbial indicators will make a significant contribution to an Integrated Reef Monitoring Program and improve our capacity to rapidly predict ecosystem declines due to cumulative pressures, thereby guiding early management interventions aimed at conserving the unique biodiversity of the Great Barrier Reef.

Project Methods

All methods described below will be applied to samples already collected from two inshore Great Barrier Reef sites (Magnetic Island and Orpheus Island, Queensland, Australia), on a monthly basis, for a total period of 16 months (January 2015 – May 2017). Samples comprise 3 colony replicates of each coral species for each sampling time point, for a total of n=90.


1) Host and photosymbiont physiology
A number of spectrophotometric assays will be applied to measure changes in cellular and metabolic activity within the coral host tissue or zooxanthellae over the sampling period. These will be performed on coral tissue homogenate samples kept in the -80C freezer since collection.
Chlorophyll concentration will be analysed after acetone extractions, total protein content will be quantified using a colorimetric protein assay, carbohydrate content will be quantified using a phenol-sulfuric acid method, and chromoprotein contents will also be determined. Detection of activity of the enzymes catalase (scavenger of reactive oxygen species) and phenoloxydase (catalyser of melanin synthesis pathway triggered by pathogens and thermal stress) will provide insight on stress response and coral immunity. All measured parameters will be standardized to protein contents.

2) Shifts in microbial communities
Ongoing advances in sequencing platforms and data analysis pipelines now offer the possibility of analysing microbiomes at a higher genetic resolution. This allows for the relationships between corals and their associated microbiomes to be explored at finer taxonomic levels, and we hypothesise this will lead to the recognition of new paradigms on how stable or transient coral microbiomes really are over space and time. Here we will resolve amplicon sequence variants (ASVs) using 16S rRNA gene data originating from samples kept in the -80C freezer. For this purpose, the analysis pipeline qiime2 (https://qiime2.org/) will be used on an already existing sequencing dataset. The taxonomic affiliation of the groups involved in compositional changes over time will be determined.

3) Environmental variation
At each time point, water was subsampled in duplicate for dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), particulate organic carbon (POC), dissolved inorganic nutrients (DIN), total suspended solids (TSS), Chlorophyll a concentration and salinity. Samples were further analysed according to the standard procedures of the Australian Institute of Marine Science (AIMS, Townsville, Australia)13. Sediment characteristics such as grain size distribution and total organic carbon (TOC) and nitrogen (TON) content were assessed for each sampling event. Seawater temperatures will be obtained from AIMS long-term monitoring temperature records (http://eatlas.org.au/).

Data analysis will employ a multitude of multivariate statistical tests commonly used in the study of ecological communities.

Project Results

Results will provide insights into the use of particular microbial lineages as indicators of coral host health and/or environmental variation in coral reefs.

Keywords

Bacteria,
Biostatistics,
Climate change,
Coral reefs,
Corals,
Disease,
Management tools,
Microbial,
Microbiology,
Natural disturbance,
Physiology,
Pollution,
Quantitative marine science,
Temporal change

Supervised By:

David Bourne (JCU)

Nicole Webster (AIMS)

Pedro Rodrigues Frade (AIMS)