Healthy microbes make for a resilient Great Barrier Reef


Maxine Gatt, The Conversation

Healthy microbes make for a healthy coral reef. And if that microbiological community is disrupted by overfishing, pollution or climate change, it can contribute to the decline of reefs.

A three-year study
published this month in Nature Communications, conducted on a reef in the Florida Keys, United States, has shed light on how microbes living on corals are instrumental to keeping coral reefs healthy, and how overfishing, pollution and climate change can destabilise the coral’s natural defence and disrupt ecological communities.

According to the lead author of the study Dr Rebecca Thurber, from Oregon State University, healthy corals normally recover easily from small injuries, such as fish bites.

“In our experiment, 100% of the corals bitten in normal waters recovered. But in the presence of elevated nutrients, 66% died after they were bitten by fish, showing that nutrient pollution increases the vulnerability of corals to normal every day events,” she said.

Although this study focused on Caribbean ecosystems, it can inform threats to the Great Barrier Reef, said Dr Jon Brodie from James Cook University, who was not involved in the study.

Coral bleaching and warming ocean temperatures are already affecting tropical reefs, with coral cover already on the decline.

The addition of overfishing and nutrient pollution interact with the elevated temperatures creating more disease-causing bacteria, and this may make reefs less resilient to disruptive events such as cyclones.

According to Dr Zoe Richards, from Western Australian Museum, who was not involved in the study, the study shows “how easily an innocuous interaction like a fish feeding on a coral can turn deadly in overfished and polluted habitats, especially in summer”.

Adding protection

The results suggest it’s especially important to manage overfishing around important reefs, says Richards. This will help sustain the population of fish that feed on microbes that might otherwise increase in numbers and disrupt the normal microbial ecology.

“This will help suppress algal overgrowth and blooms of harmful bacteria, which are major drivers of coral mortality,” said Richards.

Another strategy to protect reefs is to protect the environment around them.

“Rehabilitating catchment areas, preventing clearing and erosion, along with protecting natural waterways and limiting herbicide and pesticide run-off are integral components of reducing nutrient pollution,” said Richards.

Even though climate change is warming the Great Barrier Reef, reducing the impact of other stressors could help maintain a healthy microbial balance.

“If we reduce ocean pollution and ensure that there are abundant fishes to remove the algae on reefs, corals can likely tolerate some increases in water temperatures,” said Thurber

The Conversation

Maxine Gatt, Editor, The Conversation

This article was originally published on The Conversation. Read the original article.

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Microbes: the tiny sentinels that can help us diagnose sick oceans


Katherine Dafforn, UNSW Australia; Emma Johnston, UNSW Australia; Inke Falkner, and Melanie Sun, UNSW Australia

Microbes – bacteria and other single-celled organisms – may be tiny, but they come in huge numbers and we rely on them for clean water, the air we breathe and the food we eat.

They are nature’s powerhouses but they have often been ignored. We previously lacked the capacity to appreciate truly their diversity, from micro-scales right up to entire oceans.

Recent advancements in genetic sequencing have revealed this diversity, and our research, published in Frontiers in Aquatic Microbiology this week, shows how we can use this information to understand human impacts on an unseen world – making microbes the new sentinels of the sea.

A sea of microbes

The great majority of bacteria and other microbes are extremely beneficial, performing vital roles such as recycling nutrients.

The number of bacteria on Earth is estimated at 5×10³⁰ (or 5 nonillion, if you prefer), and many of them live in the ocean. There are 5 million bacteria in every teaspoon of seawater, and more bacteria in the ocean than stars in the known universe.

Guess how many microbes?
Victor Morozov/Wikimedia Commons, FAL

There are yet more bacteria in the world’s soils and sediments, with estimates of between 100 million and 1 billion bacteria per teaspoon. These sediments are vital for recycling nitrogen, particularly in coastal sediments closest to human populations. Without bacteria and other microbes, sediments would turn into unsightly, pungent piles of waste.

Microbial services are not limited to recycling. Many microbes, including cyanobacteria, function like tiny plants by using sunlight to produce oxygen and sugars. Due to their extraordinary number in the world’s oceans, the amount of oxygen these organisms produce is equal to that of all plants on land.

Marine sentinels

Until recently, finding out just how many different types of microbes there are was relatively difficult. How do you identify and study millions of different organisms that are not visible to the naked eye?

Bacteria, for example, had to be grown in the laboratory in large colonies to be seen. But only 1-3% of bacteria can be cultured successfully.

Advances in genetics together with the development of molecular tools have allowed researchers to investigate marine bacteria in their natural environment. Microbial communities can now be grouped by the role they play in ecosystems and how these groups respond to environmental gradients.

We can use these new tools to measure ecosystem health, which is crucial to managing human impacts on our coastlines, particularly in estuaries. Early studies have found shifts in bacterial community composition to be good indicators of contaminants

Different areas of harbours, such as Sydney Harbour, have distinct bacterial communities. These patterns may be driven by circulation. The outer harbour, which is flushed with seawater on every tidal cycle, is dominated by photosynthetic cyanobacteria. The upper harbour, with less flushing and more runoff, is dominated by soil-related bacteria and those adapted to nutrient-rich environments.

In our waterways, pollutants such as metals bind to fine particles and settle as sediment. This exposes sediment-dwelling organisms to a multitude of toxic products. What effect do these toxic substances have on sediment microbes?

Recent evidence from a large survey of eight estuaries suggests that microbes are far more sensitive to contaminants than larger animals and plants. This survey also revealed that toxic substances were linked to changes in community structure and a reduction in community diversity. This is especially alarming given that a diversity of microbes is essential to nutrient recycling.

Diagnosing wounded seas

It would be great if we could use particular microbes to diagnose human impacts. For instance, certain microbes can indicate water quality.

A technique called metagenomics is revealing the true depth of microbial diversity by pooling DNA sequences from all the species in a sample. It then works backwards to construct a genetic overview of the entire community.

However, while metagenomics can give us important information about the identity of microbes in a community, it can’t tell us what they are doing or how their functions change in response to environmental stressors and human activities.

Metatranscriptomics takes the sequencing approach one step further and characterises gene expression in a microbial community, which can be linked to crucial ecosystem services such as nutrient cycling.

Similar to their use for diagnosis of ailments in humans, molecular tools are being used to diagnose human impacts on earth by observing changes in microbes across polluted and unpolluted environments. They can even detect very small amounts of toxic substances. Because of their diversity, they can potentially be used to detect a wide range of human impacts.

This allows us to identify environmental impacts early, potentially limiting greater loss in larger organisms.

With the new tools to “see” microbes and their importance, we are now perfectly poised to advance our understanding of how microbes are responding to environmental change. They are sentinels of our increasingly human-affected waterways.

The Conversation

Katherine Dafforn, Senior Research Associate in Marine Ecology, UNSW Australia; Emma Johnston, Professor of Marine Ecology and Ecotoxicology, Director Sydney Harbour Research Program, UNSW Australia; Inke Falkner, Community Outreach Coordinator for Sydney Harbour Research Program, Sydney Institute of Marine Science, and Melanie Sun, PhD Candidate – Environmental Research, UNSW Australia

This article was originally published on The Conversation. Read the original article.

Can hungry microbes save the world’s imperiled frogs?


Grist

A Panamanian golden frog, the stoic mascot of mass extinction, is actually still alive in captive breeding programs.ShutterstockA Panamanian golden frog, the stoic mascot of mass extinction, is actually still alive in captive breeding programs.

Humans have shuffled and squelched so many different species that on the death-and-destruction scale, we rank up there with asteroids. One of our latest victims? Amphibians, which have been dying in droves since a mysterious fungal infection went global, wiping out frogs everywhere from the remote jungles of Central America to the insulated glass cases of the Melbourne Zoo.

New research suggests that the pathogen responsible for the frogs’ plague, a fungus nicknamed Bd (that’s Batrachochytrium dendrobatidis to you; “chytrid” to friends) could potentially be staved off by another group of voracious micro-predators. Whether that is enough to bring the Panamanian golden frog and its amphibious ilk back from the brink remains to be seen — but scientists are willing to try, even if that means going microscopic on ecosystem management.

The critically endangered Australian corroboree frog.Australian AlpsThe critically endangered Australian corroboree frog…

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