Invading microbes: Another threat for our vanishing coral reefs

New evidence suggests that coral reefs are facing another danger that puts their existence at risk – inland sources could be introducing invasive bacteria and fungi, disrupting these delicately maintained ecosystems.

Using ‘Illumina-based next generation sequencing’, the research team were able to analyse the samples collected around the southeast coast of Florida, including inlet discharges, sewage plant outfalls and coral tissue, to compare their prokaryotic and fungal communities. They also used software called SourceTracker to determine where microbes found in the coral reef samples had originated from.

The research was published on March 24th, 2017 in Applied and Environmental Microbiology.

Coral reefs are a vital ecosystem – around 25% of all marine life rely on them for food, reproduction and for a place to call home. Coral isn’t just important for fish – these organisms provide us with food, protect land from storms and tsunamis, and could even play a role in medicine – with applications to treat heart disease, bacterial infections and even cancer.

However, if current trends continue, these beautiful ecosystems could be lost to us forever. We’ve lost around half of the world’s coral reefs, and things such as overfishing and careless fishing activities, pollution and climate change are ensuring that the rest will follow unless we do something to stop it.

Coral reefs need a delicately balanced microbiome to survive – but the foreign microbes from inland sources could be killing them. Image credit –










In this research, the team found evidence to suggest that sources such as wastewater treatment plant outfalls and coastal inlet discharges could be transferring microbes from their original land-based locations to the coral reefs, upsetting the balance of the microbial communities which are already established.

Reefs are an example of what’s known as a ‘holobiont’ – the coral polyp coexists in a symbiotic relationship with various microorganisms including bacterial, fungal and viral species. These communities are maintained as precise levels, ensuring the health of the coral. The introduction of foreign microbes by these inland sources can upset this microbial balance, leading to various diseases that can be a death sentence for the coral.

Michael Sadowsky, a member of the research team and a professor of microbiology at the University of Minnesota’s Biotechnology Institute, said in a press release, “The metagenomics data we have now strongly suggests that anthropogenic input sources are becoming established on reefs.”

While there are two major categories of danger facing the planet’s coral reefs, global (such as climate change) and local (for example pollution), it is the local threats which are more immediately manageable.

With threats to the coral reef’s microbial community only gaining attention in recent years, this study provides crucial new information on sources of pollution which could be damaging these ecosystems, and could potentially be used to identify ways in which to limit this threat.

But more work needs to be done to prove that damage to the coral is being done by these land-based microbes. “We would need to infect part of a pristine reef in a lab mesocosm study and follow the microbial ecology – the growth and survival – of the microorganisms that become established on the reef,” professor Sadowsky stated.

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