Sponge-microbe associations survive high nutrients and temperatures.

Area of Science:

• Marine Biology
• Ecology
• Microbiology

Background:

• Coral reefs face threats from rising sea temperatures and ocean acidification.
• Marine sponges are vital to reef ecosystems, filtering large water volumes and hosting unique microbial communities.
• Sponges' microbial symbionts are crucial for host health and survival.

Purpose of the Study:

• To investigate the impact of elevated nutrients and seawater temperature on the health and microbial communities of the Great Barrier Reef sponge Rhopaloeides odorabile.
• To assess the stability of bacterial, archaeal, and eukaryotic microbial associations under simulated environmental stress.

Main Methods:

• Manipulative experiments exposing R. odorabile to elevated nutrient levels (10 µmol/L total nitrogen) and temperatures (31°C).
• Analysis of microbial community dynamics using 16S rRNA gene pyrotag sequencing for bacteria.
• Assessment of archaeal communities via 16S rRNA gene library sequencing and amoA gene analysis using denaturing gradient gel electrophoresis (DGGE).
• DGGE was also used to analyze eukaryotic community composition.

Main Results:

• R. odorabile showed no visual changes after 7 days of exposure to elevated nutrients and temperature compared to control groups.
• Bacterial communities remained highly conserved at phylum and operational taxonomic unit (OTU) levels (97% similarity), with 19 phyla and 1743 OTUs identified.
• Archaeal associations (Thaumarchaeota) and eukaryotic communities were also stable across all experimental treatments, indicating robust microbial symbiosis.

Conclusions:

• The microbial symbionts of R. odorabile demonstrate significant resilience to short-term increases in nutrient concentrations and sub-lethal temperatures.
• These findings highlight the stability of sponge holobionts and their potential to withstand current environmental changes impacting coral reefs.